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The U.S. Advanced Fuel Cycle Initiative: Development of Separations Technologies

James J. Laidler1 and James C. Bresee2

1Argonne National Laboratory, Argonne, Illinois 60439-4837, United States 2 Office of Nuclear Energy, Science and Technology, U.S. DOE, Washington, D.C. [email protected]

Abstract - Spent from 103 operating U.S. commercial reactors is accumulating at a rate of about 2,000 metric tons per year. At this rate, the legislated capacity of the Yucca Mountain geologic repository (63,000 tons of commercial spent fuel) will be exceeded by 2015. Accordingly, the U.S. Department of Energy has instituted a new program, the Advanced Fuel Cycle Initiative, which is intended to provide the technologies necessary for the economical and environmentally sound processing of spent fuel. The goal of this technology development program is to preclude or significantly delay the need for a second geologic repository. Separations technologies are being developed that will support the processing of commercial spent fuel as well as the spent fuel arising from the operation of future advanced reactors.

INTRODUCTION eliminating the short-term heat load; and (3) separate Because of its environmental advantages and the transuranic elements (, neptunium, abundant fuel resource base, nuclear power is and ) for storage or for recycle to expected to be an important source of energy in the LWRs or future advanced reactors for fissioning, United States in the future. Projections for the thereby eliminating the long-term heat load. It is growth of nuclear power in the U.S. vary over a wide estimated that the capacity of the Yucca Mountain range, with generating capacity in 2050 predicted to repository could be increased, in terms of equivalent be between 175 and 500 GWe (compared to about tons of , by a factor of 40-60 times 100 GWe today), leading to increases in the by such processing. This would ensure the inventory of spent fuel as shown in Figure 1. The of an expanded nuclear energy supply legislated capacity of the Yucca Mountain geologic system in the United States and delay the need for a repository (63,000 tons of commercial spent fuel) second repository until well into the next century. will be reached in 2015 as the spent fuel inventory grows from the operation of the current fleet of Both advanced aqueous and pyrochemical processing commercial power reactors. Even if the actual methods are being developed under the scope of the repository capacity is increased by further Advanced Fuel Cycle Initiative. The aqueous exploration, the once-through fuel cycle would process, known as UREX+, is at an advanced stage of require at least one additional repository within three technological maturity and could conceivably be or four decades. The Advanced Fuel Cycle Initiative deployed in the 2020-2025 time period. It represents of the U.S. Department of Energy is intended to a minor but significant departure from the processes provide an alternative approach to high-level nuclear presently utilized in commercial reprocessing plants waste disposal in the future, by providing a closed in and the . The fuel cycle technology that can support the current pyrochemical processing methods are directed fleet of commercial power reactors over their lifetime principally toward the treatment of spent fuels arising as well as those reactors that are deployed in the from the operation of third- and fourth-generation future. Chemical separations technology reactor plants, and their development benefits greatly development is an important part of this program, and from the experience presently being gained in the the development effort is directed toward separations processing of spent fuel from the EBR-II fast reactor. processes that facilitate the removal of those constituents of spent fuel that contribute most to the heat load and waste volume imposed on the disposal LONG-RANGE STRATEGY of high-level waste in the repository. Processes are being developed that will (1) remove over 90% of the Projections of the long-range future of nuclear power in sufficiently pure form that it can be in the United States are complicated by the existence disposed as a low-level waste or re-enriched for of many unquantifiable variables, and range from a recycle to LWRs; (2) remove over 99% of the cesium nuclear phase-out to no growth through 2025 [1] to and strontium present in spent fuel, thereby sustained growth to 300 GWe [2] or to 500 GWe [3]

