Nuclear Fuels Reprocessing
Nuclear fuels reprocessing
Nuclear fuels are reprocessed for military or civilian purposes. In military applications, reprocessing is applied to extract fissile plutonium from fuels that are designed and operated to optimize production of this element. In civilian applications, reprocessing is used to recover valuable uranium and transuranic elements that remain in fuels discharged from electricity-generating nuclear power plants, for subsequent recycle in freshly constituted nuclear fuel. This military-civilian duality has made the development and application of reprocessing technology a sensitive issue worldwide and necessitates stringent international controls on reprocessing operations. It has also stimulated development of alternative processes to produce less plutonium and more uranium (or transuranic elements), so that the proliferation of nuclear weapons is held in check. See Nuclear power
Nuclear fuel is removed from civilian power reactors due to chemical, physical, and nuclear changes that make it increasingly less efficient for heat generation as its cumulative residence time in the reactor core increases. The fissionable material in the fuel is not depleted; however, the buildup of fission product isotopes (with strong neutron-absorbing properties) tends to decrease the nuclear reactivity of the fuel. See Nuclear fuels, Nuclear reactor
A typical composition of civilian reactor spent fuel at discharge is 96% uranium, 3% fission products, and 1% transuranic elements (generally as oxides, because most commercial nuclear fuel is in the form of uranium oxide). The annual spent fuel output from a 1.2-gigawatt electric power station totals approximately 33 tons (30 metric tons) of heavy-metal content. This spent fuel can be discarded as waste or reprocessed to recover the uranium and plutonium that it contains (for recycle in fresh fuel elements). The governments of France, the United Kingdom, Russia, and China actively support reprocessing as a means for the management of highly radioactive spent fuel and as a source of fissile material for future nuclear fuel supply. The United States forbids the reprocessing of civilian reactor fuel for plutonium recovery and is the only one of the five declared nuclear weapons states with complete fuel recycling capabilities that actively opposes commercial fuel reprocessing.
Decisions to reprocess are not made on economic grounds only, making it difficult to evaluate the economic viability of reprocessing in various scenarios. In the ideal case, a number of factors must be considered, including: (1) cost of uranium/U3O8; (2) cost of enrichment; (3) cost of fuel fabrication; (4) cost of reprocessing; (5) waste disposal cost; and (6) fissile content of spent fuel.
The once-through fuel cycle (that is, direct disposal/no reprocessing) is favored when fuel costs and waste disposal costs are low and reprocessing costs are high. However, technological advancements and escalating waste disposal costs can swing the balance in favor of reprocessing. See Nuclear fuel cycle, Radioactive waste management
The technology of reprocessing nuclear fuel was created as a result of the Manhattan Project during World War II, with the purpose of plutonium production. Early reprocessing methods were refined over the years, leading to a solvent extraction process known as PUREX (plutonium uranium extraction). The PUREX process is an aqueous method that has been implemented by several countries and remains in operation on a commercial basis. A nonaqueous reprocessing method known as pyroprocessing was developed in the 1990s as an alternative to PUREX. It has not been deployed commercially, but promises greatly decreased costs and reduced waste volumes, with practically no secondary wastes or low-level wastes being generated. It also has the important attribute of an inability to separate pure plutonium from irradiated nuclear fuel. See Solvent extraction
Both the PUREX process and the pyroprocess can be used in a waste management role in support of a once-through nuclear fuel cycle if the economics of this application are favorable. The PUREX process can be operated with a low decontamination factor for plutonium. The pyroprocess can place the transuranic elements in the salt waste stream that leads to a glass-ceramic waste form. Both systems are effective in placing the fission products and actinide elements present in spent nuclear fuel into more durable waste forms that can be safely disposed in a high-level waste repository.
Nuclear Fuels Reprocessing
the radiochemical and chemical-metallurgical processes that are used to purify spent nuclear fuel by removing radioactive fission products, to extract unused fuel material, such as uranium, and to recover newly produced nuclear fuel, such as plutonium. The separated uranium can be sent to an enrichment plant in order to increase its content of the fissionable isotope “235U. Radioactive fission products that have been separated during nuclear fuels reprocessing and are contained in a mixture with spent chemical reagents are sent to special storage facilities after they have been appropriately processed by such methods as evaporation and solidification. Long-lived isotopes, such as 90Sr and l37Cs, which are used as sources of beta and gamma rays, can be extracted from fission products.
Prior to its reprocessing, nuclear fuel is stored for a certain period to reduce its radioactivity, which is caused by short-lived fission products. Storage reduces the consumption of the chemical reagents that are used in nuclear fuels reprocessing, since the reagents generally decay upon exposure to radioactive radiation. Nuclear fuels reprocessing is automated and operated under remote control.
REFERENCEBenedict, M., and T. Pigford. Khimicheskaia tekhnologiia iadernykh materialov. Moscow, 1960. (Translated from English.)
S. A. SKVORTSOV