Tokamak Experimental Power Reactor: Basic Considerations and Initiation of Studies at Oak Ridge

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THERMONUCLEAR DIVISION

TOKAMAK. EXPERIMENTAL POWER REACTOR: BASIC CONSIDERATIONS ANL INITIATION OF STUDIES AT OAK RIDGE

P. N. Haubenreich, editor

This report was prepared as an account of work sponsored by the United Stales Government. Neither the United States nor the United States Energy Research and Development Administration, nor any of APRIL 1975 their employees, nor any of their contractors, subcontractors, or their employees, nukes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use ivould not infringe privately owned rights.

NOTICE This document contains Information of a preliminary nature and was prepared primarily for internal use at the Oak Rids* National Laboratory. It is subiect to revision or correction and therefore doss not represent a final report.

OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee 37830 operated by UNION CARBIDE CORPORATION for the U.S. Energy Research & Development Administration iii

CONTENTS

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ABSTRACT ACKNOWLEDGEMENTS , viii 1. INTRODUCTION 1 1.1 Background 1 1.2 Organization of Report- 2 2. SCOPE, OBJECTIVES, AND ORGANIZATION OF STUDIES 3 2.1 Scope 4 2.2 Objectives in FY-1975 and -1976 4 2.3 Definition of Task Areas 5 2.3.1 EPR Project Definition* 5 2.3.2 Plasma Engineering and Physics ® 2.3.3 Blanket and Energy Conversion • • 6 2.3.4 Shielding 7 2.3.5 Tokamak Device Engineering 7 2.3.6 Tritium 7 2.3.7 Tokamak Support Systems 8 2.3.8 Materials and Fabrication 8 2.3.9 Integration of Design 8 2.3.10 Assembly and Maintenance 9 2.3.11 Facility Planning and Engineering 9 2.3.12 Program Management 9 2.4 Allocation of Effort in FY-1975 10 2.5 Task Statements 10 2.5.1 EPR Project Definition 10 2.5.2 Plasma Engineering and Physics 13 2.5.3 Blanket and Energy Conversion IS 2.5.4 Shielding 16 2.5.5 Tokamak Device Engineering 17 2.5.6 Tritium 18 BLANK PAGE XV

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2.5.7 Tokamak Support Systems 19 2.5.8 Materials and Fabrication 19 2.5.9 Integration of Design 20 2.5.10 Assembly and Maintenance 20 2.5.11 Facility Planning and Engineering 21 2.5.12 Program Management ...... 22 3. INITIAL OBSERVATIONS AND RESULTS 23 3.1 Definition of the EPR Project 23 3.1.1 Fusion Reactor Features to be Included in EPR . 23 3.1.2 EPR Operating Power Level 27 3.1.3 Goals of Long-Term Operation 32 3.1.4 Required Input from Research and Development Programs 33 3.2 Plasma Physics and Engineering 36 3.2.1 Guidelines for an EPR 36 3.2.2 Sources of Design Information 37 3.2.3 Time-In dependent Model 38 3.2.4 Time-Dependent Model 40 3-3 Blanket and Energy Conversion 44 3.3.1 Conceptual Design Criteria 44 3.3.2 Candidate Materials 45 3.3.3 Outstanding Problems 46 3.3.4 Progress 47 3.4 Neutronics and Photonics Calculations 49 3.4.1 Criteria for Calculations 49 3.4.2 Methods of Calculation 49 3.4.3 Progress to Date 50 3.5 Magnet Considerations . . . * 51 3.6 Tritium 55 3.6.1 Process Requirements for Primary Tritium System * 56 3.6.2 Radiological Aspects of Tritium Handling Systems 59 V

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3.7 Materials and Fabrication 61 3.7.1 Surfaces Facing Plasma 62 3.7.2 Blanket Structure 65 3.7.3 Experimental Blanket Modules 67 3.7.4 Toroidal Field Magnet . 68 3.7.5 Electrical Insulators 70 3.8 Environmental Considerations, Facilities, and Licensing 72 3.8.1 Environment 72 3.8.2 Facilities 72 3.8.3 Licensing and Safety 73 3.9 Method of Accomplishment 74 REFERENCES 73 vii

ABSTRACT

Scoping studies initiated at ORNL in August, 1974 are addressing basic questions: the objectives of the EPR, essential features, ranges of dimensions, research and development required to provide design input, and alternatives that must be pursued until information for firm decisions becomes available. Twelve task areas are: project definition, plasma engineering and physics, blanket and energy conversion, shielding, tritium systems, tokamak device engineering, tokamak support systems, materials and fabrication, design integration, assembly and maintenance, facility planning and project engineering, and program management. Initial results include delineation of major questions, identification of appropriate objectives and criteria, development of models and limited parametric studies of plasma characteristics, and preliminary conceptual design of an energy- recovery blanket with provisions for breeding experiments in interchangeable modules.

Keywords: conceptual design, controlled thermonuclear processes, energy, fusion, planning, plasma, power, tokamak, tritium BLANK PAGE viii

ACKNOWLEDGEMENTS

Many throughout the CTR community have given thought to what the first experimental fusion power reactor should be, and the work described here is, in part, a sifting and pulling together of the ideas of others. Initial assumptions as to the role of the EPR and its required timing are taken from DCTR planning documents. DCTR management has provided guidance as to the nature and scope of the studies at ORNL. One guideline has been to complement and corroborate EPR studies being conducted by the General Atomic Company and others, and to this end information has been exchanged with several external groups. Within ORNL there are others who are contributing besides those whose names appear at the heads of various sections of this report: M. Roberts is now managing the studies and the editor has had particularly helpful discussions with him, with D. Steiner and M. S. Lubell of the Thermonuclear Division and with J. L. Scott of the Metals and Ceramics Division. 1

1. INTRODUCTION

1.1 Background

U. S. CTR plans for the next ten years, both in plasma confinement and in fusion development and technology, have as their apex an Experi- mental Power Reactor. This EPR is seen as a D-T burning tokamak producing significant electrical power and beginning operation in 1985 (Ref. 1). In August, 1974, following the decision that the responsibility for the Tokamak Fusion Test Reactor would be assigned to Princeton Plasma Physics Laboratory,8 DCTR directed ORNL to redirect funds from the planned con- tinuation at ORNL of TFTR conceptual design3 toward "conceptual design and planning studies of a tokamak Experimental Power Reactor (EPR).'"' This document is the first formal report resulting from these studies. At the outset of the EPR studies at Oak Ridge, DCTR intended that they be done jointly with similar studies at General Atomic Company, evolv- ing from preliminary studies of a non-circular cross section FTR.s Although they were to be coordinated, studies at both locations were meant to be well-rounded and independent so far as evaluations were concerned. After considering the perceived needs of the EPR program and the anticipated participation of GAC, ORNL laid out a program of scoping studies and conceptual design beginning in FY-1975 and continuing through FY-1976. These plans were presented to DCTR management in meetings on September 12, Octo- ber 22—23, November 13, and January 7. During this period, the Electric Power Research Institute contracted with the General Atomic Company to conduct a two-year conceptual design study of an EPR, which is being done instead of the DCTR-funded studies originally envisioned. Meanwhile at Argonne National Laboratory, members of the Applied Physics Division independently produced a parametric study of plasma and related reactor parameters for a tokamak reactor experiment approximating the EPR.6 In the context just described, the studies at Oak Ridge are presently addressing the most basic questions related to F.11R: its function, possible ranges of dimensions, configurations and features, the research and development needed to support FPR design, and the alternatives that must be carried 2 along until information adequate for design decisions can be generated. These studies, which complement program planning by DCTR,7 are intended to provide a basis for decisions regarding the future EPR program. In particular they will lead into preliminary but comprehensive conceptual design of EPR in FY-1976.

1.2 Organization of Report

After tbJ.s introduction, the next major division of this report is a presentation of the scope, objectives, and or&*- ization of the ORNL studies. In the third major division, some basic considerations and preliminary but significant findings of the studies to date are presented. 3

2. SCOPE, OBJECTIVES, AND ORGANIZATION OF ORNL STUDIES

ORNL planning for EPR studies began with recognition of the unusual situation facing the EPR project: on the one hand we see that it is im- perative for the design process to begin immediately in order to have a chance of completing EPR by the target date of 1985, while on the other hand we recognize that some of the key information which will determine the EPR design features and dimensions will not be in hand for several more years. The urgency of developing fusion power and the importance to this development of timely completion and operation of a successful, relevant EPR are unquestioned. Preliminary consideration of an orderly progression to the U.S. goal of an operating demonstration fusion power reactor in the late 1990's plainly indicates that an experimental power reactor should begin operation in the mid-1980's. Furthermore, some of the key objectives and features of this EPR are evident at the outset: for example, superconducting magnets and recovery of D-T fusion energy at high temperatuu for electric power production. On the other band, because of existing large uncertainties in plasma scaling and the necessity for major technological advancements, a firm basis for some fundamental design choices can not be developed until after a normally arranged, aggressively pursued schedule for 1985 startup would demand that conceptual design and project authori- zation be completed. Obviously a program aimed at 1985 startup involves keeping open major options for several years. It is also obvious that even with a well-planned, vigorous program, successful completion by the target date depends upon favorable answers to physics questions and suc- cess in development efforts. Not only are there many important scientific, technological, and mana- gerial questions regarding EPR that remain to be explored, but it is con- ceivable that some questions have not yet been identified and plans made to generate their answers. In this light, the ORNL studies set out to define the basic questions, to assess the programs required to answer the questions, and to recommend a plan for proceeding expeditiously with the most meaningful conceptual designs possible under the circ-imstances. 4

2.1 Scope

The scope of the activity at ORNL through FY-1976 includes studies of basic design considerations, identification of programmatic needs, and initial conceptual design of a tokamak Experimental Power Reactor (EPR) that will serve effectively as a key element in the U.S. program for fusion power development. The purpose is to provide guidance for ongoing DCTR research and development programs and realistic target dates and preliminary cost estimates for use in program planning by DCTR.

2.2 Objectives in FY-1975 and -1976

The interdependence of the EPR with other parts of the overall program of fusion power development will be defined in terms of input required and output to be provided. Rational, recognizable objectives will be developed for the EPR in light of the needs of subsequent reactors for demonstration of technologies and resolution of physics questions. Information and experience prerequisites for the EPR design will be identified and any element not expected from presently planned programs will be pointed out. Basic considerations in EPR conceptual design will be elucidated. Where choices are.already clear, these will be made and justified. Where there is as yet insufficient basis for choice, the options that must be kept open pending further results will be clearly identified. (Examples of the latter are plasma shape and the utilization of divertors and/or other means of impurity control.) The sensitivity of EPR dimensions to plasma scaling assumptions, to the use of noncircular plasma, and to the inclusion of a divertor will be estimated and some reference dimensions will be proposed for use in components and systems studies. EPR requirements on support systems will be considered in view of the present state of the art and expectations from the development programs. Materials and concepts of blanket and energy conversion systems will be surveyed and a basis will be established for comparison and optimization in light of EPR objectives. 5

Results of the FY-1975 studies will be presented in an interim report at the end of the third quarter and a final report at the end of the fiscal year. In addition, an exchange of information will be maintained with the EPR conceptual studies being conducted by General Atomic Company for the Electric Power Research Institute and with other EPR studies supported by DCTR. Upon the basis of the FY-1975 results, conceptual studies at ORNL will be directed at one selected baseline design (with some evaluation of alternatives) that can be considered along with the GAC-EPRI conceptual design. The abject of the reference design study will be to produce a comprehensive, although preliminary, description of a self-consistent design. From this, a preliminary estimate of the costs of the EPR will be made and the requirements on various components and subsystems will be more clearly defined. Alternative designs will be pursued in sufficient depth to ascertain approximate differences in costs and development requirements.

2.3 Definition of Task Areas

For the purposes of planning the Oak Ridge program, the tasks fore- seen in the EPR studies were grouped in twelve task areas. The paragraphs which follow define the twelve task areas and discuss briefly the reasons for work in each area at this time.

2.3.1 EPR Project Definition

Definition — Bring into sharper focus the role of EPR in the U.S. program. Determine what technologies are to be tested or demonstrated, which physics questions are to be addressed. Identify performance criteria for the reactor and outline a proposed experimental program. Write all this up in a cogent document that can be widely circulated for discussion and refinement. Discussion — This task must be accomplished first. EPR must be relevant to subsequent reactors, especially the Demonstration Reactor Plant that comes next. Earlier research and development must not only be relevant to EPR but must constitute sufficient_J«&is~"~for its design. The 6 first step in defining EPR is, therefore, identification of the features of subsequent reactors that must be tested in EPR. Next is definition of foreseeable needs and an outline of the effort required in the next 5 to 7 years to provide a groundwork of adequate information and computational tools for the detailed design of the EPR.

2.3.2 Plasma Engineering and Physics

Definition — Considering extrapolation necessary from present knowl- edge, define different assumptions for plasma shape and plasma scaling and ranges of values for q, 3 , etc., that must be considered in EPR con- P ceptual designs until experiments narrow the possibilities. Cover the credible range of designs with a parametric study that produces dimensions and characteristics for different assumptions. For selected cases calculate current initiation, burn dynamics, fueling, impurity behavior, particle fluxes, etc. Provide criteria and input information for conceptual design of tokamak components and support systems. Discussion — Since plasma considerations dictate the size of the device and impose most of the requirements on the hardware, some tentative choices of reference dimensions and criteria must be made early to permit quantitative conceptual design studies to begin. Until PLT, PDX, and Doublet III operate, however,. options must be kept open and it will be necessary to select several appropriate sets of assumptions to serve as bases for different preliminary conceptual designs. 2.3.3 Blanket and Energy Conversion

Definition — Survey proposed fusion reactor blanket concepts in light of EPR objectives. Define EPR limitations and do parameter studies for purposes of comparison and optimization. For selected concepts, do conceptual studies emphasizing assembly and maintenance to achieve simple energy-recovery blanket with provisions for convenient test modules to investigate tritium-breeding systems. Discussion — EPR blanket requirements are unlike those of either the TFTR or subsequent reactors, which have been the subject of considerable study.. The special EPR considerations must be identified and the basis for design choices clearly delineated at the outset of the EPR design efforts. 7

2.3.4 Shielding

Definition — Evaluate suitability of various shielding materials for EPR: consider neutron and gamma attenuation, induced radioactivities, temperature limitations, assembly and maintenance, cost. For candidate concepts calculate energy deposition in shield and the neutron and gamma spectra emerging. Identify data that are inadequate and design procedures that need further development. Discussion—A comprehensive initial survey of materials is necessary; hopefully this will lead quickly to a few choice materials and arrangements. Attenuation and heating characteristics of these, in easy-to-use form, will permit preliminary conceptual designs to size shielding without repeated detailed calculations for every, variation .-'''This area is, of course, inextricably connected with blanket neutronic calculations. Close relation to fusion reactor technology development of data and codes is also evident.