ATALANTE 2004 Nîmes, France June 21-25, 2004 1 O11-01 by 2050. Taking a moderate growth scenario for the analyses and criteria. Sufficient time is available, purpose of developing a strategy upon which to base however, to resolve those issues before it becomes technology development decisions, it is concluded necessary to commit to construction of a large spent that light water reactors and advanced light water fuel treatment plant. reactors will constitute the bulk of the U.S. nuclear generating capacity for at least another 50 years. ADVANCED AQUEOUS PROCESSING Separations for the purpose of waste management will be important until it becomes practical to recycle Aqueous reprocessing of light water reactor (LWR) separated plutonium (and perhaps neptunium and spent fuel is currently practiced in France, the United americium) as mixed oxide fuel in thermal spectrum Kingdom, and . will soon begin reactors. operation of a commercial facility, the Rokkasho Reprocessing Plant. The scale of these processing Subsequently, it may be possible to reduce the long- plants is on the order of that which would be required term heat load imposed on the repository by burning to accommodate the current rate of generation of separated transuranic elements in dedicated fast- spent LWR fuel in the United States, and the spectrum burner reactors, depending upon the technologies employed are technologically mature. availability of these systems. Finally, a transition to These factors were instrumental in the selection of Generation IV reactor systems will occur, with full advanced aqueous processing as the reference closure of the . These distinct method for development as part of the Advanced periods in the evolution of the U.S. advanced fuel Fuel Cycle Initiative. Aqueous processing also cycle strategy can be categorized as a series of affords the flexibility in process configuration phases. Phase 0 is the current once-through cycle required by the multi-phase strategy: the same plant with deployed commercial light water reactors. that is used for Phase 1 can be readily reconfigured to Phase 1 is a transitional waste management phase, in support Phases 2, 3 and possibly 4. which commercial spent fuel would be processed so as to facilitate the disposal of high-level nuclear Development of advanced aqueous processing wastes in a manner that extends the effective capacity methods for the treatment of spent LWR fuel is of the geologic repository. Phase 2 would see the proceeding on a schedule that would see the selection recycle of fissile materials in advanced light water of process flowsheets for Phases 1-3 by the end of reactors as mixed oxide fuel. Phase 3 involves the U.S. fiscal year 2008. Process development is being use of dedicated fast-spectrum burner reactors to guided by the preliminary separations criteria shown destroy the transuranic elements, especially Pu, Am in Table I. and Cm, for the purpose of reducing the long-term heat load on the repository. Phase 4 represents the Table I. Preliminary Separations Criteria for Use in transition to advanced Generation IV reactors with Process Evaluation and Selection closed fuel cycles. An illustration of this strategy is Constituent Thermal Recycle, Fast Reactor shown in Figure 2; the time frames for each phase are Fertile Fuel Recycle indefinite, as are the periods of overlap of one phase of U and All with the next. TRUs Recovery Efficiency Criteria This phased strategy is considered to be consistent Uranium 90% 90% with the realities of a transition to advanced nuclear Pu/Np 99% 99% power systems. Utilities in the U.S. are likely to Am/Cm 99.5% 99.5% place new orders for advanced LWRs in the near Cs/Sr 97% 97% term, capitalizing on the great strides made in increased operational efficiency and productivity Tc, I 95% 95% with the current fleet of commercial reactors. If there Purification Criteria are to be no new orders of any reactor type, then the Uranium 99.9%, 99.97%* 99% need for an advanced fuel cycle technology is greatly Pu/Np 99.5% 97% diminished; but even if the future nuclear Am/Cm TBD 97% generating capacity were only to remain constant at Cs/Sr <100 nCi TRU/g <100 nCi the current level of about 100 GWe through 2050, ** TRU/g ** there is still likely to be a benefit to nuclear waste *Higher purity requirement is for the option of re- management from spent fuel treatment. Repository enrichment of the uranium stream benefits, of course, are open to debate and certainly **Purification as necessary to meet 10CFR61.55 subject to changes in repository performance requirements for Class C waste

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Phase 1 Separations processing scheme appears to have significant benefit The Phase 1 strategy is based on spent fuel to repository operation. The effective increase in processing for waste management purposes. repository capacity, if LWR spent fuel were to be Therefore, the process requirements are for processed prior to waste emplacement, could be as separation of pure uranium (which could be disposed much as a factor of 60. as a low-level waste), extraction of cesium and strontium in pure form (for decay storage and The elements of the Phase 1 process flowsheet have eventual disposal as low-level waste), efficient been demonstrated at laboratory scale with actual recovery of technetium and iodine (for incorporation spent LWR fuel, using the CCD/PEG process for into durable waste forms), and recovery of cesium and strontium extraction [4]. All process transuranic elements together with lanthanide fission criteria were satisfied, in most cases exceeded by a products for repository disposal as a self-protecting wide margin. An engineering-scale demonstration is waste form. planned for the near future.

