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Review of Doe’s Nuclear Energy Research and Development Program
FIGURE A-1 50 GWd/MTIHM spent PWR fuel actinide and fission product decay heat. GWd, gigawatt days of thermal energy production; MTIHM, metric tonnes initial heavy metal; PWR, pressurized water reactor. SOURCE: R.A. Wigeland, T.H. Bauer, T.H. Fanning, and E.E. Morris. 2004. Spent Nuclear Fuel Separations and Transmutation Criteria for Benefit to a Geologic Repository. Paper presented at Waste Management 2004 Conference, February 29-March 4, 2004, Tucson, Ariz.
are driven by the need to separate the various radioactive spent fuel constituents into separate streams to allow different solutions for each. Aside from the radioactive cesium and strontium, the main ones are the plutonium and minor actinides neptunium, americium, and curium (shown in blue in Figure A-1), which are destined for transuranic fast reactor fuel. The longer-lived fission products, technetium-99 and iodine-129, are to be sent to a geologic repository. There are also assorted other radioactive products, including gases such as tritium and krypton; uranium, which DOE wants to send to a low-level waste repository; the cladding hulls, which are destined for a geologic repository; and other wastes from the reprocessing process.
Even if GNEP worked as planned it would likely exacerbate the nuclear waste problem, at least for a long time. The most important thing to remember is that the hottest fission products would accumulate on the surface for hundreds of years. These fission products are the reason that the NRC, the last time it looked at separation and closed fuel cycles, in 1996, recommended the need for geologic repositories. Putting less of the waste into a repository is a choice we could make now without GNEP—we could leave the spent fuel in surface dry storage and put nothing in a repository. Or we may be able to site other repositories. GNEP’s notion that siting reprocessing plants and fast reactors and surface storage for radioactive cesium and strontium would be easier is fanciful.
The need for specialized fast reactors comes from GNEP’s decision to burn the plutonium and minor actinides to further reduce the repository heat load and long-lived radioactive isotopes. The main heat source after cesium and strontium’s radioactivity subsides is americium-241. A new type of fast reactor would have to be designed to burn actinide fuel (and, secondarily, to produce electricity). To make the scheme work would take about one fast reactor for every four ordinary LWRs, so about 100 fast reactors out of a total of, say, 500 nuclear units. DOE acknowledges fast reactors would be more expensive than LWRs; but in our opinion DOE still underestimates the difference in capital and fuel costs.
Further, as pointed out in Chapter 4, it would take many cycles through the fast reactors to burn up a large fraction of the actinides. That means, in effect, the spent actinide fuel from the fast reactors would be reprocessed many times (each time separating the hot fission products for surface storage). The fast reactors’ spent fuel would need an entirely new and different reprocessing technology. Each cycle—residence in the fast reactor, cooling, reprocessing, and fuel fabrication—would take a good many years. So in the best of circumstances, many cycles would take the better part of a century. But no one has yet fabricated such an actinide fuel, or designed a reactor to burn it, or developed a reprocessing scheme that could handle it. It is premature to be thinking of going beyond the laboratory with reprocessing and fast reactor technologies.
Finally, the GNEP concept applies only if there is a multifold expansion of nuclear capacity. However, even today’s optimistic projections involve a relatively small number of reactors (as of July 2007 no new reactors had been ordered);