2.3.5 Tokamak Device Engineering

Definition — Identify practical options and do preliminary design calculations for purposes of comparison for divertor, toroidal field coils, and plasma-driving system (ohmic heating magnetic circuit, plasma shaping and position control coils.) Discussion — Possible, divertors for EPR must be sketched sufficiently to estimate space requirements and effects on assembly and maintenance procedures and tools. Likely TP coil designs must be considered for different plasma configurations (circular or elongated, divertor or not). Options for plasma-driving system must be identified and basis laid for choices (superconducting coils or resistive coils, air core-or iron core, location relative to blanket, shield, TF coils). This should be done before choice of concepts for preliminary conceptual design.

2.3.6 Tritium

Definition — Determine amounts to be handled in primary system (plasma gas supply and recovery) and possible breeding experiments in special blanket modules. Establish criteria for safety and operational conveni- ence. Identify alternatives and develop conceptual flowsheets for the , 8 most promising. Identify further development work required for comparison and selection of equipment for EPR. Discussion — Early consideration of the type of system required for EPR is necessary for planning development as it is likely, due to special considerations, that the TFTR tritium system design will not be applicable to the EPR.

2.3.7 Tokamak Support Systems

Definition — These systems include neutral beam injectors, RF heating, diagnostics, vacuum systems, and power supplies. Consider EPR requirements in light of present state of the art and reasonable expectations from development programs. Identify most promising concepts for use in preliminary conceptual design and further development.

2.3.8 Materials and Fabrication

Definition — Select candidate materials on basis of possible application in future reactors, availability in time for EPR, suitability for EPR purposes, and cost. Identify unusual fabrication problems and development required. Discussion — Early identification of unusual needs in EPR is necessary, as the development and qualification of materials and fabrication techniques sometimes require years before acceptance for use under applicable codes.

2.3.9 Integration of Design

Definition — Coordinate design of all interrelated components and systems. In early studies, this involves recognition of conflicts, tradeoffs possible, and development of rational basis for optimization. Discussion — Only when all parties are made aware of how their parts of the facility must interact with others can they realistically do their job. Only when a rational basis has been developed can the optimum tradeoffs and decisions be made. This area is central to the production of a comprehensive, self-consistent conceptual design. 9

2.3.10 Assembly and Maintenance

Definition — Identify practical strategies for assembly and maintenance of radioactive portions of EPR. Conceptualize equipment, tools, and procedures sufficiently to permit evaluation. This includes viewing and manipulating equipment, disconnects of various kinds, transport devices, mobile maintenance work stations, and hot cells for equipment examination and repair. Identify special development requirements for remote joining and inspection systems. Discussion — The basic philosophy must be established at the outset and must imbue subsequent design to the end that maintenance of systems that have contained tritium or have become radioactive can be accomplished reliably, without excessive delays, and without excessive irradiation of personnel.

2.3.11 Facility Planning and Project Engineering

Definition — Define site, environmental, and safety considerations for an EPR. Identify anticipated procurement, fabrication, and transpor- tation problems and possible impact on project costs and schedule. Discussion — The outlook for procurement and fabrication times must be considered realistically along with constraints of the government bud- geting and review process in setting milestone dates that are sure to become widely publicized. A program must be laid out and experienced people must examine it to see if the target of 1985 operation can possibly be achieved by a conventional program or if a special national effort is required. Risks involved in proceeding before firm information is available must be assessed.

2.3.12 Program Management

Definition — Beside the management and administration of the current preliminary studies, this area includes consideration of the scope of the entire EPR project and identification of possible methods of accomplishment in terms of personnel requirements and organizational arrangements. Discussion — The magnitude and complexity of the EPR project will require participation of various laboratories, agencies, industries, architect-engineers, and constructors. A viable basis must be laid at the 10

outset; this involves examination of how the project should be structured 5 to 10 years in the future and establishment of as many as possible of the necessary relationships and critical staffing programs that can be developed and nurtured as time goes on.

2.4 Allocation of Effort in FY-1975

The allocation of effort to each of the task areas described in the foregoing section was made in light of the following considerations: • what ought to be accomplished in FY-1975 to permit E&R ^recon- ceptual design in FY-1976, • what basis already exists (related earlier studies, development experience, status of theory and analysis programs, project planning), • special emphasis in certain areas where appropriate (such as reactor technologies where, because of unique experience and capability, ORNL is counted on for the principal input to EPR), • direct use in EPR studies of applicable results being generated under separately funded programs at ORNL. The amount of EPR FY-1975 funds allocated to each task area and the principal participants are listed in Table 2.1. A breakdown of EPR effort and costs by organization and type of expense is given in Table 2.2.

2.5 Task Statements

This section consists of a statement of scope and a list of FY-1975 tasks for each task area, prepared by the person responsible for the area.

2.5.1 Project Definition (M. Roberts)

The definition of what should properly be included xn the project objectives and technical criteria for the Experimental Power Reactor involves the development of a consistent picture of the U.S. Tokamak program based upon existing materials at ORNL, GAC, and DCTR, emphasizing the goals of each of the various steps between today and commercialization. This 11

Table 2.1 EPR Study Task Areas, Allocation of FY-1975 Funds, and Staffing (January, 1975)

a EPR Funding b Task Area ($ thousands) Persons

1. EPR Project Definition 15 M. Roberts P. N. .Haubenreich D. G. McAlees D. Steiner Q 2. Plasma Engineering and Physics 10 D. G. McAlees F. B. Mam us G. D. Kerbel 3. Blanket and Energy Conversion 30 E. S. Bettis R. T. Santoro D. Steiner H. L. Watts 4. Shielding 15 R. T. Santoro 5. Tokamak Device Engineering 25 D. D. Cannon M. S. Lube11 6. Tritium 15 R. N. Cherdackd J. S. Watson S. D. Clinton 7. Tokamak Support Systems 5 G. Schilling 8. Materials and Fabrication 15 A. J. Moorhead J. L. Scott 9. Integration of Design 10 D. D. Cannon 10. Assembly and Maintenance 15 E. S. Bettis H. L. Watts 11. Facility Planning and Engineering 10 " E. H. Bryant 12. Program Management 60 M. Roberts P. N. Haubenreich Total 225

^Does not cover contributions of Thermonuclear Division personnel in closely related programs. Includes only persons presently participating. Does not include persons providing computational, drafting, or clerical support. CExxon Nuclear Co. ^Burns & Roe Co. 12

Table 2.2 EPR Study Manpower and Cost Breakdown for FY-1975

EPR costs Man-months ($ thousands)

Thermonuclear Div. 32a 74 Neutron Physics Div. 6 23 Chem. Tech. Div. 1 5 Metals and Ceramics Div. 3 15 Engineering 15 59

Subtotal UCCND labor + overhead 176

Consultants 10 Subcontracts 10 Travel 5 Materials 3 Computing Services 16 Technical Information Services 5

Subtotal 49

Total 225

"includes 13 man-months of other funded activities directly applicable to EPR task areas. 13

picture should be clearest near and around the EPR and the succeeding step, the Demonstration Reactor Plant. The intent of this phase of the work is to bring out the various underlying assumptions in the EPR efforts. Once this overall picture is under way, the requisite preliminaries such as missing elements of technology and science can more readily be identified and brought to the attention of the specialized technical staff. Addition- ally, the goals of the EPR need to be spelled out in detail with an experimental program for its operation. The end result of this work should be a concise written statement of the findings, iterated with as many people as possible. The EPR project definition wo«rk in FY-1975 involves the following tasks, performed in an iterative fashion. 1. Using D. Steiner's work0 and the programs outlined by DCTR,1'7 develop an annotated list of steps between today and commercialization. 2. Using the work of task areas 2—11, develop a list of missing pieces (development work for EPR) and the time scale for accooplishment. 3. Develop with the participants a set of goals for the EPR.

2.5.2 Plasma Engineering and Physics (D. G. McAlees)

The scope of the plasma engineering and physics task area is defined by the following five tasks. 1. Task; Determine the characteristics of alternative. EPR systems. Scope the systems in terms of size, power production, energy required to operate the device, etc. This can be accomplished using a static, time-independent model. Motivation: Establish the fundamental differences between driven, zero-power, and ignition devices. Expected Result: A more narrow range of parameters to be further considered as a reference design(s). 2. Task: Develop a spatially independent, time-dependent system model. The model will include the physics representative of the burning plasma core and the influence of the colder plasma which will exist between the core and the wall. Extend the system model to include overall operation. For example, injector efficiencies, 14

heat input to the coils, transformer performance, etc., will be coupled to the plasma operation to determine burn cycle limitations . Motivation; Follow system characteristics during operation to determine the performance limitations both from a plasma physics and engineering point of view. Permit various scenarios for operating the system to be analyzed, e.g., sequencing injection and fueling during the burn phase. Expected Result; A model which can simulate overall system operation and which has been developed in a manner suitable for up- dating as new information becomes available. 3. Task; Determine the neutral injection system requirements/parameters consistent with EPR systems. Consider beam energy, power, angles of injection, and required operating time compatible with the plasma burning strategy adopted. Motivation; Establish the type of injection systems necessary to support EPR operation for comparison with objectives of ongoing beam development programs. Expected Result; Necessary injection system design information. (Theoretical procedures are presently available to accomplish this task.) 4. Task: Analyze system startup. Startup includes formation of the plasma and the plasma current rise time. Determine energy requirements and the effects of various strategies of increasing the current to its final value. Motivation: Determine in as realistic a manner as possible the limitations on startup, the time required for startup and its effect on the overall burn cycle. Expected Result: An estimate of the energy and time required to start up an EPR size plasma. Preliminary evaluation of alternative startup procedures to determine the need for an expanding limiter, etc. 5. Task: Determine the plasma fueling requirements during the burn cycle. The rate of fueling required and the procedure (in terms 15 of timing) will be analyzed. (The mechanisms by which fuel is de- livered to the system is an open area for development; critical review of such mechanism is under way. Motivation: The fueling requirements for EPR must be defined to provide a goal for further work directed toward developing and designing a viable fueling system. Expected Result: Desired fueling rates for the EPR, including ranges of uncertainty and discussion of consequences of failure to achieve specified performance of fueling system. Critique of fueling mechanisms presently envisioned. (Continuing research on specific concepts for which results cannot be predicted.) 16

2.5.3 Blanket and Energy Conversion (P. N. Haubenreich)

This task area is directly affected by the choice of some key objectives for the EPR. Scoping studies in this area will assume that one primary objective of the EPR is to demonstrate reliable production of a significant amount of electrical power and that another is to provide for meaningful tests of candidate breeding blanket designs. The approach to meeting these distinct objectives will be to design the major portion of the blanket on the basis of power production alone, with provisions for breeding experiments in separate, relatively small sections that are interchangeable with modules of the standard design. During the scoping studies in FY-1975, possible choices of materials, configurations, dimensions, and operating temperatures for the mail.. part of the blanket will be surveyed. Preliminary evaluations of reliability, practicality of assembly and maintenance, costs, and attainable conversion efficiency will be made for a variety of concepts meeting basic EPR needs. Relevance to future reactors will be a strong consideration in comparing designs, but exact correlation of EPR features and operating conditions with those of later reactors will not be an absolute requirement. Sim- plicity and dependability will be other major considerations in choosing concepts for further consideration. For selected concepts, the crucial problems will be identified and preliminary conceptual design will be initiated to explore possible solutions. Pi-oposed concepts of tritium-breeding fusion reactor blankets will be reviewed and a concept of an experimental module will be devised with the goal of providing the simplest integral test of data and procedures used in breeding calculations.

2.5.4 Shielding (R. T. Santoro)

During EPR scoping studies calculations will be carried out using one-dimensional discrete ordinates methods to resolve the following: 1. the effectiveness of candidate blanket-shield materials in ab- sorbing energy and in attenuating penetrating radiation, 2. the elucidation of activation and heating problems associated with candidate blanket-shield configurations, 17

3. evaluation of neutron and gamma-ray fluxes :ui areas where radiation damage may be significant (i.e., in the first wall, the blanket structure, and electrical insulation), 4. the identification of potential problem areas such as penetrations, requiring more definitive calculations. 5. the integration of the neutronics calculations with specific requirements of other groups when possible.

2.5.5 Tokamak Device Engineering (D. D. Cannon)

This task in FY-1975 includes scoping studies which must be performed on several components before the initiation of a preliminary conceptual design effort. These studies will allow certain basic design choices to be made at the start of the ensuing conceptual design thereby allowing it to focus or the integration of the concepts for major components into a self-consistent design. Making the proper design choices requires that the designer have sufficient information to evaluate the alternatives available to him. This information includes such things as costs, energy requirements, remote maintenance and space requirements, component location, relative costs, operating characteristics, environmental effects, reliability and materials availability. Some of the scoping studies which must be conducted are: 1. Divertor — The inclusion of some type of divertor in an EPR is presently regarded as quite likely but not certain. Inclusion of such a device impacts the design of almost all the major tokamak components. A review of the existing divertor concepts and an assessment of their impact on the design of other tokamak components will be made. 2. Plasma Driving System — Several questions must be answered in se- lecting the plasma driving system concept such as the choice between resistive or superconducting coils, air core or iron core, and location of the windings. The criteria for making these choices include evaluation of such things as energy requirements, cost, stray magnetic fip.lds, and remote '...' maintenance. 18

3. Toroidal Field Coils — Although already the objective of a substantial development program, there are some key design questions specific to an integrated EPR plant which must be addressed before a conceptual design can be initiated. These include the question of coil shape and type of support system.

