ARTICLES (3)
Should the U.S. Reprocess Spent Nuclear Fuel?
Robert Vandenbosch and Susanne E. Vandenbosch
The U.S. administration as part of its Fiscal Year 2007 budget submission has put forward a proposal to abandon the plan to dispose of untreated spent fuel directly in a geological repository and initiate a closed fuel cycle involving reprocessing and burnup in fast reactors. This proposal is part of an initiative called the Global Nuclear Energy Partnership, GNEP[1]. In this article we will discuss the considerations involved in deciding between direct burial and reprocessing, and the timeliness of this particular proposal.
We first outline the proposal as put forward by the Department of Energy. We will concentrate on the part of this proposal dealing with the fuel cycle for U.S. nuclear reactors. The initiative also has other components, including making fuel available to other countries and returning spent fuel from these countries.
The proposed fuel cycle starts with the reprocessing of spent fuel using an aqueous approach being developed at the Argonne National Laboratory called UREX+ (for uranium extraction). Although there are a number of variants of UREX+ [2], [3] , the particular one being considered would lead to three product streams; a uranium stream comprised of much of the mass of spent fuel, a transuranic stream comprised of plutonium and other transuranic elements, and a fission product stream.[4] The uranium would be stored for eventual enrichment or as fuel for future fast reactors. The transuranic stream would be “burned” in a fast reactor. A fast reactor (with neutrons having an energy of the order of an MeV rather than of the order of eV as in conventional thermal power reactors) is required to fission Np-237 and several other transuranic elements as they have fission thresholds that exceed the energy obtained from capturing thermal neutrons. The spent fuel from the fast reactors that are used to burn up much of the transuranic elements would be reprocessed using pyrochemical techniques. (An aqueous scheme such as UREX is less suitable for the chemical form of fast reactor fuel elements.) The fission products would be disposed of in a geological repository. The UREX + reprocessing scheme differs from the PUREX reprocessing scheme in that Pu is never isolated in the UREX + scheme as it is in the PUREX scheme. PUREX was originally developed for production of Pu for weapons, and is presently used by countries such as France and Britain in their reprocessing of spent fuel from civilian power reactors.
It is not clear from the presently available information on the GNEP initiative what the plans are with respect to the present inventory of spent fuel and Yucca Mountain. The Department of Energy says it remains committed to Yucca Mountain, and that it will be needed whether or not the U.S. decides to adopt a closed fuel cycle with reprocessing. At a briefing on GNEP Deputy Secretary of Energy Clay Sell said “Getting Yucca Mountain licensed, getting it opened and getting spent fuel moved is critical, we think, to the nuclear renaissance which we are on the cusp of in this country”.[5] During testimony before the Energy Subcommittee of the Senate Appropriations Committee, Sell responded to a question from Senator Domenici saying that “we believe that up to 90 percent of commercial spent fuel could be recycled before going to Yucca Mountain”. [6] In furtherance of the Yucca Mountain project the Department has proposed legislation that would withdraw land from other uses and ease the regulatory hurdles the project faces.[7] It now anticipates a construction license application to the Nuclear Regulatory Commission in 2008.
We turn now to a discussion of the possible considerations involved in putting forth a closed fuel cycle at this time. We can roughly divide these into five categories, although there is overlap between them. The considerations that have been discussed or implicitly considered are economic savings, nuclear waste disposal simplification, proliferation resistance, public acceptance, and extending uranium fuel resources.
With regard to an economic comparison between a fuel cycle with reprocessing to that of direct burial of spent fuel, all independent studies have concluded that reprocessing is not competitive taking into account present and likely future uranium prices.[8], [9] A recent study of costs in Japan concluded that, integrated over the next 60 years, reprocessing would be about 50% more expensive than direct disposal of waste.[10] (In Japan nuclear power generators are charged about 0.2 cents per kWh to defray waste handling costs). There is one U.S. DOE analysis summary of several years ago suggesting that reprocessing would be less expensive[11].
With regard to nuclear waste disposal simplification, the situation is more complex. It is sometimes stated that there is almost a factor of 100 reduction in the amount of waste to dispose of if one reprocesses.[12] This is based on the fact that spent fuel is mostly uranium-238 that was not consumed in the reactor. This neglects the fact that the difficulty of disposing of nuclear waste involves both the heat liberated by the radioactive decay of the waste and the radio-toxicity of the waste. These latter two factors play a more important role in repository design and performance than does the volume of the waste. Both the heat liberated and the radioactivity of spent fuel is dominated by fission product decay during the first 100 years or so. Reprocessing does not ameliorate this problem. More serious analysis of the waste disposal problem suggests that the reduction in repository space required to dispose of nuclear waste is more like a factor of 10 than of 100 if reprocessing is employed. The handling of the waste is more complicated with reprocessing which involves many steps. Also the aqueous UREX + procedure generates liquid waste that has to be vitrified before being placed in a repository.
