TOPICAL REPORTS
Thermonuclear fusion: Progress in a multinational project under IAEA auspices
Scientific collaboration to demonstrate the technical feasibility of fusion energy moves ahead
We' e have only three options for a long-term primary fuels for deuterium-tritium fusion by David Banner energy supply: sun, breeder, fusion." With this reactors (deuterium and lithium) are so abun- and succinct statement, the German Federal dant in nature that, practically speaking, Paul Haubenreich Minister for Research and Technology, Dr deuterium-tritium fusion is an inexhaustible Heinz Riesenhuber, pointed out in 1989 the source of energy for global energy require- incentive for current worldwide co-operation in ments." fusion energy development. Two basically different approaches to peace- The status and prospects for success in the ful application of fusion energy are being development of controlled thermonuclear pursued. They are usually called "magnetic fusion were reassessed in 1990 by the Interna- confinement" and "inertial confinement". tional Fusion Research Council, an advisory (See boxes.) body to the IAEA with members from all parts Although the feasibility of international of the world. The Council's report included the exchange of information on inertial fusion is the following statement: "Against the background subject of recent interest, this line of develop- of recent experience, the need for the develop- ment has been supported mainly by the United ment of diverse and widely accessible, long- States. In contrast, research on magnetically term sources of energy is perceived more and confined fusion has long been carried out in more acutely. These energy sources should not many countries, at a total annual expenditure only be technologically feasible but also accept- approaching two billion dollars. The bulk of the able from the economic, safety, and environ- effort is in four large programmes in the mental points of view. Fusion has the potential European Community (EC), Japan, Soviet of becoming one of these sources. Union, and United States. Several other coun- "Developing a new source of energy such as tries support smaller but significant research fusion is a formidable scientific and technologi- programmes. cal challenge which spans several human gener- For more than 30 years, magnetic fusion ations. Yet the continuity in, and the magnitude research has enjoyed an extraordinary degree of, the progress achieved so far on the way to of international co-operation. From its incep- the reactor are impressive and augur well. The tion, the IAEA has actively promoted the worldwide exchange of scientific information on fusion. Since 1987, it has been actively involved in more concrete, larger-scale multi- Mr Banner is Head of the Physics Section in the IAEA's national co-operation in the International Division of Physical and Chemical Sciences and Mr Haubenreich is the former Secretary of the ITER Thermonuclear Experimental Reactor (ITER) Council. project.
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ITER project: International ings in Vienna during 1987, at which they thermonuclear experimental reactor developed a detailed description of a 3-year joint effort called International Thermonuclear By about 1986, progress in each of the four Experimental Reactor Conceptual Design major fusion programmes had reached the point Activities (CDA). The purpose was to take a that the next logical step was to build a device first concrete step toward construction of a incorporating fusion reactor technologies that machine that would meet the needs of all four would be large enough and powerful enough to programmes. The unanimously chosen techni- achieve "ignition" and "controlled burning" cal concept was the so-called "tokamak" con- of fusion fuel. It was apparent to all involved cept of magnetic confinement of plasma, which A view inside the Joint European Torus (JET) that this next step would require great had been developed originally in the USSR and tokamak, the world's resources, both of technical personnel and of subsequently, in increasing scale and sophisti- largest magnetic funds for construction and operation. In view of cation, in many countries. The Director confinement experiment. the tremendous incentive for further progress General then invited each interested Party to In this chamber, during and the scale of the next step, leaders of the co-operate in the CDA, under the auspices of experiments, hydrogen plasma is created and governments supporting fusion development the IAEA, in accordance with the Terms of magnetically confined at began calling for expansion of existing co- Reference that had been worked out. The four conditions required for operation in fusion research. Parties accepted and committed themselves to thermonuclear fusion, In response to these calls, the IAEA Director the efforts necessary to produce a conceptual including temperatures design, cost estimate, and siting requirements approaching General invited representatives of the four 100 000 000° Celsius. major fusion programmes to a series of meet- by the end of 1990.