2.5.6 Tritium (J. S. Watson)

The objective of EPR tritium handling studies for FY-1975 will be to assess system requirements, to identify alternate techniques to meet these requirements, and to evaluate experimental development efforts which will be needed. The interdependence between tritium handling requirements and many features of the machine design will demand close interaction with other groups participating in this study. The areas to be studied this year include: 1. Supply and storage of tritium — metering, determining tritium content, method of storage, and associated safety considerations. 2. Removal of tritium from liner — pumping methods, pump location (general layout), methods of reaching storage conditions. 3. Removal of tritium from injectors — establish injector performance (efficiency), pumping load, pressure requirements, tritium content in injectors, comparison of pumping methods, etc. 4. Removal of helium and impurities — evaluate uranium beds and alternate techniques, establish needs for circulation, etc. 5. Tritium enrichment — establish concentration goals for all streams, compare options of using existing off-site facilities and new on-site facilities, and compare different techniques. 6. Containment and disposal of tritium wastes — secondary containment modules, atmosphere processing, storage and disposal of dilute tritiated water wastes. 7. Emergency considerations — emergency stack removal system, emergency maintenance, monitoring, etc. 19

2.5.7 Toksaak Support Systems (G. Schilling)

Scoping studies in this task area must identify these tokamak support systems that will be needed in the EPR, what their operating environments are likely to be, and the performance characteristics that will probably be required. Comparisons must be made with existing systems to determine the nature and extent of the development that will be necessary, whether it be technological evolution or major innovation. The support systems to be considered will include the following, arranged in order of increasing distance from the fusion plasma (and hence probably in order of decreasing complexity of adaptation to the EPR). 1. Support systems inside the first wall, close-coupled to the fusion plasma. There we may find RF heating structures and diagnostic current pickup loops. 2. Support systems outside the toroidal field coil structure but close-coupled to the fusion plasma through straight-through ports. These include laser, microwave, neutral particle, x-ray, neutron, and optical spectroscopy diagnostics, as well as neutral, beam injectors for heating, fueling, and controlling the reactor. 3. Support systems outside the toroidal field structure, not close- coupled to the fusion plasma. These include vacuum pumps and power, cooling, and control of diagnostics and injectors. Consideration must be given not only to the primary impact of the fusion plasma on the particular support system, but also to its impact on coupling structures and the secondary impact on the external environment because of the required penetrations through the shielding.

2.5.8 Materials and Fabrication (A. J. Moorhead)

The scope of the FY-1975 tasks in this area is as follows: participate in the selection of materials for EPR based on EPR conditions and requirements and present-day materials and fabrication techniques. Recom- mend methods of fabrication for such reference materials. Identify possible materials or fabrication problem areas and suggest research and development activities aimed at overcoming these problems. Where state-of-the-art materials and fabrication techniques are clearly inadequate, suggest potential alternatives and propose a course of action. 20

2.5.9 Integration of Design (D. D. Cannon)

Although the FY-1975 studies do not extend to include a complete conceptual design, some design concepts must be developed to determine space, energy, and access requirements and to identify conflicts, possible tradeoffs, and the necessary sensitivity studies to be completed early in conceptual design. This task area will include: 1. System Envelopes — Tentative systems envelopes will be developed for vacuum, refrigeration, and tritium handling system. The location of these systems relative to the tokamak will be studied. Approximate sizes for injectors, magnets, blanket, shield and plasma driving system must be estimated. 2. Design Choices — Where sufficient information exists, design choices will be made for system components. These may include only the selection of design criteria for a component or in some cases the choice may be. design -concept- re be employed in an EPR. 3. Identification of Required Sensitivity Studies .—Attempts to make design choices almost always raise questions as to the sensitivity of the resulting costs, size or operating characteristics to the selection of an alternative. Often the answer can be obtained quickly, but sometimes substantial sensitivity studies are required to evaluate fully an alternative. Required sensitivity studies must be identified early to allow time for decisions to be made before firming up a conceptual design. 4. Fusion Power Relevance — It is recognized that the resulting conceptual design must include many alternatives to be chosen later in the design process. However, there is a need to eliminate those alternatives which will not contribute to the development of fusion power in the future. This will require identification of those concepts which must be demonstrated in the EPR.

2.5.10 Assembly and Maintenance (E. S. Bettis, P. N. Haubenreich)

Scoping studies in this area should establish basic philosophies, identify practical strategies for the EPR, and conceptualize key features that may determine choice of strategy or requirements for long-range development. More specifically, in FY-1975 the following tasks will be undertaken. 21

1. General strategies — Once tentative choices have been made for the approximate size and principal features of the EPR, studies can proceed to define ways in which the machine could be designed for remote assembly, disassembly, and repair. (Alternatives, such as in-situ or hot-shop repair, will be identified for further evaluation.) The ways in which the optimum number of subassemblies is affected by considerations of trans- porting, locating, dimensional tolerances, and number of interconnections will be explored. 2. Transport and Location — The requirements will be scoped and practical means for moving large, heavy subassemblies and locating them with the accuracy required by assembly procedures will be studied. 3. Interconnections — Conceptual work will start on practical devices and procedures for making the numerous connections required in a large, maintainable, radioactive tokamak. This must go far enough to assure that the job can be done. Remote joining techniques meriting further development will be identified. 4. Observation and inspection — Capabilities and limitations of tele- vision and fiber optics for remote viewing will be defined, and applicability to various EPR tasks assessed. The same will be done for known techniques for remote, iprecision inspection. Recommendations for development will be made.

2.5.11 Facility Engineering and Planning (E. H. Bryant)

This task area is comprised of the following tasV,s. 1. Site Studies — The object here is definition of site requirements rather than specific geographic location. Important considerations will be location with respect to electrical power, cooling, water, and access to adequate shipping terminals. Plant electrical power requirements are expected to be in the 100—200 MW range. Individual components may weigh as much as.150 tons and range in size up to 40-ft dia. by 10 ft in width. 2. Environment and Safety — Investigate environmental and safety problems and identify those requiring special attention. Outline legal and regulatory requirements. 22

3. Industry Studies — Identify industrial suppliers for all of the major components of a tokamak power reactor. Evaluate the availability of materials and procurement durations. Also identify areas requiring development of industrial capability before the placing of orders. 4. Scheduling — Develop a PERT-type schedule for the EPR. Considera- tion will be given to the timing of expected scientific results and planned technology development and the ability of industry to respond. 5. Funding — Where possible, costs of the EPR components will be compared to fission power reactor components. Costs developed for the F/BX and the TFTR will be reviewed and compared to the EPR. From these reviews a general idea of the cost of the EPR will evolve by the end of FY-1975.

2.5.12 Program Management (M. Roberts)

This activity covers both the management of the study itself and the various possible schemes of EPR management. With respect to the study, a management plan must be spelled out and followed. With respect to the EPR management, various alternatives, involving industrial and laboratory participation, including GAC, architect-engineers, vendors, and constructors, within the local, 0R0, and DCTR systems need to be addressed and the merits presented. The following tasks are included. 1. Study plans need to be developed, approved by management, and implemented. 2. EPR management schemes need to be considered and the relative merits presented. 3. Staffing requirements need to be scoped and plans for achieving the required levels of experienced personnel at the appropriate times presented. 23

3. INITIAL OBSERVATIONS AND RESULTS

Some points about the EPR become evident as soon as one begins to consider what the EPR must do and what will be available in the way of information, components, and materials when it is designed and constructed. These points are set forth in this chapter, not necessarily because they represent any great advance but to make clear the basic requirements and assumptions upon which the conceptual designs and program plans will rest. In addition, our studies so far have begun to elucidate some of the questions that must be explored and the decisions that mu^t be made. These results, too, are presented in this chapter.

3.1 Definition of the EPR Project

P. N. Haubenreich

The Tokamak Experimental Power Reactor is both the focus of a broad program for the next ten years and a stepping-stone to the Demonstration Reactor Plant and the fusion reactors that will follow it. Definition of the EPR project therefore requires that we consider simultaneously what

informatio*n the EPR must produce (which determines its principal characteristics) and what information is necessary to design the EPR with con- it fidence (which affects the demands on earlier devices and programs). The necessary sequences and cross-connections among CTR program elements must be clearly identified and made known. 3.1.1 Fusion Reactor Features to be Included in EPR

The various conceptual studies of tokamak power reactors that have been done at Princeton,9 the University of Wisconsin,10 Oak Ridge,11 and abroad1a—13 have produced concepts that differ considerably in detail but which have in common several general features. These features are listed

•ft Because of the urgency of proceeding expeditiously with the fusion power program and the consequent compression of the EPR preparations, the realities of what can be accomplished in time to affect EPR design also affect the features that can be incorporated in the EPR. In Table 3.1. Alongside this list are the relevant features that should be considered for incorporation in the EPR. Although it is not included in the lists, another feature that the EPR should have in common with subsequent reactors is the general shape of the plasma, whether it be approximately circular or pronouncedly non-circular. Note also that mode of operation (driven, beam-controlled or ignited) is not identified ex- plicitly although it is involved in the statement regarding Q; this matter is discussed in Sect. 3.2. Another way of looking at the relevance of the EPR to subsequent tokamak fusion power reactors is to list the outstanding problems or questions with regard to these reactors and ask which of these will be addressed in a meaningful way in the EPR. A list compiled by an international workshop at Culham1'1 in 1973 is tha basis for Table 3.2. Fusion-fission hybrid systems15 are the subject of considerable interest at the present time, and, although the prospects of such systems based on tokamak technology are as yet unclear, the implications for the tokamak EPR must be seriously considered. Studies are being conducted for DCTR and the Electric Power Research Institute is initiating others. Among the EPRI ideas is that of a fusion device providing neutrons to a blanket that contains thorium to produce 233U (hopefully with little 333U) for use as UTGR fuel. (Development of a continuous process for removing protactinium and fission products from a thorium-bearing blanket is being pursued as a primary objective of the DRRD-sponsored Molten-Salt Reactor Program at Oak Ridge.)16 Other blanket concepts involve substantial fission power production in blankets containing 238U and plutonium. In considering any of these blankets for the EPR, the following question of basic philosophy is involved. Should the EPR exclude a blanket that produces fissions, 333U, or tritium (at least at first) to avoid possible interference with achieving the primary goal of advancing tokamak science and technology; or, if the ultimate application of tokamaks clearly involves such blankets, should the essential goals of the EPR include their demonstration? 25

Table 3.1 Some General Characteristics of Tokamak Power Reactors

Characteristics of Characteristics Turo-of-the-Century or Objectives Reactors of the EPR

1. D-T plasma D-T plasma

2. Tritium breeding blanket Tritium production in experimental modules

3. Heating by deuterium beam Heating by deuterium beam injection injection

4. Substantial electrical power Significant electrical power production production

5. Fusion energy multiplication Fusion energy multiplication factor sufficient for high factor adequate for significant plant efficiency electrical power

6. Superconducting toroidal Superconducting toroidal field coils field coils

7. Superconducting pulsed coils Either resistive or superconducting pulsed coils

8. Quasi-steady-state operation Quasi-steady-state operation (long pulses) (long pulses)

9. Divertor and/or other devices Divertor and/or other devices for impurity control for impurity control

10. Fueling system Fueling system

11. Parts subject to rapid radiation Inner parts designed for routine damage designed for routine re- replacement after becoming placement after becomirradio- radioactive active

12. All parts assuredly maintainable All parts assuredly maintainable with minimal radiation with minimal radiation exposure of personnel exposure of personnel 26

Table 3.2 Outstanding Problem Areas of Tokamak Power Reactors

Investigation or Problem Demonstration in EPR

1. System Startup (current rise, effects of transient Demonstrate, with larger plasma, sys- fields on superconducting magnets, tems and techniques designed and tested energetics of beams, atomic physics) in TFTR, TTAP and earlier devices.

2. Plasma Burn (ignition vs driven system, control, Investigate thermal and impurity be- impurity behavior, refueling, oper- havior. Test control system perform- ating strategy) ance. Demonstrate quasi-steady refueling of larger plasma than TTAP. Determine optimum strategy for reactors.

3. First Wall Protection (use oif screen or curtain to protect Demonstrate viability in combined radia- vacuum vessel walls, thermal design, tion, neutron and other particle fluxes impurity influx, surface erosion) of materials and geometries developed in TTAP and other devices.

4. Radiation Damage (neutron and gamma-ray damage in Measure fluxes, particularly around first wall, blanket, and insula- penetrations, to prove shielding de- tion) sign. Observe damage in high fields, sensitive materials.

5. Tritium Management and Control (recycle in primary system with maxi- Demonstrate performance and reliability mal recovery, contain to prevent of systems developed in Fusion Systems leakage or accidental release to en- Engineering Programs. vironment)

6. System Reliability (component reliability, accessi- Demonstrate long-term, high-availability bility, replacement, repair) operation (after shakedown). Demonstrate maintenance techniques and tools.