Because the TRU waste is a long-term decay heat Phase 2 Separations generator, consideration is being given to storage of Phase 2 adds the extraction of plutonium (and this material in retrievable form so that it could be perhaps neptunium and americium) for recycle to recovered before repository ventilation is terminated thermal reactors. At least 30 of the existing 103 and then further processed to recover the transuranics commercial nuclear power plants in the U.S. are for recycle as fuel for future reactors. A schematic capable of burning mixed-oxide fuel, and a transition flow diagram for Phase 1 processing is shown in period is anticipated over which time the recycle fuel Figure 3. After conventional dissolution of the spent could be qualified and incentives established for fuel in nitric acid, the clarified dissolver solution is utilities to accept such fuel. Modification of the sent to a solvent extraction process called UREX. Phase 1 separations processes to achieve the Pu/Np The UREX process uses tri-butyl phosphate (TBP) as (or Pu/Np/Am) extraction step is rather simple, with the extractant, with acetohydroxamic acid added in one possibility shown in Figure 4. Illustrated here is the scrub stage to reduce plutonium to the a co-decontamination process [5], in which the initial unextractable Pu(III) state. Uranium and technetium separation would be of (1) uranium, (2) technetium, are co-extracted, and the technetium is then stripped and (3) plutonium and neptunium. The subsequent at high acidity to yield a pure uranium stream and a extraction of Cs/Sr could be with either the pure technetium stream. The transuranics and the CCD/PEG process or an alternative such as a remaining fission products are in the UREX raffinate, calixarene-based process. Most elements of the which is then directed to the Cs/Sr extraction step. various process options have been successfully The present reference process for recovery of cesium demonstrated at laboratory scale, with the exception and strontium is the CCD/PEG process (chlorinated of the separation of Am from Cm. cobalt dicarbollide/ polyethylene glycol); the use of alternate extractants such as calixarenes is also being The minor (americium and curium, or only studied. After removal of the cesium and strontium, curium, if it is possible to recycle the americium) the raffinate is denitrated to produce a mixture of remaining in the waste stream are imagined to be transuranic oxides and fission product oxides. incorporated in temporary storage forms as is the Alternatively, as shown in Figure 3, the raffinate case in Phase 1. In this case, considerable could be processed by the TRUEX process to recover development work remains to optimize the process the transuranics together with the lanthanide fission for separation of the americium and curium from products, with the remaining fission products going fission products, especially the +3 lanthanides that to the waste stream after Cs/Sr removal. In either are difficult to separate from the +3 minor actinides. case, the transuranics and accompanying fission An extensive testing program is underway in both the products are to be encapsulated and stored in the U.S. and Europe, with the aim of developing the best repository. The nature of the storage form is yet to process for Am/Cm separation. Two-step processes be decided; it could take the form of a cermet fuel (separation of Am/Cm/lanthanides from the balance rod, utilizing part of the zircaloy cladding hull stream of the fission products, followed by separation of to provide the matrix material, for eventual retrieval Am/Cm from the lanthanides) and one-step processes and use as a fuel or target in a fast reactor. The TRU are being evaluated. The DIAMEX-SANEX process product could also be encapsulated directly as oxide, has been tested with some success in various with the proviso that further processing would be laboratories, and recent U.S. tests of the CYANEX- necessary before the fissionable material would be 301® process with spent fuel have yielded excellent recycled. Regardless of the path taken, the Phase 1 results.[4] If americium is recycled, then it will be

ATALANTE 2004 Nîmes, France June 21-25, 2004 3 O11-01 necessary to develop efficient means for separation of step would make the process applicable to oxide americium from curium. fuels, both dispersion type and inert matrix fuels.

The residual fission products from Phase 2 Development of pyrochemical processing processing would be placed in a or mineral technologies in the U.S. program has been limited to waste form for repository disposal. Because the date to work on metal alloy and nitride fuels for fast remaining fission products are comparatively benign reactors. Process concept development for the (the only heat generator being Eu-154, with a half- pyrochemical processing of coated-particle fuels is life of 8.6y), the fission product loading of this waste now underway, and work with carbide fuel will begin form can be quite high, leading to a very small soon. The conduct of extensive experimental volume of high-level waste for disposal. programs, other than that involving the conditioning of EBR-II fuel, is being deferred until the Generation IV fuel types are better defined. PYROCHEMICAL PROCESSING

