HKNIC - Spent Fuel Reprocessing and Direct Disposal

Spent Fuel Reprocessing and Direct Disposal
Spent Fuel Reprocessing and Direct Disposal

Spent nuclear fuel contains about 95% uranium 238 (U-238), 1% plutonium 239 (Pu-239), a fraction of a percent of uranium 235, 4% of highly radioactive fission products and a small quantity of other highly radioactive products. U-238 and Pu-239 contain a significant amount of energy and can be exploited for further use.

The quantity of high level waste or HLW arising from the reprocessing of spent fuel from a 1,000 MW nuclear power generating unit is about 1.3 tonnes a year. This waste is produced through reprocessing, which separates the useful constituents in the spent fuel – U-238 and Pu-239 – from those without any current use, the fission products and long life transmutation products. The HLW category covers about 4% of the total quantity of spent fuel.

Reprocessing is based on a chemical separation process which enables the uranium and plutonium to be recycled into fresh fuel, and reduces considerably the quantity of material that needs to be disposed at the end of the nuclear fuel cycle.

The uranium from reprocessing can be reused as the base material for fuel after undergoing conversion and enrichment. It can also be converted in a fast-neutron reactor into useable “fissile” material. The plutonium can be directly made into an oxide to be mixed with uranium oxide, creating a mixed oxide fuel or MOX that can act as a substitute for U-235 and can be used in a conventional nuclear power reactor. Alternatively, the plutonium can be used on its own as a fuel in a fast-neutron reactor.

An alternative to reprocessing is direct disposal. This requires the packaging of spent fuel, typically several decades after it has been removed from the reactor after a period of cooling, and isolation underground for several thousand years so that radioactivity will fall with time to ambient levels.