7. Environmental Effects (normal releases of radioactivity, Establish and emphasize acceptability of effects ok credible accidents) fusion power in course of full review process and operating demonstration. 27

3.1.2 EPR Operating Power Level

Preliminary thinking in DCTR and elsewhere about the purpose of the EPR has led to the view that it should produce several tens of megawatts of electricity. Assuming this gross electrical power and that the conversion efficiency is 20 to 30 percent, the average fusion power must be on the order of 100—200 MW(th) to achieve this goal. Further analysis is likely to bear out this early view, but the rationale for the choice of power level must be developed and described for review and criticism by the CTR-fusion power community. This will be a goal in FY-1975. Mean- while, in order to proceed with preliminary scoping studies, some assumptions will be made. Reference design values for fusion power vs time during operating cycles — both typical cycles and maximal cycles — are required to provide input for exploratory considerations of blanket, shielding, materials, maintenance, etc. The shape of the power vs time curve will, reflect anticipated plasma behavior, fueling operations or other control, and down time between burns (points discussed in Sect. 3.2). The choice of an average thermal power level to be used in preliminary studies is discussed in the paragraphs which follow. Among the requirements on EPR power that have been suggested at ORNL and elsewhere in the CTR community are the following, arranged in what may prove to be the ascending order of difficulty of attainment: 1. plasma power high enough to study alpha particle effects on plasma, 2. plasma power high enough to study burn dynamics and control, 3. radiation heating in toroidal field magnets intense enough to test heat transfer design, 4. neutron and gamma heating high enough fo~ demonstration of recovery of fusion energy in high-temperature medium, 5. heating intense enough to provide useful check of blanket heat transfer design, 6. significant electric power generation, 7. electrical energy breakeven, and 8. electrical power self-sufficiency. 28

Logically one should approach the setting of the power goal in the same way that he does the rest of the EPR planning and design: in light of the EPR's role in the progression of fusion experiments leading to a Demonstration Reactor Plant and ultimately to safe, reliable, economical power. At the outset it would seem that goal 4, 5, or 6 is likely to be the most reasonable objective. In any of these cases, the required fusion power would be more than high enough to achieve goals 1 and 2. (See Sect. 3.2.) Goal 3 can certainly be reached, but how well goal 5 can be achieved in EPR remains to be explored. Materials testing is not included in the list of goals that might determine the EPR operating power: the EPR may provide useful information or corroboration, but primary depen- dence will be on other sources. DCTR thinking of a year ago is reflected in WASH-1290, which says "The aim of the EPR would be to demonstrate significant power generation" and "electrical power production ... at many tens of electrical megawatts." In other places a goal of "net electrical power" has been mentioned, but the meaning of the word "net" is unclear, as in the past it has sometimes been used ambigiously by the USAEC in its application to fission reactor experiments. The term "electrical breakeven" has also been mentioned as a goal of EPR. These terms — "significant," "net," and "breakeven" — will be considered in turn. "Significant" Power — The dictionary definition of significant is simply "having meaning." Thus a reasonable interpretation of "significant power generation" in the EPR might be the production of electricity with equipment resembling that which will likely be used in the next-generation fusion power reactor. What is that? The question of suitable energy conversion performance in the EPR is affected by, but is not identical with the question of the best ultimate cycle. One line of thinking is that ultimately fusion reactor designers will seek high efficiency by the use of gas turbines, metallic vapor topping, etc. It seems, however, that when reliability, fuel cycle costs and capital costs as functions of thermal capability and plant thermal efficiency are taken into account, early fusion power reactors (immediately following the EPR) are likely to employ steam turbogenerators with moderate throttle conditions. If analysis for the 29

Demonstration Reactor Plant shows that this is true, then surely similar "conventional" equipment should be used in the EPR. Even it if should turn out that all fusion reactors after the EPR will have very high- temperature thermodynamic cycles, one might choose in EPR, for the sake of reliability, to use a moderate-temperature steam cycle to generate electricity. It seems justifiable to say that the EPR is generating ' significant1 power if it is producing as much as early fission reactors that are regarded as successful power demonstrations. Key fission power experiments preceding true commercial reactors are listed in Table 3.3. (Although representing only half or so of all the reactors of their era, these are the ones that were most heralded and are best remembered.) Aside from the 90-MW(e) Shippingport reactor, the highest electrical power of any listed is 22 MW(e). Note that some of the reactors that the AEC classified as "experimental power reactor systems" did not generate electricity at all.17 About all that can be said from this comparison is that if the EPR makes some tens of electrical megawatts, it will use generating equipment that is in the size range not only of the reactor experiments but also of the early reactors (such as Shippingport, Piqua, and Elk River) that utilities operated primarily for the power they could generate. (AEC paid for construction of the reactors in the interests of reactor technology development.) "Net" and "Breakeven" — The word "net" in the context of a power station means that which is left after the station requirements are deducted from the gross electrical production. In the tokamak EPR plant, there are wide cyclic variations in both the electrical power requirements (for plasma-driving system and injectors) and the thermal power being produced by the fusion reaction. It is necessary to be specific about the power or energy goals and "net" should not be used without explicit definition. The condition that might be called "plant energy breakeven" is a clearly recognizable point (and more precisely defined than "significant power"). This means that over a period of one or more tokanak cycles (burns) the total electrical energy flowing out of the plant equals the electrical energy that flows in. Under this definition, during the parts of the cycle (plasma initiation and heating) when electrical requirements 30

Table 3.3 Power Output of Experimental and Early Central-Station Power Reactors

Power Name Type Start''-- Plant, Reactor, Shutdovn net MW(e) MW(t)

Experimental Power-Reactor Systems

EBR-1 Experimental Breeder LMFBR 1951-64 0.15 1.4 Reactor No. 1

HRE-1 Homogeneous Reactor aqueous 1952-54 0.14 1.0 Experiment No. 1 homogeneous

EBWR Experimental Boiling boiling 1956-67 4.0 100 Water Reactor water

VBWR Vallecitos Boiling boiling 1957-6.3 5.0 33 Water Reactor water

SRE Sodium Reactor sodium- 1957—64 5.7 20 Experiment graphite

EGCR Experimental Gas- gas-cooled 22 84 Cooled Reactor

EBR-2 Experimental Breeder LMFBR 1963— 16.5 62 Reactor No. 2

EOCR Experimental Organic- organic- 40 Cooled Reactor cooled

MS RE Molten-Salt Realtor molten-salt 1964-69 8 Experiment fuel

UHTREX Ultra-High Temp. helium-cooled 1968-70 Reactor Experiment

Central-Station Electric Power Reactors

Shippingport pressurized 1957- 90 505 water Elk River boiling 1962-68 22 58 water Piqua organic 1963-66 11 45 moderated Bonus boiling nuclear 1964—68 16 50 s uperheat Extracted from USAEC, Nuclear Reactors Built, Being Built, or Planned, TID-8200-R30 (June 1974). 31 peak, the external power grid could supply energy to the plant if over the rest of the cycle an equal amount of energy flows out. Public description of an EPR facility operating in this fashion would have substantial psychological impact. One might wish to go further and visualize an EPR facility that had the capability of continuing full operation when disconnected from any external power network. Although the idea has some appeal, it is of dubious value. In comparison with the "plant energy breakeven situation" the "self-sufficient" facility would have to have either a larger turbogener- ator (with suitably fast response to load changes) and/or more electrical storage capacity ir«. order to meet peak demands (from plasma driving system and injectors) without outside aid. There is no practical advantage: the reliability and capability of major power grids (such as TVA) are such that it seems unlikely that the ability to continue full operation when disconnected would be exercised. The only possible justification is on the basis of greater psychological value that might attach to such "electrical self- sufficiency." It does not seem that this would be worth the additional expenditures for self-sufficiency. Thermal Considerations — The most demanding heat transfer situations in the EPR will undoubtedly be associated with some of the surfaces exposed to the plasma (the limiters, the first wall, and divertor surfaces). Although this is true, and these spots must therefore be carefully designed, it seems inappropriate that the reactor design power level be determined on this basis. Superconducting coils, although tested under otherwise realistic tokamak conditions in TTA, will be subjected to substantial radiation heating for the first time in the EPR. (Development tests could include simulated radiation heating.) The EPR coil shielding and cooling must be conserva- tively designed so that the coils do not eosae close to quenching due to radiation during normal operation. Clearly a tradeoff can be made between shield thickness (and materials) and coil cooling capability. From the standpoint of magnet development it may be desirable to perform tests in which the heating in the EPR coils is allowed to increase in order to determine the actual capability of the cooling system. This would require 32 an increase in heating by a factor of two or more (the safety margin during normal operations)• Since other considerations may rule out increasing the fusion power this much above the normal level, the increased heating in the coils will probably have to be accomplished by removing several cm of shielding in a strategic location. By simply adjusting the thickness of the EPR shield, one could easily produce heat generation rates in the coils equal to any expected in future reactors; this is true almost regardless of what the EPR power is. In short, the point is that the power for which the EPR is designed will not be determined by the radiation heating in the coils. Blanket heat generation and removal in EPR will be of great interest because of their relevance to design of later reactors. Regardless of the form of the EPR blanket, the higher the power density, the more valuable will be the experience. It appears that it will be difficult to get EPR * blanket power densities up to the range of high-performance reactors. Thus blanket heat removal considerations constitute a pressure to increase the EPR design power, but do not define a threshold. Materials Considerations — Materials considerations are not likely to set limits on the EPR design power. At any reasonable power, the neutron fluxes will be high enough to affect various components, but judicious selection of first wall and blanket structural materials will minimize the constraints on EPR design by materials considerations. The desirability of obtaining useful irradiation data from the EPR is another factor that tends to push the design power up, but does not define a reasonable threshold power. 3.1.3 Goals of Long-Term Operation

In order to be a convincing demonstration of growing maturity in the fusion power effort, the EPR must operate quite safely and reasonably reliably for a substantial period of time. Safe operation can be defined as

A basic dilemma in experimental reactors, which must be explored in the EPR studies, is that the device must be large to meet some essential requirements, but the power must be small relative to power reactors to hold down costs; the result is low power densities. A set of credible EPR dimensions are RQ = 7 m, r^ = 2.5 m, P = 150 MW and Uf = 20 MeV/fusion. In this case the neutron wall loading is 0.15 MW/m2. For comparison, the neutron wall loading in the Princeton reference reactor (MATT-1050) is 1.8 MW/m2. operation with no unusual radiation exposures to operating or maintenance personnel, no injuries related to che peculiar features of the plant, and no incident that is of concern from the standpoint of the health and safety of the public. What constitutes satisfactory reliability and duration for an operational demonstration requires some consideration. One yardstick of reliable operation is the record of present-day commercial power plants. Plant availability factors for large (>600 MW(e)) plants in 1972 and 1973 averaged 74% for fossil-fueled plants and 73% for nuclear plants.18 More pertinent to the tokamak EPR are the records of early experimental fission power reactors. Table 3.4 lists plant capacity factors achieved by typical experimental power reactors and the total equivalent full-power hours of operation before the conclusion of their experimental program.19 It would appear that a reasonable design basis assumption for the duration of EPR operation would be two equivalent full- power years (17,500 EFPH). Unofficial targets for reliability might be something like 65% availability (after a shakedown period) and perhaps 50% capacity factor over a selected one-year interval. Because of the experimental nature of the EPR, it appears inappropriate to publish quantitative goals for availability and duration of operation. The figures suggested above satisfy a need for assumptions or targets within the project.

3.1.4 Required Input from Research and Development Programs

The various items of information and the experience that will be necessary for confident design and construction of the EPR will be discussed under each task area. To indicate the extensive inter-relationship of the EPR design effort to various programs, Table 3.5 lists items that will certainly be needed. How the EPR conceptual design should or could possibly shape the specific goals of the various devices and programs is an important management question. The impact of late availability of information on the manner in which the EPR design effort is organized and prose- cuted must also be weighed. 34

Table 3.4 Duration of Operation and Capacity Factors'2 Attained by Experimental Fission Power Reactors

b Startup- Total Max. Ann. Capacity Reactor Type e Shutdown EFPH Factor, %

EBR-1 LMFBR 1951-64 5,504 19 (1953)

HRE-2 aqueous 1957-61 3,100 15 (1959) homogeneous

SRE sodium- 1957-64 8,140 26 (1963) graphite

EBWR boiling water 1956-67 11,164 41 (1958)

MS RE uiolten-salt 1965-69 13,172 65 (1967) fuel

^Annual capacity factor is defined here as the ratio of energy produced in a calendar year to that which would have been produced if the reactor had operated at rated power for the entire year. See Table 3.3 for full name of reactor and rated thermal power. Equivalent full-power hours over the operating life of the reactor, equal to the total fission energy produced divided by the rated power. 35

Table 3.5 Input Required for EPR Design and Principal Sources

Source of Information Topic a or Experience

1. Plasma physics scaling PLT, TTAP, TFTR

2. Plasma configuration (non-circular) D-III 3. Plasma current initiation and control PLT, D-III, TTAP, TFTR 4. Injection heating NBD, PLT, D-III, TTAP, TFTR 5. Handling of large energies in plasma PLT, TTAP, TFTR 6. Impurity control a. behavior (in long pulses) TTAP b. divertor performance PDX c. efficacy of other measures ISX, D-III, TTAP 7. Alpha particle effects Theory, TFTR 8. Fueling system a. plasma requirements (in long pulses) TTAP FSE b. practical methods SMDP, TTA 9. Toroidal field system (superconducting) Theory 10. Burn dynamics FSE 11. Tritium handling in tokamaks FSE 12. EnergKE yint conversioo usefuln heat (14-Me) V neutron 13. Blanket materials for tritium production FSE, Materials or energy multiplication 14. Tokamak Shielding FSE, TFTR

Letters refer to elements or subelements in DCTR Tokamak R&D Plan as follows: PLT = Princeton Large Torus, TFTR = Tokamak Fusion Test Reactor, D-III « Doublet III, TTA = Technology Test Assembly, TTAP = Tech- nology Test Assembly with Plasma, PDX « Poloidal Divertor Experiment, ISX = Impurity Studies Experiment, SMDP = Superconducting Magnet Develop- ment Program, NBD = Neutral Beam Development, FSE = Fusion Systems Engi- neering. 36

3.2 Plasma Physics and Engineering * D. G. McAlees

As indicated in the preceding section, the EPR must be capable of producing deuterium-tritium fusions at a rate equivalent to more than 100 MW of thermal power for a substantial fraction of the time. Beyond this rudimentary definition of requirements on the plasma, there are many outstanding questions that must be answered rather early in the EPR design process: does the mission of the EPR require ignition? Will a beam injection controlled device provide the information and experience that is sought? How will the characteristics or performance of the power conversion system and plant electrical load affect the demands on the plasma? Of course, the generally recognized uncertainties in numerous plasma physics assumptions relative to safety factor, beta poloidal, confinement time scaling, etc., are faced in the EPR design and will not be conclusively resolved for some years to come. The purpose of scoping studies in FY-1975 is to determine the sensitivity of system operation to changes in key parameters (not limited to the plasma) and to assess self-consistently the suitability of various system concepts. With a 1985 completion date for the EPR as a target, it will be necessary to proceed for the next several years with concurrent design efforts on those different concepts most likely to be proved best by experiments yet to be done. This status report outlines major problem areas being pursued in FY- 1975, the methods of analysis, and examples of results to date. Although parameter surveys are presently underway, the presentation here centers around models which have been developed, with only typical results given.

