nuclear fuel cycle(redirected from Discharged fuel elements)
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nuclear fuel cycle[′nü·klē·ər ¦fyül ‚sī·kəl]
Nuclear fuel cycle
The nuclear fuel cycle typically involves the following steps: (1) finding and mining the uranium ore; (2) refining the uranium from other elements; (3) enriching the uranium-235 content to 3–5%; (4) fabricating fuel elements; (5) interim storage and cooling of spent fuel; (6) reprocessing of spent fuel to recover uranium and plutonium (optional); (7) fabricating recycle fuel for added energy production (optional); (8) cooling of spent fuel or reprocessing waste, and its eventual transport to a repository for disposal in secure long-term storage. See Nuclear fuels
Steps 6 and 7 are used in Britain, France, India, Japan, and Russia. They are no longer used in the United States, which by federal policy has been restricted to a “once through” fuel cycle, meaning without recycle. Belgium, China, France, Germany, Japan, and Russia, with large and growing nuclear power capacities, use recycled plutonium. Disposal of highly enriched uranium from nuclear weapons is beginning to be undertaken by blending with natural or depleted uranium to make the 3–5% low-enrichment fuel. Similarly, MOX (mixed oxides) fuel capability can be used to dispose of plutonium stockpiled for nuclear weapons. This option is being planned in Europe and Russia, and is beginning to be considered in the United States.
Nuclear reactors produce energy using fuel made of uranium slightly enriched in the isotope 235U. The basic raw material is natural uranium that contains 0.71% 235U (the only naturally occurring isotope that can sustain a chain reaction). The other isotopes of natural uranium consist of 238U, part of which converts to plutonium-239, during reactor operation. The isotope 239Pu also sustains fission, typically contributing about one-third of the energy produced per fuel cycle. See Nuclear reactor
Various issues revolve around the type of nuclear fuel cycle chosen. For instance, the question is still being argued whether “burning” weapons materials in recycle reactors is more or less subject to diversion (that is, falling into unauthorized hands) than storing and burying these materials. Another issue involves the composition of radioactive wastes and its impact on repository design. The nuclear fuel cycles that include reprocessing make it possible to separate out the most troublesome long-lived radioactive fission products and the minor actinide elements that continue to produce heat for centuries. The remaining waste decays to radiation levels comparable to natural ore bodies in about 1000 years. The shorter time for the resulting wastes to decay away simplifies the design, management, and costs of the repository.