Fuel systems for Generation IV reactors, with the REFERENCES possible exception of the Supercritical Water Reactor, represent a significant departure from the 1. Energy Information Agency, U.S. commercial LWR oxide fuel. Many of the fuel types Department of Energy, “U.S. Nuclear Fuel that are foreseen for these reactors are intuitively not Cycle Projections 2000-2020,” January compatible with aqueous processing of the sort 2003. discussed above, and include coated-particle fuels, inert matrix fuels (ceramic-ceramic and ceramic- 2. J. Deutch, E. Moniz et al., “The Future of metal), metal alloy fuels, mixed nitride fuels (e.g., Nuclear Power,” Massachusetts Institute of AnN/ZrN, where An is ), and carbide fuels. Technology, June 2003. Phase 4 separations processes thus must consider the application of processing technologies other than 3. ANL, INEEL, LLNL, LANL, ORNL, and aqueous. The general class of pyrochemical SNL, “Nuclear Energy: Power for the 21st processes [6] offers some distinct advantages in Century; an Action Plan”, April 2003. treating the variety of Generation IV fuels. 4. S. Aase, A. Bakel, et al., “Demonstration of Electrorefining has been used for over four years for the UREX+ Process on Irradiated Nuclear the conditioning of spent fuel from the EBR-II Fuel,” 13th Annual Separations Science and reactor. In this process, the irradiated metallic fuel is Technology Conference, Gatlinburg, TN, chopped and anodically dissolved in molten LiCl- October 2003. KCl salt. Uranium is electrotransported to a metallic cathode, and the transuranics are left in the salt 5. E. D. Collins, D. E. Benker, et al., together with the active metal fission products for “Development of the UREX+ Co- eventual incorporation in a ceramic waste form. Decontamination Solvent Extraction Noble metal fission products (including Tc) are Process,” Proceedings, GLOBAL 2003, melted together with the stainless steel cladding hulls American Nuclear Society, p. 1270, to produce a metallic waste form. The addition of a November 2003. transuranic recovery step to this process would make it applicable to the Phase 4 processing of metallic and 6. OECD-NEA Nuclear Science Committee, nitride fuels. Tests of TRU recovery methods are “Pyrochemical Separations in Nuclear currently in progress in the U.S. and elsewhere. Applications: A Status Report", in press. Addition of an electrochemical reduction head-end

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Scenarios: 3 300x10 500 GWe by 2050 300 GWe by 2050 1.5% annual growth Constant 100 GWe

200x103

100x103 Spent Fuel, metrictons

0 2000 2010 2020 2030 2040 2050 Year

Figure 1. Growth of the spent nuclear fuel inventory in the United States under various nuclear generation growth scenarios, without spent fuel processing.

Phase 0 NOTE: in all phases, • Uranium is extracted in pure form for disposal as low-level waste (eventually, for recycle) • Cesium and strontium are extracted for separate decay storage and ultimate disposal as low-level Phase 1 waste Separations for Waste Management • Technetium and iodine are recovered and placed in durable waste forms for disposal as high-level waste

Phase 2 Thermal Recycle of Pu/Np

Phase 3 TRUs to Dedicated Burners

Phase 4 Entry into Gen IV Economy

Figure 2. Multi-phase strategy for evolution of the U.S. nuclear energy system, with emphasis on the related fuel cycles.

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Uranium and LWR Spent Uranium Low-Level Technetium Fuel Waste Extraction

Hulls, Tc ( Group extraction of TRUs, Ln Storage Form TRUs) TRU Extraction Fabrication

Hulls

Cs/Sr Decay Storage Cs/Sr Extraction Temporary Storage

Low-Level Waste Form Hulls, Tc Repository Waste Fabrication

Figure 3. Schematic flow diagram for the UREX+1 process.

LLW Disposal LWR Spent U, Tc, Pu and Uranium or Fuel Np Extraction Re-enrichment

Pu, Np Pu/Np LWR/ALWR Stripping Fuel Fab. (Co-decontamination process) Am

Cs/Sr Cs/Sr Decay Hulls, Tc Extraction Storage

Hulls To Processing

Storage Form Am/Cm Am/Cm Extraction Fabrication (temporary storage)

FPs

Waste Form Repository Fabrication

Figure 4. Schematic flow diagram for the UREX+2 process.

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