3.2.1 Guidelines for an EPR

The EPR must produce tens of electrical megawatts. However, design criteria for the plasma itself must be established. At the outset, only the following general guidelines are evident.

Exxon Nuclear Co., Inc. 37

(1) The EPR plasma operating characteristics shall be enough like those envisioned for full-scale fusion reactors to yield information that is sufficient for confident design of the demonstration reactor plant. (2) The thermonuclear power produced shall be of the same order as * the power required to operate the system.

3.2.2 Sources of Design Information Tne uncertainty in predicting the operating characteristics of large thermonuclear grade plasmas based on present understandings is great. The fundamental concern in such an extrapolation is confinement time scaling. Confinement time scaling laws have evolved over the years20 both empirically and from theoretical predictions but their applicability to EPR cannot be assessed at this time. Similarly, assumptions and extrapolations in impurity behavior, impurity control schemes, fueling, and other areas of plasma technology are required to permit an EPR conceptual design to proceed now. Necessary experimental data in key problem areas will become available throughout the 1970's and early in the 1980's and will support EPR work. Table 3.5 shows a list of design areas relevant to EPR and power reactors and the anticipated U. S. experiments which will provide key design data. Of course there are no firm boundaries implied and many experiments will contribute in ways not listed. In addition to these more global problems facing fusion power devices in general, specific concerns relative to an EPR which must be addressed in conceptual design studies include the desirability of ignition vs a beam-injection-controlled (BIC) device, duty cycle required, and operating strategies which will produce the necessary power profiles.

This criterion is intentionally vague since detailed system energy balances are required to determine the plasma size necessary to attain a specific objective such as net electrical power production. This correlation is part of the study. 38

3.2.3 Time-Independent Model

To compute the dynamic characteristics of a particular EPR plasma, some assumption for the confinement time scaling must be made. However, if a portion of the burn cycle is to take place near steady state, a tine- independent analysis of the operating point is possible and useful. This approach is being taken in our study since a great deal can be learned about the system in terms of NT (density-confinement time product). This is attractive since the next step, associating a system size with a particular NT, involves the uncertainty of confinement time scaling. A power balance utilizing spatially averaged plasma parameters is a suitable model for the time independent analysis. The power balance developed includes diffusion losses, bremsstrahlung and line radiation losses, neutral beam injection power and thermonuclear power production. The thermonuclear power produced results from both fusion events in the bulk or Maxwellian background plasma and fusion events which occur in collisions between fast injected particles and the background. The implications of operating philosophies ranging from two-component-torus systems (low NT) to ignition systems (high NT) can be illustrated with this model. System sensitivi- ties to changes in operating parameters can also be examined in terms of NT. The utility of the model will be in surveying large parameter fields. This is underway. Figure 3.1 is typical of the results obtained from the static model. For the plasma characteristics shown on the figure note that at low NT (1013 cm-3 - s) the system operates as a two-component-torus. In all cases represented in Fig. 3.1, the fusion power density has been optimized with respect to deuterium-tritium composition in the background plasma.

Thus Np ranges from zero at lo\* NT to ND = N^ at ignition. In the TCT mode the beam power density, P^/VJ required to sustain energetically the system is large, due to the relatively low confinement time implied. The fusion power density produced, P„/V, is solely due to beam plasma fusion M events, as shown by the Maxwellian to total fusion (P_ /P_.) curve. Also, C r Q S Pp/P^, is approximately equal to F, the beam multiplication factor. 1u 3 At ignition, NT = 6 x 10 cm" -s, = 0, Q=» AND AN fusion power is produced in the background plasma. One final observation from Figure 3.1: in the present case requiring ignition, NT = 6.0 x 10ll* cm"3 - s, 39

ORNL—DWG 75-21W

1.0 10

0.8 p^/f} 0.6 Q. Eu- a. 0.4

0.2

1.5

S -0 I>- UZl yjyv Q CC0. 5 ai § a.

10'3 10" 10« /

A - 3, Bo = 40 kG, q = 3.0, T = 10 keV, = 150 keV, F = 1.7, Z » 3, N. ./N = 0.01. eff lml p 40 or requiring that ^ 90 percent of the total fusion power be produced by the background plasma, NT = 2.5 x 101I* cm-3 - s, necessitates Nx's that differ only by about a factor of 2. If Nx scales rapidly with size, this could suggest similar size plasmas to achieve either goal. The effects of impurity composition, fuel mixture, beam energy, field strength, etc., on this and other characteristics are being assessed using the static model.

3.2.4 Time-Dependent Model

The static model permits an analysis of the steady-s';ate operating point, but a dynamic treatment is required to determine how a given system approaches the operating point and under what conditions it can be energetically maintained there. The time-dependent model which has been developed at ORNL also utilizes space-averaged plasma parameters but follows their evolution during operation. The emphasis in this model as it is further refined will be on its inclusion of system parameters where the plasma represents only one component. For example, injection system energy requirements, fueling needs and detailed plasma current driving system characteristics must be included and an appropriate system "Q" computed under various conditions. At present the dynamic model includes electron, deuteron, triton and alpha particle and energy equations, the effects of high-Z and low-Z impurities, radiation, convection and conduction energy losses, electron-ion thermalization, neutral beam heating and fusion power production. System operation is followed from initial conditions of low temperature 100 eV), full density, and full plasma current. The detailed analysis of attaining these conditions initially is beyond the scope of this code and, in fact, is an area of active research in itself. Typical results for a system with major and minor radii of 6 and 2 13 3 meters, respectively, ZEFF ^ 2 (Z^ = 6) , N = 6 x 10 cm" , q = 3, B^ (axis) = 40 kG, and 50 MW of neutral beam heating are shown on Figs. 3.2 and 3.3. The treatment of confinement time scaling will be discussed in detail in a subsequent EPR report, but it should be noted here that conduction and convection times include the pseudoclassical, neoclassical 41

Fig. 3.2. Ion Temperature, Particle and Energy Containment Times vs Time. (R » 6m, a • 2m, 50 MW neutral injection.) 42

ORNL—DWG 75-2162

TIME (sec)

p ? P vs Time R = 6m Fig. 3.3. Power Output and Q = ( out ~ in^ in - ( > a = 2m, 50 MW neutral injection) 43 and trapped particle regimes, with trapped particle effects taken to be a factor of 2 less severe than predicted by the formula presented by the U.S. low-beta review panel in WASH-1295 (ref. 20). Also, the figures reflect the fact that cold fueling is included in the analysis and permits steady-state conditions to be maintained after ^ 6 seconds. The confinement time curves depict the usual shape as the system passes through the two trapped electron regimes and is driven into the trapped ion regime by the continuous injection at a level of 50 MW. A treatment of Q representative of a power-producing system is being formulated. Figure 3.3 shows a thermal Q which is computed from the thermal power available from the system and the thermal power input to the plasma. Negative Q's occur when the input power is primarily being stored in the plasma during the heating phase. Neutral beam efficiencies are not presently taken into account so that at steady state Q % 1 since the injection power is 50 MW and 47 MW of fusion power is produced. Note that this system will produce PF > 60 MW if operated with 50 MW of deuterium injection = 150 keV) and a pure tritium target. In conjunction with the static model, the dynamic model is being used to conduct a more con- clusive parameter survey. 44

3.3 Blanket and Energy Conversion

E. S. Bettis P. N. Haubenreich

Numerous concepts have been advanced for the materials and mechanical arrangement of blankets of fusion power reactors. Generally, however, they are conceived for future reactors that have requirements for highly efficient power production, tritium breeding, and (in some concepts) fission heat generation in the blanket. The requirements that have been established for the Experimental Power Reactor are different from those of the ultimate reactors, so the first step in the scoping studies is to establish blanket design criteria that are consistent with the overall purposes of the EPR.

3.3.1 Conceptual Design Criteria

In order to attain a reasonable energy conversion efficiency in the EPR, che blanket must absorb a fairly high fraction of the neutron energy which constitutes about 80% of the primary fusion energy. The absorption of this energy must raise the temperature of the blanket high enough for efficient use of the blanket coolant in a heat engine to produce electrical power. Heat generated in the blanket must go predominantly into the coolant, with only small fractions escaping to the components adjoining the blanket. The high-temperature blanket region, because of its more intense heat generation and concomitant cooling provisions, will probably be more expensive and less effective in attenuating neutrons than a low-temperature region optimized for shielding. Therefore conceptual design should consider providing the required total attenuation by including a shield region outside the blanket. When EPR power operation begins the blanket will quickly become highly radioactive due to neutron reactions; thus reliable, tested, completely remote means of assembly and disassembly must be provided. The blanket will will be so massive that modular construction will be essential. Design of the blanket modules must be such as to facilitate to the highest possible degree the remote handling of these units. This remote operation involves mechanical clamping, welding of components in difficult geometries and 45 cramped quarters, making coolant connections, and similar types of operations. The reversal of these operations must also he possible for disassembly and removal of the modules. The first wall of a full scale power reactor blanket will undergo the most severe radiation damage, so it will be desirable that this first wall be replaceable without replacing the entire blanket. This of course will involve making the wall and its coolant header detachable from the surrounding blanket segments by remote means. Because it is expendable, this wall should be designed with economy in mind. Since in EPR the radiation damage is not sc. severe, the EPR blanket may not need to have the replaceable inner wall. At least one such segment should be included, however, as a prototype for a power reactor blanket. It is not required that the EPR breed tritium. Since a thermonuclear power economy based on the D-T cycle demands that tritium be produced in commercial fusion reactor plants, however, the blanket design for the EPR should permit the inclusion of tritium production experiments without a major redesign of the blanket. The blanket modules should therefore be designed so that tritium-producing modules with separate cooling systems can be substituted for the standard modules at a number of points. Insofar as possible consistent with reliability and economy, the design of the EPR blanket should be extrapolatable to meet full power station requirements. As an example, helium would be preferable to water as a coolant, although the EPR would probably use lower pressures than in a full scale plant.

3.3.2 Candidate Materials

Different types of blanket materials must be evaluated in light of the EPR requirements. For the main part of the blanket, some combinations of

BfcC, graphite, and stainless steel in the form of solid absorbers appear most promising. Optimum ratios of these absorbers and their relative dispo- sitions within the blanket as well as the total blanket thickness are being determined. For the tritium-producing modules, solid materials to be considered are LiA103, beryllium, and graphite. In addition some static, canned, liquid absorbers will be evaluated. Liquid absorbers capable of 46 slow circulation through the blanket may have certain advantages, especially for the production of a33U with low 232U content. By circulating a thorium-bearing molten fluoride salt outside the blanket, Pa could be quickly removed thereby reducing greatly the fission product inventory in the blanket. Helium at fairly high pressure is one of the most likely coolants for the main part of the blanket. It has acceptable heat transfer properties, does not parasitically absorb neutrons, and facilitates removal of tritium. (Small (ppm) amounts of water and/or oxygen mixed with the helium will sequester the tritium and can be processed out of a side stream.) For the experimental modules, the coolant might be either helium or a liquid metal, as proposed in various power reactor concepts. The candidate structural materials for the EPR blanket are discussed in Sects. 3.7.2 and 3.7.3. Water is not generally regarded as a likely candidate for fusion reactor blanket cooling, but could be considered as a possibility. If a thermodynamic fluid such as a freon for instance is considered for use in a low-temperature heat engine, water at low temperature could be used as a blanket coolant. At least a brief look should be taken at this possibility.

3.3.3 Outstanding Problems

The blanket is one of the components that presents major remote assembly and disassembly problems. Either the entire blanket or the first wall will have to be replaced several times during the lifetime of a full scale reactor. This may not be an absolute necessity in the EPR, but the EPR blanket must nevertheless be designed for remote handling and maintenance. The blanket segments must be small enough to be transported and accurately positioned. Means of clamping between segments to provide mechanical strength and of welding between segments to provide a vacuum seal must be conceived, evaluated, and developed. Provisions are also needed for the attachment of penetrations, interconnections between segments and the various coolant and electrical sources. After a blanket segment has been conceptualized, various analyses must be made of stresses, coolant pressure drop, and heat transfer. Such 47 analyses must be done during the scoping studies in at least sufficient depth to ascertain that the design concept is viable.

3.3.4 Fiogress

One type of blanket has been conceptualized that is relatively simple, inexpensive, and adequate for the EPR conditions. It is not considered satisfactory for a higher power tokamak reactor because the inner wall is not independently replaceable and the volumetric flow of the relatively low pressure (10 atmospheres) helium coolant that is used would require excessive pumping power. In this EPR concept the number of blanket segments is three times the number of toroidal field coils (72 5-degree segments for the case of 24 coils). The segments are joined to form the toroidal vacuum chamber. As- sembly involves insertion of a segment between TF coils, rotation into position, clamping and seal welding to adjacent segments. The absorber material is in the form of spheres, with helium flowing among them. Each segment has a helium inlet and outlet which are connected to manifolds running around the machine. For cooling purposes each segment is divided into four chambers. Helium enters the inlet plenum, flows through distribution holes into one sphere-filled chamber, across the spheres and into coolant passages adjacent to the first wall. The downstream end of each coolant passage communicates with the return chamber which also contains spheres. The coolant flows over these spheres, into the collecting plenum and thence into the helium outlet manifold. The helium pressure is kept down so that the segment walls can be of reasonable thickness. In the EPR the neutron current through the inner wall is low enough that the volumetric heat generation in this wall is tolerably low. In order to avoid serious thermal stresses in the boxlike structure, however, it will be necessary to limit the difference between inlet and outlet gas temperatures, possibly to no more than about 100°F. There is reason to doubt that the foregoing concept (where the shell of the segment constitutes the pressure vessel) can perform adequately in higher powered reactors; projections are that it cannot. Thus, a second concept is being considered for the EPR, in which the gas is contained in 48 tubes capable of high-pressure operation. In this tubular concept the inner wall of the segment is made up of coolant tubes running circumfer- entially around the inside of the segment. The helium coolant is at a pressure of 50 atmospheres. Between the tubes and the plasma is a thin woven graphite curtain. Graphite slabs approximately 3 in. thick are placed on the other side of the tubes next to the blanket wall. This entire assembly of tubes, graphite curtain and slabs is separate from the blanket segment and can be removed from it by cutting the helium inlet and outlet headers. The blanket itself is composed of cylindrical elements of canned absorber inside container tubes, with gas flowing in the annulus between the tube and the canned absorber. These cans are located with their axes parallel to the torus and the blanket is four cans thick in the radial direction. The inner layer of cans is welded together to form the vacuum wall. 49

3.4 Neutronics and Photonics Calculations

R. T. Santoro

3.4.1 Criteria for Calculations

Neutronics and photonics calculations are being used in studies directed toward optimum selection of materials and arrangements to meet the EPR requirements on blanket and shield. Factors being considered include performance, practicability, and cost. The EPR blanket oust absorb a large fraction of the energy of the fusion neutrons and secondary gamma rays so as to raise the temperature of the blanket coolant high enough to permit efficient conversion to electric power. The shield surrounding the blanket must provide the additional attenuation required for the protection of personnel and equipment in the vicinity of the reactor. Evaluation of candidate designs involves calculation of heat generation and radiation damage fluxes in the blanket, shield, and adjacent sensitive components. For each case considered, spatial distributions and integrals of energy deposition throughout the blanket and shield by neutrons and by photons must be calculated. The radial and energy-dependent neutron and photon fluxes must also be calculated for use in evaluating radiation damage effects. Heat generation in the inner parts of the shield must be calculated with sufficient resolution to permit conceptual design of the special cooling provisions required for those bodies in which heating is especially intense.