IAEA BULLETIN, 1/1991 TOPICAL REPORTS
Joint design activities began in April 1988 it was no small accomplishment of the joint and were successfully completed in December work that understanding and resolution of these 1990. Part of the effort was in the home coun- differences were soon achieved. By the end of tries, part at a joint work site provided by the 1988, the ITER Parties had agreed on choices European Community at Garching near of machine parameters and design concepts for Munich. During joint work sessions, which magnets, materials, and maintenance arrange- lasted about 6 months each year, more than 50 ments. scientists and engineers were in residence at the The design process was supported by exten- joint site while an even greater number con- sive research and development (R&D) by the tinued to work at home. An integrated organi- Parties. Each spent about US $10 million per zation for the joint work encouraged close year on technology R&D, besides ongoing con- collaboration of scientists and engineers from finement physics experiments that included the four Parties. Overall direction of the ITER many tasks specifically undertaken for ITER. activities was provided by the ITER Council, ITER's results were analysed and adopted as with two members from each Party. part of the basis for confident design. Although the four fusion programmes had By the end of 1990 the four-party teamwork similar objectives for an experimental reactor had produced a conceptual design of an entire and were in agreement on the general technical plant and a clear picture of how ITER might be approach at the beginning of the ITER activi- built and operated. This included a description ties, there were differences among the specific of construction site requirements and a sug- design concepts that each had developed. Thus, gested project plan. The plan includes descrip-
The principal elements of the ITER tokamak: 1) toroidal field coil; 2) vacuum vessel; 3) plasma; 4) divertor; 5) central solenoid; 6) blanket and shield; 7) horizontal access port; 8) poloidal field coils; 9) vacuum pumping duct.
m
IAEA BULLETIN, 1/1991 17 TOPICAL REPORTS
COLLISION
Thermonuclear fusion DEUTERIUM (D) TRITIUM
tion of physics and technology R&D tasks, The prospective EDA Parties developed a shared among national programmes, which logical organization of the work that could would be needed to support detailed design. allow equal sharing. They estimated that about The ITER parties also developed a possible US $250 million would be spent on design schedule and a preliminary cost estimate for work and US $750 million on direct support of construction and operation. technology and engineering R&D. About half At the conclusion of the CD A, the results of the design work would take place at a joint were thoroughly reviewed, both jointly and by work site, carried out year-round by a Central panels within each of the four Parties. All Team of up to 180 scientists and engineers, reviews reached the same conclusion: that the drawn from all Parties, plus local support. results provided a good technical basis for Specified design tasks would be done in labora- proceeding with the next logical phase of the tories and industrial firms located in the home ITER project. countries of the four Parties. Programmes of The ITER team during the CDA made a physics research by ITER Parties and others preliminary estimate that construction of ITER would continue to provide information to con- would require 7 years and a capital investment firm the ITER design and to plan its experimen- of about US $4.9 billion, shared among the par- tal programme. ticipants. Before ITER construction could All of the ITER-specific technology R&D begin, about 6 years would be required for tasks would be carried out by one or more Engineering Design Activities (EDA), includ- Parties at sites within the home countries. ing detailed engineering, further development Project management would be by a Director of components, and evaluation of proposed and his staff, supported by a common fund. construction sites. Since ITER is viewed by the four Parties not
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Fusion initiation and confinement
In magnetic confinement concepts, fuel tical fusion power can be defined. The latter is that is initially in the form of rarefied, cool gas effected primarily by making the plasma cham- is heated by any of several means until it ber large and the magnetic fields strong. becomes a plasma. This "fourth state of mat- The basic principle of inertial fusion is ter" is reached when the thermal motion of the extremely rapid heating of.fusion fuel, resulting atomic particles is so vigorous that nuclei and in abundant, energy-producing fusion reac- electrons become separated. tions before the forces on the atomic and sub- Since every particle in a plasma has an atomic particles cause the reacting mass to fly electric charge, they are subject to forces apart. In the approach being considered for when traversing a magnetic field. The trick in power-station applications, a tiny pellet of magnetic confinement is to configure the mag- frozen hydrogen is dropped into a chamber netic fields so that most of the charged parti- where it is abruptly hit by a pulse of laser cles are forced to travel in curved paths that do energy, focused on the pellet from several not intersect the walls of the chamber in which directions. (See figure.) The rapid surface heat- the plasma is formed. Heating must then con- ing creates an implosive shock wave that heats tinue until the thermal motion of the particles and densifies the center of the pellet to ther- reaches the velocity range at which collisions monuclear fusion conditions. In the tiny frac- produce fusion. tion of a second before the pellet explodes, the Scientific understanding has been highly fusion energy is produced. Utilization as a developed, to the point that heating methods power source requires a continuing series of and confinement efficiencies required for prac- such events at close intervals.