There are no proliferation advantages for reprocessing compared to direct disposal of spent fuel. Any separation of the different elements of the waste makes the fraction containing the plutonium less complex and simpler to work with. Similarly reprocessing makes the highly radioactive components of spent fuel that might be used to make a dirty bomb more accessible to terrorists. It is true that the UREX+ procedure makes the plutonium less accessible than the PUREX procedure used in earlier US weapons production and presently in Britain and France , but that is irrelevant if one is comparing the proposed reprocessing scheme with the present US direct disposal plan.
An underlying assumption in the GNEP proposal is that the public will accept the siting of reprocessing facilities.[13] It has been mentioned in presentations of the GNEP proposal that reprocessing could delay the need to search for a second geological repository site for a century. It seems to us that public resistance to accepting a nearby reprocessing plant will be as large as for a geological repository. The U.S. record on cleaning up both military and civilian spent fuel reprocessing facilities is not good. All of the high-level waste produced by reprocessing at the Hanford, WA plutonium production site is still being stored as liquid waste in tanks. A plant for vitrification of the waste is only now being built, and is still being designed as construction is in progress. The estimated cost is continuing to escalate. Similar problems are being encountered in the attempt to clean up reprocessing waste at the Savannah River Site in South Carolina. [14] The West Valley, NY facility was built to reprocess civilian spent fuel, but ceased operation in the 1970’s. It is still not fully cleaned up, and the State of New York is suing the Department of Energy in an attempt to get the cleanup completed.
The final motivation for reprocessing is to extend the uranium fuel supply. This is the only motivation that has a valid underpinning. Unless human society makes drastic changes in its demand for energy, fossil fuel supplies such as gas and oil will become quite limited within a few centuries. Although renewable sources such as wind, solar cell, and geothermal can contribute, none of these sources can provide energy on the scale of that derived from fossil fuels. While uranium is reasonably abundant on the earth’s crust, at some point as higher-grade ore is used up the cost and the energy required to extract the uranium becomes prohibitive if only the U-235 component is used. Fast breeder reactors with reprocessing can exploit the U-238 component comprising more than 99% of natural uranium.
This brings us to our final topic, the timeliness of the reprocessing proposal. The Department of Energy proposes studying reprocessing, particularly the aqueous UREX+ scheme, for two years and then deciding on whether to proceed with a pilot-plant demonstration of the scheme. This seems to us an unrealistically short time to sufficiently study the reproducibility, separation efficiency and waste stream purity of any new procedure. Pyrochemical processing is even more in its infancy, and decades of research and development will probably be needed to determine its viability and cost. Finally, there is a lot of work to be done on developing reliable fast reactors to burn the transuranic fraction from the first reprocessing step. There is no point in doing this first reprocessing step if one cannot burn the transuranics in a fast reactor. There are presently no fast reactors operating in the US . In France the most ambitious attempt, Super-Phenix, was terminated due to operational difficulties. Similarly a fast reactor built in Monju, Japan , has been shut down for decades due to an accident. (This reactor may however be restarted in the near future.)
We conclude that it would be very unwise to make a decision soon on whether to switch from a once-through fuel cycle with direct disposal of spent fuel to a closed cycle involving reprocessing and fast reactor burnup. This view has also recently been expressed[15] by Ernest Moniz, a former Department of Energy undersecretary. Considerably more research and development needs to be done. This should be done in an open and transparent manner, with significant independent peer review. The recent decision[16] of Secretary of Energy Bodman to dismiss his department’s top science advisory board is a step in the wrong direction. We also think it would be a mistake to let an over-emphasis on reprocessing divert attention and funding from completion of a geological repository. The public needs to be assured that there is a safe, permanent solution to the nuclear waste disposal problem.
Robert Vandenbosch is Prof. Emeritus of Chemistry at the University of Washington. He has served as Director of the Nuclear Physics Laboratory at this University. He is a coauthor (with John R. Huizenga) of the book “Nuclear Fission”. Prior to joining the University of Washington he was a nuclear chemist at The Argonne National Laboratory and a Fulbright Scholar at the Niels Bohr Institute.
Bobvanden@aol.com
Susanne E. Vandenbosch has a background in both nuclear chemistry and political science. She has nuclear chemistry publications based on her work both at The Argonne National Laboratory and at the Niels Bohr Institute. She has also published articles in Political Science journals. She is a coauthor with Robert Vandenbosch of a book in preparation entitled “Political and Scientific Controversies over Nuclear Waste Disposal”.