3.4.2 Methods of Calculation

The blanket and shield neutronics and photonics calculations are being carried out using the one-dimensional, discrete ordinates code ANISN. Coupled neutron and gamma-ray groups (100 n - 21 7) generated from the ENDF/B4 library are being used to calculate the flux distributions in the blanket and shield. Energy deposition in the components are being estimated using neutron and gamma-ray factors generated by the codes MACK and SMUG, respectively. 50

3.4.3 Progress to Date

At the time these calculations ware initiated, an up-to-date, coupled n-Y cross-section library adequate for fusion reactor calculations did not exist. A 121-group (100 n - 21Y) cross-section library has since been generated for materials of interest to the EPR (and other fusion reactors) from the ENDF/B4 library. A report summarizing these cross sections and their availability to other CTR researchers is being prepared. Neutron and gamma-ray kerma factors have also been prepared for all of the materials on the cross-section tape in the corresponding group structure. 51

3.5 Magnet Considerations

SCMDP Staff*

There are clearly compelling reasons why the toroidal field coils in the EPR must be superconducting. The first reason is power consumption, which is prohibitively large for resistive coils of the size and field required for the EPR. For example, a water-cooled copper toroidal magnet system with a bore of 6 to 10 m, aspect ratio of 2, and maximum field of 8 T would require approximately 500 to 850 MW in steady operation. Pulsed operation of the toroidal field in the EPR is not acceptable because the basic objectives of the reactor require quasi-steady state operation of the plasma. In any event pulsed TF coils for the EPR would require extremely large and expensive energy storage and power supply systems. (The 3.2-m bore toroidal field system in TCT reaches a peak demand of 329 MW and consumes 2966 MJ during a pulse.) The second reason for superconducting TF coils in the EPR is that they will be a necessity in the Demonstration Reactor Plant and subsequent fusion reactors that must produce net electricity at a reasonable plant efficiency (even if the EPR does not). Prudence dictates that superconducting toroidal magnets be proved under realistic tokamak conditions even before their incorporation in the EPR and certainly their proof-testing must not be done in the even larger and more expensive reactors following the EPR. The choice of the best shape for the toroidal field coils cannot be made at this time. Beyond the obvious reason that the shape of the EPR plasma has not yet been decided, further calculations and experiments are required to elucidate such questions as lumped Vs distributed structure, the reduction of bending moments and peak stresr-es in an oval coil of finite cross section for a toroid containing a discrete number of coils, the complexity and fabrication complications for non-circular bobbins and structures compared to circular colls, and the different field distribution

Super-Conducting Magnet Development Program. 52 and altered bending moments under fault conditions when one or more coils undergo a quench. All of those calculations as well as the shape of the plasma have bearings on an operating and economic comparison between circular and oval-shaped coils. If the plasma is circular, then clearly a circular coil will require less superconducting material and while it may require more structure it may be easier and hence less costly to fabricate than the non-circular coil. If the plasma is non-circular or if a divertor is included, then the conductor cost of an oval will be cheaper, but the structural costs may be greater. In addition the winding may be considerably more difficult and costly for a non-circular coil than for a circular coll. In the final analysis, if the cost comparisons are close, then oval coils will be preferred on the basis that they are subjected to lower stresses during steady state operation and thus offer a greater margin of safety than operation with circular coils. All of these statements assume that a transient, fault condition introduces no great disadvantage in safety and protection with the oval shape. The choice between superconducting and resistive windings for the ohmic heating and vertical field magnets is not clear at this time. First, the question of whether or not an iron core will be used is a significant decision. If we assume that air core or a combination of iron and air core winding is chosen, then the location of the windings is of paramount importance and most likely will be the deciding factor in determining which material will be used. If the OH and VF winding are located inside the toroidal field coils and are closely coupled to the plasma, then resistive (water-cooled copper) windings are feasible. If it is necessary for reasons such as ease in replacement and maintenance to place the OH and VF coils outside the toroidal coils, then the power required for resistive windings is probably too large, and it would be desirable to use superconducting windings. In considering the use of pulsed superconducting windings, we are tacitly assuming the rate of rise of field will not be large (large here is defined roughly as approximately 10 kG/sec). It must also be recognized that there are substantial losses with pulsed superconducting magnets, due both to eddy current losses in the high conductivity matrix (usually 53 copper) and to hysteretic losses in the superconducting material itself. The latter losses can be thought of occurring in a material having resis- tivity that is low but not absolutely zero. The penetration of magnetic flux in a superconductor is accomplished by creation of a resistive state (but not complete normal state) in the superconducting material. The losses in a pulsed superconducting magnet result in heating which leads ultimately to degradation. One way to achieve better utilization of superconducting ohmic heating windings is to initially bias them to a fully energized state and use the rapid discharge of the magnet windings for the fast initial heating of the plasma. Then the charging of the magnet in the opposite sense can proceed at a slower rate and avoid overheat- ing of the windings. Discharging cycles of superconducting magnets can always be done faster than charging cycles as the reduction of operating current because of heating is not important when the current is being re- duced. As with an iron core, this reverse bias would also either double the volt seconds available or reduce the size of the coils. The choice and shape of conductor material is not of particular importance at the present time unless the required field strength is above that of NbTi. In this event the development of multifilament Nb3Sn would have to be accelerated to permit sufficient testing in large magnets. The question of conductor stabilization, while a necessary design parameter, is also not crucial at the present time. However, a protection analysis of large prototype coils is important and could very well lead to constraints on the type of conductor one employs. The superconducting magnet development (SCMD) program is focused on the goal of designing, fabricating, and testing prototype EPR coils. In order to properly implement this work, it is necessary to know the required size (minimum horizontal bore) and field strength, the plasma shape, and any constraints such as minimum acceptable current density (which relates to the radial thickness of the windings) maximum tolerable field ripple at the plasma outer radius (which influences the number of coils and coil aspect ratio), and minimum aperture between coils which is acceptable for diagnostics and neutral beam ports (which also relates to coil aspect ratio). The SCMD program will bring out other possible constraints. For example, an analysis of the out-of-plane loads may require coils above some minimum 54 radial thickness, and this in turn would mean a larger number of coils for a system. The whole question of coil protection will have a dominant influence on an acceptable value of current density and have a bearing on the structural and cryogenic considerations. 55

3.6 Tritium * R. N. Cherdack J. S. Watson

The first step in scoping the tritium systems for an EPR is to estimate the rates of consumption and throughput. The approximate rate of consumption can be simply calculated, the only assumption required being the total energy per fusion (including reactions in blanket and shield). Assum- ing 20 MeV/fusion, the consumption rate is 0.135 g T/MW-day. Since 1 g of tritium is equivalent to 9640 curies, the consumption rate is approximately 1.30 x 103 Ci T/MW-day. The throughput rate depends upon the burn fraction that can be achieved, but is probably about one hundred times the tritium consumption rate. Thus if the EPR operates at an average thermal power of 150 MW, the tritium consumption rate will be about 20 g/day (200,000 Ci/day) and the throughput will be roughly 2 kg/day (20 MCi/day). An obvious question is whether the projected consumption of tritium in the EPR can be supplied from then-existing ERDA production channels, or if it requires that the EPR breed its own tritium supply. A reasonable expec- tation for the EPR (based upon the typical length of operation of experimental fission reactors in the completion of their missions) is about two equivalent full-power years of operation. A thermal power of 150 MW for two years would consume approximately 15 kg of tritium. Upon the basis of presently unclassified information, it can be stated that, given ample advance notification and barring unforeseen higher-priority demands, this quantity of tritium can probably be provided to the DCTR program from nor- ** mal ERDA production channels. Tritium breeding in EPR is, therefore, not expected to be an essential part of the plant operation and preliminary conceptual designs should not be constrained to provide breeding capability.

Bums & Roe, Inc. Under USAEC policy, charges to the DCTR program would be essentially shipping and handling costs; current ERDA policy is presumably the same. S'nee EPR operation is more than ten years in the future, however, this policy could change, especially if there is a relocation of research and production functions in different agencies. 56

The foregoing does not mean that there is no incentive to produce small amounts of tritium experimentally in the EPR. This will most likely be desirable in one or more of the several replaceable blanket modules. One purpose of the tritium production experiments in the EFR would be to obtain verification in integral experiments of calculational procedures and fundamental neutronic data used to predict breeding in fusion reactors. Another would be a demonstration of tritium confinement and removal techniques by small-scale operation of a system with future applicability. Whenever the time comes to select the designs of the experimental blanket modules, the goal will be to test or demonstrate the essential features of the blanket systems that at that time are the leading candidates for subsequent reactor application. Choices for the experimental modules need not be made until several years after the design choices for the basic EPR machine. For the present, therefore, EPR conceptual design should include a strong emphasis on the primary tritium system with much less effort on possible experimental blanket module tritium systems. The design of the containment systems must, of course, consider both the primary system and the experimental module systems.

3.6.1 Process Requirements for Primary Tritium System

The high throughput rate of tritium in the EPR makes recycling within the plant a practical necessity. In the design of the process equipment for this recycle, three important considerations are recovery fraction, inventory, and leakage. High efficiency tritium recovery processes will be used, but absolute recovery will be impractical. It is not possible at this time to predict accurately the highest recovery fraction that can be attained, but we can specify a reasonable reference or target value. As- suming that the burn rate is one percent of the throughput rate and that * process losses should be less than 10% of the burn rate, the recovery fraction must be at least 99.9%. Although the possibilities for even better * Process losses must be predominantly in discard or waster material rather than leakage to the secondary containment. 57 recovery should be explored, this fraction is likely to be close to the practical limit and is, therefore, an appropriate target in conceptual design studies. Logistics, economics, and safety considerations dictate that the inventory in the process system be as low as practicable. A reference value can be obtained as follows. Cryosorption pumps, if used, will have to be regenerated frequently, say daily. In this case these pumps would contain about one day's throughput, 2 kg. Assuming that the inventory in the other process equipment amounts to about the same, the total process inventory would be about 4 kg. Leakage from the process equipment (and from the entire tokamak machine, for that matter) constitutes a load on the secondary containment system and therefore must be minimized. The principal tritium handling equipment for the EPR will be essentially vacuum system components. The systems for EPR could be similar to the cryosorption systems in the ORMAK-F/BX conccptual design.3 Before any firm decision on the EPR, however, other storage type systems such as re- generable getters and other process systems such as mercury diffusion pumps should be examined. Pumping speed and hydrogen isotope storage requirements will affect these considerations. For example, 1% burn rate and daily regeneration of vacuum pumps implies a storage capacity on the vacuum pumps of 10,000 liters of hydrogen isotopes. Typical cryosorption pumps associated with this storage capacity would have a total pumping speed of 10,000,000 liters per second. If this speed is much greater than the EPR tokamak operation requires, then either special cryosorption pump designs (containing more sieve per unit volume) or lower speed mercury diffusion pumps will be considered. Even if tritium handling equipment for EPR resembles the ORNL conceptual design of equipment for ORMAK-F/BX in many ways, there will be some important differences. Most of these will result from differences in the size (tritium- deuterium throughput) of EPR and a fusion test reactor, but a few differences will reflect our more recent thinking. As noted earlier, the cycle time for pumps and other process equipment must be shorter in EPR, so advanced pump regeneration techniques will be required. Rapid, low-temperature regeneration of cryosorption pumps appear to be possible, but experiments are currently underway (at HNL) to confirm this point and evaluate proposed 58 regeneration procedures. Removal of helium from uranium beds will have to be done more efficiently in EPR to avoid losing tritium since the required percent recovery will be considerably higher. The larger quantities of gas involved could, on the other hand, make a few operations simpler in EPR. It may be possible to remove tritium-deuterium from uranium beds at higher pressures, perhaps at pressures high enough for recycle to the plasma. The possibility of a divertor for EPR has very large implications for the tritium handling vacuum systems and may require developing different conceptual designs taking into account various divertor concepts. Isotope separation capability will definitely be required at the EPR site. The throughput and separation required cannot be specified now, however, because they depend largely upon the characteristics of the systems for injection heating and fueling of the plasma, which are still undefined. The technology of hydrogen isotope separation is well established, and only a limited amount of development appears to be required for EPR. Early conceptual studies therefore need not include a great deal of effort in evaluation of alternative separations methods and their development needs. A preliminary conceptual design of an isotope separation system for EPR can be prepared on the basis of presently unclassified information. Ultimately, however, the most rational choice of the best system for actual incorporation in the EPR plant requires consideration of presently classified information on existing, tested and proven systems in ERDA production programs. Containment techniques for EPR are expected to be similar to those that wera envisioned for ORMAK-F/BX. Because the quantities of material to be contained will be much greater, even greater reliance will be placed on the containment and monitoring devices. The volume of containment atmosphere and the cost of containment will not scale linearly with the quantity of tritium involved, so costs of this type of containment equipment should still be manageable. Considerations of other details in tritium handling equipment design will be studied as decisions are made and information generated in other parts of the EPR design effort. Items of particular interest to the tritium system design are as follows. 59

1) Primary and secondary vacuum pumping speed requirements. 2) Pulse schedule. 3) Feed methods (gas fill, injector, solid fuel?) 4) Number of feed points. 5) Injector capacities and efficiencies. 6) Injection ion composition (D-T mixtures or separate injection). 7) Purity requirements for feed and injected material.