Laser beams
Pellet to be injected
only as a demonstration of the technical feasi- in Vienna for these negotiations and assured bility of fusion power, but also as a demonstra- them of the Agency's readiness to provide its tion of the safety and environmental services in establishing and supporting the envi- advantages, ITER's safety and environmental sioned EDA Central Team. The first negotiat- concerns would continue to be guiding princi- ing meeting was held at the Vienna ples in the engineering design. International Centre on 11-12 February 1991. The results of the CDA produced not only Typical of the Parties' views were those of confidence among the technical communities; the US Secretary of Energy, who said with governments also were convinced of the desira- regard to the negotiations of an agreement for bility of continuing with ITER in view of the ITER's EDA: "It is fitting that, as international tremendous potential pay-off of successful research partners, we continue our co- fusion energy. Although international collabo- operation by jointly designing the reactor that ration would be complicated, the Parties recog- could demonstrate the feasibility of fusion nized that such a joint effort would offer the energy as an energy source. Science and the beneficial prospect of sharing scarce scientific taxpayers have already benefited from this and technological resources, as well as costs in shared research that has gone on literally a priority energy development area. around the world and around the clock." After preliminary discussions among the Three of the Parties offered to host the ITER Parties revealed a high degree of commo- EDA: the EC at the site of the CDA in Gar- nality on possible arrangements for co- ching, Germany; Japan at the research center in operation in EDA, governments of each Party Naka; and the United States at a university and authorized formal negotiations. The Director fusion center at San Diego. Each offered build- General of the IAEA invited the Parties to meet ings that would accommodate up to 180 scien-
IAEA BULLETIN, 1/1991 19 TOPICAL REPORTS
tists and engineers and 120 support personnel, inexhaustible amounts. The physical require- together with computer facilities that would be ments for the production and control of ther- used in the design. Communications systems monuclear fusion have been progressively would enable effective collaboration among the determined by decades of research carried out Central Team and ITER workers in the home in laboratories around the world. The process countries. that produces the energy is the same as that Decisions on the EDA site as well as a which produces all of the heat in the sun and choice of key personnel will be made during the stars. Thus, the ultimate objective in fusion negotiations. Based on early progress, the development can be described as the production Parties expect that, barring unforeseen difficul- and sustaining of a "miniature sun", whose ties, an agreement could be concluded by energy is harnessed to produce electricity. mid-1991. Furthermore, environmental and safety aspects of a fusion power industry promise to be quite acceptable by society. If, as ITER par- ticipants deem likely, the required equipment Potential of fusion energy proves to be practical to build, operate, and maintain, fusion could play a large role in sup- Fuels for thermonuclear fusion energy plying the world's energy needs after this production are widely distributed in practically century.
Safety and environmental aspects of fusion power
A fusion reactor is somewhat analogous to a gas heater: turn off the gas and the "flame" (fusion reaction) immediately goes out. There is no chance of a "runaway" reaction or widespread damage due to uncontrolled fusion reaction. The primary particles from fusion reactions are not radioactive. The inevitable absorption of fusion neutrons in structure or other material produces radioactive nuclides, but these are not mobile nor are they extremely long-lived, which makes containment and disposal less difficult. "Afterheat" due to radioactivity after shutdown of the reaction is relatively mild and easily manageable by simple, reliable systems. One component of the fusion fuel, tritium, is radioactive, so care must be taken in the design and operation of the facility to ensure its containment. Suitable measures are well defined and have been proven to be quite effective and practical. ITER conceptual design analyses indicate that this fusion reactor could meet all require- ments of existing regulations pertaining to safety and environment.
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