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Energy in Transition, 1985-2010: Final Report of the Committee on Nuclear and Alternative Energy Systems
background 14C (0.7 person-rem/yr) and the total background (100 person-rem/yr), reprocessing that is now being practiced releases both 14C and tritium (as well as 85Kr, from which the dose is about the same as from tritium). Research is in progress on methods for trapping even this small amount of radioactivity,87 and since the chemistries of hydrogen and carbon are very well known, processes for trapping at least 90 percent of these effluents can almost certainly be developed. It is expected that these processes will be used ultimately, in accordance with the philosophy of ALARA (as low as reasonably achievable) used by regulatory commissions for effluents from the nuclear industry.
The technology for handling wastes from the reprocessing of spent LWR fuel is relatively well developed in both the United States and Europe. The typical waste is a nitric acid solution of fission products and actinides partially evaporated immediately after discharge from the reprocessing plant to reduce the volume to be stored and to recover nitric acid for recycle. After evaporation, the concentrated wastes—amounting to about 56 gal/ton of spent fuel—are routed to large double-walled underground storage tanks cooled by water and made of stainless steel, where they are held for up to 5 years from the time of reactor discharge.
When the waste has aged to the point that its radioactivity no longer requires strong cooling (less than 5 years after reprocessing), it can be solidified. For example, the Waste Calcination Facility at the Idaho Reprocessing Plant (which reprocesses highly enriched fuels from propulsion and research reactors) reduces the nitric acid solution to a frit (the partly fused state necessary for glass making, or for introduction into ceramics) of oxide granules by fluid-bed calcination. The French reprocessing plants at Marcoule and La Hague carry the process a step further by continuously incorporating the calcined solids into glass cylinders encased in steel cans. The radioactive solids are an integral part of the glass, which has the appearance of an opaque, smoothly glazed ceramic. It is expected that all reprocessing plants will ultimately use either glass or a metal or ceramic matrix as the vehicle for incorporating solidified high-level wastes.
If spent fuel is not reprocessed, it must be stored. To relieve utilities of the responsibility for storing increasing amounts of spent fuel in their temporary cooling ponds, the government proposed in 1977 to accept title and transfer of spent reactor fuel on payment of a one-time storage fee.88 At least for the time being, the stowaway fuel cycle will prevail, and the high-level waste process will involve early storage of discharaged spent fuel in water-filled canals at the reactor site (to provide gamma-ray shielding and a medium for heat dissipation), later encapsulation of the unprocessed assemblies in sealed containers, and delivery of canned assemblies to the government for storage. The waste forms and storage facilities will have to be designed for safe isolation over two or three decades, and for economical recovery of spent fuel.