3.6.2 Radiological Aspects of Tritium Handling Systems

There are essentially two radiological hazards of the tritium handling systems. The first is the tritium leakage from the systems to their surroundings, including buildings and the general environment. The second is the hazards associated with maintenance of parts of the system in close proximity to the reactor. The control of tritium leakage for normal operating, maintenance, and emergency conditions should be the most important consideration for all tritium handling systems. This overriding consideration implies that the following criteria should probably be adopted for tritium handling systems. 1) If feasible, all tritium handling equipment shall be located in the reactor building. The reactor building should have air tightness and access control adequate so that no more than 1 percent of the building atmosphere escapes per day except as a properly monitored and processed stream from an elevated release point under both normal and emergency conditions. If tritium handling equipment is located outside the reactor building, it shall be in a building similarly leak-tight and with similar atmosphere monitoring and processing provisions and discharging from an elevated release point. 2) The contents of the tritium handling systems shall not be released as a result of credible seismic or other environmental disturbances. Safety analyses must consider effects of facilities and equipment whose failure might in turn induce failure in the tritium handling systems, e.g., power supplies, structural members, potential missiles. 3) All components and piping handling environmentally significant quantities of tritium shall be doubly enclosed. Enclosure atmospheres 60 shall be maintained at a negative pressure relative to the building atmosphere and shall be monitored and processed for tritium removal. 4) All tritium processing, where feasible, shall be done at temperatures and pressures below those which lead to significant release by diffusion through the primary containment barrier. 5) A system shall be provided to remove tritium from the reactor building atmosphere. Tritium concentration in the reactor building shall be maintained at less than 10 percent of the controlled access area MPC during periods of normal operation (personnel access permitted without special protection). Tritium content at other times shall be determined by analysis of leakage modes to the environment and by reasonable operating and maintenance requirements. 6) The reactor building shall be adequately instrumented to monitor all localities within the building which are likely sources or collection points of tritium. Appropriate alarms shall be provided to alert personnel within the building and at control points of the existence and location of excessive concentrations. 7) All anticipated routes for tritium release to the external environment shall be monitored. The problems of operating and maintaining radioactive equipment must be given careful consideration in the design of the tritium handling systems. Designs which allow remote operation and maintenance will be fa- vored. For the equipment subject to significant gamma and neutron fluxes, materials choices must consider the constraints of radiation damage and neutron activation. If equipment made of suitable materials and adaptable for radioactive maintenance it not commercially available now, development needs must be identified and scoped. The complete design must allow for normal operation and maintenance without doses to personnel exceeding a few tens of millirem per week. Neucronics and shielding calculation must be performed on the vacuum pumping systems and the tritium handling equipment in the vicinity of the reactor. All other tritium handling equipment should be located in specially shielded areas removed from the immediate vicinity. 61

3.7 Materials and Fabrication

A. J. Moorhead

There are three basic criteria for materials and fabrication techniques that apply to all EPR systems. • They must do the job. (The resulting machine must be capable of meeting project technical goals in a safe, dependable, and effective manner.) • They must be available when needed at a reasonable price (per- mitting construction on the required project schedule and within allowable costs). • Insofar as possible, they must be adaptable for more advanced reactors following the EPR. Although these criteria are so obvious that their statement might seem un- necessary, there is a need to embody them in more specific gvidelic^s that are to be used in making EPR design decisions. For example, some compro- mise decisions will likely be necessary between the last two criteria: one implies choice of well-proven, readily available materials and conservative designs; the other, solutions that are less well developed but have greater development potential. Decisions will require both the quantitative evaluation of all the factors involved and a weighting of the factors on the basis of the design guidelines. For the purposes of the EPR scoping studies of materials and fabrica- cation techniques, it is convenient to break the machine down into the following components and systems: 1. surfaces facing plasma, 2. blanket, 3. experimental blanket modules, 4. shielding, 5. superconducting coils, 6. neutral beam injectors, 7. diagnostic devices, and 8. primary tritium handling system. 62

Preliminary consideration has been given to the special requirements of the EPR in each area: here we discuss only areas 1, 2, 3, and 5. (Ma- terials and fabrication problems in all areas are being addressed broadly in the Fusion Reactor Technology Program.)

3.7.1 Surfaces Facing Plasma

The surfaces that face the plasma present some of the most critical problems in materials selection, design, and fabrication. The problems include: (1) sputtering, which can have a crucial effect on the plasma as well as eroding the exposed surface, (2) outgassing, which can also have a significant effect on the plasma, (3) radiation damage effects due to fast neutrons, which cause the material to become brittle and change dimensions, (4) energy handling (heat generation and removal), which involves high temperatures and cyclic stresses, and (5) design of subassemblies and support structures to permit remote removal and replacement after they have become intensely radioactive. Depending upon the specific design of the tokamak EPR, surfaces in several different components may be exposed to the foregoing effects. One will be the wall which constitutes the boundary between the vacuum chamber and the blanket. Most likely this will be screened, at least partially, from the plasma by a liner or curtain whose specific purpose is to inter- cept impinging particles and soft radiation most effectively. Another special surface situation will exist in the divertor (if any) where there will be intense impingement of particles, resulting in high fluxes of energy. Another possibility is physical limiters which may constitute only a small part of the surface but receive a disproportionately large fraction of the energy from the plasma. The most general statement of the first-wall question is: what material in what configuration achieves the lowest level of contamination of the plasma, sustains the least amount of damage itself, and effects the greatest amount of protection to the structural components beyond? Al- though the radiation fluences and resulting damage to the first wall will be lower in EPR than in a commercial system, a major factor in the selection of material and configuration for this wall will certainly be the potential for use in follow-on reactors. Because of the inevitable uncertainty 63 in the application of experimental data, there is a strong incentive for realistic in-service testing of candidate commercial reactor liner materials and configurations in the EPR. (Successful operation in the EPR would lend confidence to the design of a liner for the more extreme operating environment of a commercial system.) It appears that an ideal first wall would have the following characteristics: 1. a low effective sputtering yield, 2. a low atomic number, 3. high binding energy, 4. good compatibility with hydrogen, and 5. good thermal characteristics. To meet all these characteristics, a liner may have to be selected on the basis of both material and configuration considerations. Inner walls under consideration for the EPR besides a bare metal wall include graphite or carbon cloth curtains;21 metallic honeycomb or geometric patterns "scribed" on a substrate;23 and ceramic coatings such as SiC,23 ZrC, or ZrN. The ceramic coatings may be applied to either a plane surface or to various substructures such as graphite cloth or honeycomb. The concept of a graphite or carbon curtain to protect the first wall is very simple: one or more, layers of a woven cloth would be attached to the first wall by insulator pegs such that no part of the curtain physi- cally touches the wall. The practicality of such a scheme depends upon favorable answers to several questions that are presently outstanding. One is the effect of radiation on the fibers and cloth. Although data on radiation damage of graphite appear to show promise for this material as a liner, most of the reported results are for reactor-grade graphites rather than for carbon or graphite fibers. Some recent work on irradiation of annealed, massive, highly oriented, pyrolytic carbons has suggested that carbon fibers, which also have a high internal preferred orientation, are likely to shrink excessively when exposed to fluences expected for fusion reactors.2* Further work is needed in this area. Another question is outgassing. Encouraging results are being obtained in outgassing experiments being conducted by McDonnell-Douglas for the University of Wisconsin*3 and 64 other outgassing tests are now planned. Another potential problem area which must be investigated prior to specification of a graphite curtain for EPR is chemical sputtering — i.e., the reaction with D° and T° particles to form hydrocarbons such as methane. A honeycomb structure or a geometric pattern scribed on the first wall may be amenable to use in EPR, as they serve (because of their configuration) as traps to retain sputtered particles. The honeycomb being considered may be "macrohoneycomb" in the form of a cellular structure made by welding together formed pieces of metal foil, as widely used in the aerospace industry; or "microhoneycomb" made by etching a similar pattern (but on a much smaller scale) on a metal surface. Macrohoneycomb would be supported by frames and suspended from the first wall much in the same way as a graphite curtain. Microhoneycomb would be formed on the first wall by such techniques as electrochemical etching (as used to make printed-circuit boards) or possibly by laser or mechanical scribing. Hopefully if a macrohoneycomb were selected, a commercially available product such as titanium or stainless steel could be used. However, the material of construction of this honeycomb may have to be a material such as tungsten or niobium, which has low sputtering coefficients, in order to avoid contamination and degradation of the plasma by particles sputtered from the honeycomb itself. Although the technology is well developed (in the aerospace industry) for the fabrication of stainless steel or titanium honeycomb, there has been relatively little work done on the fabrication of refractory metal honeycombs. There have been small amounts of Nb 752 and TZM honeycomb core made by Martin Marietta in Baltimore26 but very special procedures were required. Titanium honeycomb specimens will be included in sputtering and outgassing studies at ORNL and their further consideration as a liner material will partially depend on the results of these tests. If the honeycomb configuration looks generally promising but it is decided that a material other than stainless steel or titanium is required, then a large development effort would have to be conducted to develop procedures for fabrica- tions of honeycomb from "nonconventional" materials. Eventually, an industrial manufacturing base would have to be established. 65

A major problem attending the selection of a material and configuration for an EPR inner wall is the development of techniques for the initial attachment of the liner to the blanket and the replacement of the liner at periodic intervals. The latter problem is compounded by the radioactivity induced in the liner and blanket, necessitating remote removal and installa- tions of liners which must be kept in mind in the selection of materials, configurations, and attachment techniques for EPR liners. Another major material selection and fabrication problem may arise in EPR if it is found that a limiter is required in the system. Limiters are necessary on small experimental machines and function as a protective shield in front of the first wall to absorb and disseminate the large amount of heat generated if the plasma brushes against the wall. It is not known whether a limiter will be required on the large machines such as EPR. Limiters have been envisioned both as shields or belts of high melting-point materials such as tungsten or as a series of SiC knobs pro- truding from the wall as in the General Atomic "porcupine" limiter. In either case, it is expected that considerable development effort would be required before building a limiter for a machine the size of EPR.

3.7.2 Blanket Structure

As presently envisioned, the EPR blanket would operate at reasonably high temperature (up to about 600°C), be subjected to some thermal cycle during each plasma pulse and a cycle to room temperature during shutdowns, be exposed to a damaging fluence of high-energy neutrons, and be required to remain quite leak-tight to prevent contamination of the plasma. At present, of the well-characterized, commercially available, readily fabricable materials, type 316 stainless steel appears to be the most likely to meet the design criteria for high-temperature blanket structure. This material has the distinct advantage of having been extensively studied for use in LMFBR's and HTGR's, so that a great deal of information on radiation effects and high-temperature mechanical property design data (creep, fatigue, etc.) are presently being obtained. An area of concern is the possibility that radiation displacement damage (3 dpa in 2 full- power years, based on a neutronic wall loading of 0.15 MW/m2) will result 66

In some matrix hardening of type 316 stainless steel in an EPR liner. More important will be the helium produced by (n,a) reactions; at the end of EPR operation, the ductility of 316 stainless steel in the inner parts of the blanket might be on the order of 1 to 3 percent. This imposes severe design problems in the accommondation of thermal cycles. It appears that 600°G is near the worst temperature for helium reduction of ductility. Recent work at ORNL27 indicates that a titanium-modified form of type 316 stainless steel may perform more satisfactorily in the radiation environment predicted for an EPR. A five-ton commercial heat of titanium- modified 316. has been fabricated, some base-metal mechanical properties tests conducted, and a few welds made on this material, but it.s charac- terization is not nearly as extensive as that of standard type J16. Before It could be adopted for the EPR, an extensive program would have to be conducted to develop high-temperature mechanical property design data for both base and weld metal, and to simultaneously study the weldability of this material. Another possible drawback in the use of type 316 (standard or modified) in the EPR blanket (indicated by some work at Atomics International28) is that it may be subject to radiation-induced precipitation of submicro- scopic "superparamagnetic particles." Further work should certainly be done in this area to verify these findings and to identify these particles. If this transformation does occur under EPR conditions, the effect would seem to be significant as the increased magnetization might cause serious perturbation of the magnetic field confining the plasma. Although there is still a degree of uncertainty about the selection of material for the blanket of EPR, many of the fabrication problems which must be faced will be similar if any of the well known commercial austenitic stainless steels or nickel-base alloys is chosen. In the event that one of the "less-standard" nickel-base alloys such as Nimonic PE-16 proposed by Princeton0 or in the more unlikely event that a refractory metal were selected, then the complexities in fabrication of such a large field- erected structure and the amount of research and development required would be greatly magnified. 67

Another material that has been suggested for use as a blanket structural material because of its unusually low neutron activation is sintered aluminum power (SAP). (Ref. 29.) The potential advantages of low activation structural material in the EPR application must be evaluated. There are serious questions regarding the practicality of SAP as blanket structure, however. Production of this material in a homogeneous form and joining, particularly by fusion welding processes, are fraught with diffi- culties. Another area of concern is the loss of ductility due to the formation of neutronically generated gas during irradiation. This phenomenon may be critical in the use of SAP in fusion reactors and work is accord- ingly under way to study this problem. One area that needs wcrk in any case is in the developuient of specialized equipment for remotely joining, inspection, and subsequent removal of blanket segments. There has been a substantial amount of development in this area at ORNL and elsewhere including demonstration of operability in radiation environments. (In high radiation fields there is some degradation of individual components, resulting in shortened lifetimes for equipment.) For welding of the final seam joining individual blanket segments, we envision a weld head, such as is used in a commercial automatic pipe welding system, that will orbit around the stationary weld joint.30 De- velopment would be required to modify this device for welding of the large diameters required in EPR, and to develop the necessary orbiting inspection and cutting modules.

3.7.3 Experimental Blanket Modules

The structural material for these modules have the same criteria as that in the standard blanket modules, with the additional requirements of compatibility with breeding materials (lithium or lithium compounds) and larger amounts of tritium. As far as lithium compatibility is concerned type 316 stainless steel (or a modified version of this alloy) appears to be a suitable material. This material or other face-centered-cubic materials also seem to be resistant to hydrogen embrittlement. One of the major problems of fusion reactors that is being studied widely (both in CTR programs and the Molten Salt Reactor Program) is the 68 permeation rates of tritium through structural materials under EPR and power reactor conditions. Previous experiments (in the MSRP) have shown that hydrogen diffusion rates are about three orders of magnitude lower in tungsten than in any other material studied. Conceivably one could coat the inside of a breeding blanket (and the tritium handling system also) with a layer of tungsten (by chemical vapor deposition, for example). However, a significant effort would be required to develop this technology adequately for EPR application. There is also evidence that coatings such

as Cr203, Al203, or Y203 have much lower hydrogen diffusivities than most other materials. With development it might be possible to form relatively impervious oxide coating on the inner wall of a breeding blanket structure and thereby greatly reduce tritium permeation.

3.7.4 Toroidal Field Magnet

The superconducting toroidal field magnet can be best examined from * a materials and fabrication viewpoint if it is considered as two separate (but closely related) subsystems: (1) the superconducting composite and windings, and (2) the magnet housing and structural support. There are two major environmental conditions to be dealt with in these magnets — the high magnetic fields generated and the cryogenic operating temperature. The Superconducting Magnet Development Program, which has as its goal the development of the toroidal field magnet system for the EPR, is concentrating primarily (not exclusively) on the ductile niobium-titanium alloys. There exists a substantial body of experience in the production of NbTi conductors and many large magnets have been successfully built using these materials. Considerable additional development will be required, however, to meet the particular requirements of toroidal reactor magnets in an op- timal manner. The advantages of aluminum as a stabilizing material have long been known, but NbTi superconductor in an aluminum matrix is not presently available. Copper-stabilized NbTi material is commercially available in a variety of shapes, however, and production of improved copper- and cupronickel-stabilized NbTi multifilament superconductors is being investigated by commercial vendors under the auspices of the SCMDP.

In actual practice some of the structural support can be incorporated in the coil winding. 69

Consequently the availability of suitable NbTi materials in time for EPR use seems assured. The critical fields for the NbTi alloys, which are around 8 tesla at 4.2K, are one of the principal factors limiting the plasma conditions that can be attained in the EPR. If experiments in PLT indicate unfavorable plasma scaling with size and temperature, there will be a very strong incentive to provide higher fields in the EPR. The confound Nb3Sn is the leading candidate superconductor for use in higher fields. NbaSn is now available commercially in the form of thin ribbons, but although magnets have been successfully built of this material, its suitability for use as the principal material in the EPR magnets is generally regarded as doubtful. Multifilament Nb3Sn superconductors are being developed under the auspices of the High-Field Superconducting Magnet Development Program at the Lawrence Livermore Laboratory for an intended application in the mirror reactor of the Fusion Engineering Research Facility, (multifilament NbaSn has also been developed in England.) Although the FERF is envisioned for construction in about the same time frame as the tokamak EPR, the specification of multifilament NbaSn for the EPR magnets would undoubtedly impact the EPR schedule because of the additional specific development that would be required. Materials such as NbgGe and other A-15 internetallic compounds with even higher fields than Nb3Sn are being investigated, but their availability in the near term is doubtful. One of the fabrication problems in superconducting windings is the joining of the superconducting material and/or the composite. Development will be required to evaluate various solder systems and techniques for joining of superconductor composites, to investigate direct joining of NbTi and to determine cryogenic, mechanical, and electrical property data for the various types of joints. For the magnet structural material, the major criteria are that it possess a high elastic modulus (^30 x 106 psi), good yield strength (MOO ksi), and ductility at 4.2°K, and be nonferromagnetic at that temperature. The requirements for fabrication (especially joining) of the structure vary widely according to the design chosen. At the present time several candidate materials are being considered, such as type 310, 21-6-9, 70 and Kromarc 58 stainless steels and iron- or nickel-base suoeralioys. Much of the needed low-temperature mechanical property and magnetic behavior data is being obtained under a program on Structural Materials for Cryogenic Applications for the Advanced Research Projects Agency.'1 This effort is concentrating primarily on materials of interest in rotating superconductor equipment. Consideration should be given to utilizing capabilities in this program to conduct tests on materials pertinent to EPR such as 21-6-9 stainless steel and soldered or welded superconductor composites. The rr.quirement for nonferroraagnetic behavior is a major concern in the selection of the material for the support structure. Unfortunately, many of the austenitic stainless steels undergo a transformation to a ferromagnetic martensitic phase when cooled to or deformed at cryogenic temperatures. This transformation results not only in undesirable magnetic performance, but also a loss in ductility and dimensional changes as well. Another ferromagnetic phase (6-ferrite) can be formed in many of these materials during welding or casting. This phase is generally desirable in weldments as it has been shown to reduce the tendency for weld hot-cracking. A very important question must be answered prior to fabrication of the superconducting magnets for an EPR or even prior to selection of a design. That is. whether a fully austenitic structure (no 6-ferrite in the welds) is required from the standpoint of magnetic effects, and if so whether a practical magnet can be fabricated from fully austenitic material without suffering weld cracking. This is a complex question as hot-cracking tendencies (and thus the need for 6-ferrite) are a function of several variables such as minor element impurities in the base-material, the welding procedure, and joint geometry and restraint.

3.7.5 Electrical Insulators

Because of the electrical nature of a fusion reactor, there will be many places in an EPR (such as the neutral beam injectors, plasma confinement system, and superconducting magnets) in which electrical insulators will be required. The environments in which the various insulators will see service vary from very high temperatures such as on the inner wall or in the blanket modules to cryogenic temperatures in the magnet systems. 71

However, in most cases there would seem to be a few general criteria to be met in their selection: good fabricability and availability, compatibility with vacuum and hydrogen, 3ow electrical conductivity, and resis- tance to radiation damage. A special criterion would exist for insulators which might be used in breeding blanket modules, in an EFR as these would also have to be compatible with the breeding sedia e.g., lithium compounds. Although there is much general data available on the properties of electrical insulators being considered for fusion reactors33 there seem to be major areas of uncertainty in the effects of irradiation on dimensional stability as well as on electrical and thermal properties of these materials and on their compatibility with the various environments expected in an EPR. Consequently these are areas in which experimental work is vitally needed and some work is being initiated in bulk radiation damage effeces in electrical insulators. 72

3.8 Environmental Considerations, Facilities, and Licensing

R. N. Cherdack~

3.5.1 E~vLronment

The EPR will impact the environment in the following ways: tritium releases, thermal discharges, disposal cf radioactive components and materials, disposal vf sanitary and chemical wastes, consumption of resources, electrical yower requix£S«mts, and land use, including electrical trans- mission lines. Tritium releases during normal operation and credible accident conditions are being considered by groups evaluating tritium process systems and contaib&ent systems. Neutron activation is part of the neutronics calculations being made for the blanket and shield design. Disposal of activated components is being considered as part of the evaluation of strategies for remote maintenance. Materials utilization and consumption must be evaluated after preliminary conceptual design choices have been made and facility requirements scoped. Land use, thermal discharges, sanitary and chemical waste discharges are not expected to present unusual problems, but these, too, must be evaluated after further conceptual do- sign.

3.8.2 Facilities

EPR facilities will consist of buildings and conventional In-house utilities and service systems such as internal electrical distribution, emergency services, HVAC, service water, etc. Building requirements will be scoped out including rough sl2e estimates, based on conceptual machine design, operating and shielding requirements, and tritium containment and other radiological considerations. In-house utility service systems will be studied to determine how they differ from existing systems in type and scale. 73

3.8.3 Licensing and Safety

With regard to licensing and safety considerations for the EPR, the existing Federal Regulations require only the filing of an environmental impact statement for government-initiated projects. However, the EPR should probably be designed from the outset in accordance with the spirit of 10 CFR 50 Appendix I, which outlines goals for lowest practicable releases, particularly since the advent of F.RDA and NRC may ultimately result in more complex licensing procedures for the EPR. The EPR should also comply with other technically relevant portions 10 CFR 50 as wall as 10 CFR 20 and 10 CFR 100 which while not strictly required legally as yet, do represent a set of minimum criteria which all nuclear power plants should be expected to meet. 74

3.9 Method of Accompli _">ment

E. H. Bryant and P. N. Haubenreich

Timely accomplishment of EPR objectives not only hinges upon favorable scientific findings, but also critically depends upon management foresight, planning, and preparations. The sheer magnitude and complexity of the project pose extraordinary management problems which are compounded by the compressed schedule implied by the 1985 target date. Cost alone is not an ir.dex of management difficulty; there are close to a dozen different finis in this country*3 who are successfully managing construction of nuclear plants in the §51)0-1000 million range expected for EPR. In contrast, the Clinch River Breeder Plant, which is in this same range, has required an exceptional management organization. The EPR project will hopefully be less complex than the LMFBR demonstration plant, but the management lessons learned there"1 should be considered in the establishment of Che EPR management plan. Due to r.hc urgency of the EPR schedule and the importance and necessity of early action on items such as funding, licensing, safety reviews and environmental considerations, development and evaluation of methods of accomplishing the EPR muse be started within the next few months. Efforts at ORNL in this area ere being directed to developing and proposing by the end of FV-1975 a method of accomplishment which will bring the currently available expertise, both in and out of the current fusion program, to bear on the EPR end develop the relationships among industry and the fusion research and development Laboratories that will be required for development of practical fusion pover. Some views are emerging at this tiwc that warrant review and discussion; however, important questions of the availability and possible extent of interested industrial participation are largely unresolved. It seems, therefore, that it way be advantageous to establish a preliminary plan and organisation with the understanding that changes will occur as the projcct evolves and positions bticot&st clearer. 75

Although the manner in which industry will participate in fusion power development has not been defined in detail, there is broad recognition of its importance. The Atomic Industrial Forum has sponsored a study "to help define the policy issues associated with such industrial participation and to identify technological areas which require priority attention."35 One conclusion was that "appropriate mechanisms need to be established to facilitate a continuing industry-government dialogue on key issues and problems affecting industrial participation. The Forum could usefully serve as one such mechanism, in cooperation with other organizations in the private sector."35 Another interested organization is the Electric Power Research Institute, which is supported by 475 com- panies representing 85 percent of the nation's generating capacity. EPRI president Chauncey Starr recently wrote of energy research and development (including fusion): "It is going to take coordinated and careful management and participation by governments, national laboratories, research organizations, universities, manufacturers, and utilities. One of the roles of the Electric Power Research Institute is to bring together these various organizations — to act as a catalyst, identifying and acting on research and development needs."36 These general commitments must be built upon, and sharpened to define specific roles in the EPR project. Initial planning for the EPR project organization involves, in es- sence, a national inventory of interests and capabilities in all sectors that are relevant to the design, development, construction, and operation of the EPR. A starting point for cur inventory is Oak Ridge — specifically the Thermonuclear Division of ORNL, which is engaged in a variety of work for DCTR, and the other resources of Union Carbide Corporation Nuclear Division. Union Carbide Corporation's Nuclear Division has operated the Atomic Energy Comaission's facilities at Oak Ridge, Tennessee and Paducah, Ken- tucky since 1953. This operation, which includes the Y-12 Plant fabrication facilities, two largo uranium enrichment facilities, and the Oak Ridge National Laboratory, employs IS to 20 thousand people, including a scientific ami technical staff of ov«r 5,000 and an engineering staff of over 1000 engineers, designers, and draftsmen. 76

Normal operation of the AEC facilities by UCCND has demanded of the scientific and engineering staffs the development, design, and construction of numerous projects and facilities. Currently, there are capital projects totaling 1.5 billion dollars in progress at Oak Ridge and Pa- ducah. In the past, projects totaling hundreds of millions of dollars have been successfully brought into being by AEC-ORO and UCCND. The major * of these have involved fabrication facilities at Y-12, gaseous diffusion plant facilities, and projects, including experimental reactors, in support of the research and development of fission reactors. On large projects, the UCCND technical and engineering staffs provide preliminary and conceptual design, design criteria, design review and approval, construction supervision, and project management in accordance with AEC Manual, Appendix 6101. Where possible, Titles I and II engineering are accomplished through a prime contract with an Architect-Engineer firm selected and designated by ERDA-ORQ. Construction may be accomplished utilising lump sum sub-contractors selected on the basis of competitive bids or a cost-plus-fixed-fee contractor under a prime contract to AEC-ORO. It could be argued that UCCND has the talent and experience to manage effectively all phases of the preparation, design, and construction of an EPR. It is not clear, however, that this approach offers the most benefit to the overall goal of fusion power by the turn of the century. Demon- stration and commercial fusion reactors must be designed, constructed, and manage t by industry and utilities. These people can benefit and must be involved in the EPR in a major role. Preferably, a reactor manufac- turer or industrial participant would become heavily involved in EPR in the early stages. Involvement of industrial participants with the -\pa- bility to design and construct an EPR would allow DCTR considerable flexi- bility in later management structuring and would insure that capability exists in industry as well as with operating contractors. Also, early involvement with the team effort will develop the necessary interaction required between DCTR, research and development contractors, and industry. At the outset, a relatively small team could be established within UCCND to assist the DCTR in the organization, planning and implementation of EPR. The major role of the team would be to plan and identify requited 77 activities leading to EPR, coordinate these activities with research, development, industry, and federal agencies, and direct the conceptual design of EPR, utilizing results and input from all parts of industry and fusion research programs. Once the scientific and technological basis exists for specification of design criteria, the EPR project will become a commitment to the government to design, procure components, construct, and operate a project on a fixed schedule and within budgeted dollars. In order to meet these commitments, project management should be separate from management of ongoing research and development programs except at the highest level. Re- quirements for EPR must dictate areas of research and development and the EPR schedule will control the effort required to supply results. The existing fusion research organizations, including ORNL, must recognize and respond to the priorities to be established by the EPR and other participants must be identified and contracted when the needs arise. 78

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