MOX fuel
Reprocessing the plutonium into usable fuel increases the energy derived from the original uranium by some 12%, and if the uranium-235 is also recycled by re-enrichment, this becomes about 20%.
The System 80 reactor design deployed at the U.S. Palo Verde Nuclear Generating Station near Phoenix, Arizona was designed for 100% MOX core compatibility, but so far has always operated on fresh low enriched uranium.
[7] According to Atomic Energy of Canada Limited (AECL), CANDU reactors could use 100% MOX cores without physical modification.
Regular reprocessing of biphasic spent MOX is difficult because of the low solubility of PuO2 in nitric acid.
[11] Reprocessing of commercial nuclear fuel to make MOX is performed in France and to a lesser extent in Russia, India and Japan.
Reprocessing of spent commercial-reactor nuclear fuel is not permitted in the United States due to nonproliferation considerations.
[12] The United States was building a MOX fuel plant at the Savannah River Site in South Carolina.
Although the Tennessee Valley Authority (TVA) and Duke Energy expressed interest in using MOX reactor fuel from the conversion of weapons-grade plutonium,[13] TVA (the most likely customer) said in April 2011 that it would delay a decision until it could see how MOX fuel performed in the nuclear accident at Fukushima Daiichi.
[15] Most modern thermal reactors using high burn up uranium oxide fuel produce a significant proportion of their output towards the end of core life from fission of plutonium produced by neutron capture in uranium 238 earlier in the life of the core, so adding some plutonium oxide to the fuel at manufacture is not in principle a very radical step.
About 30 thermal reactors in Europe (Belgium, the Netherlands, Switzerland, Germany and France) are using MOX[16] and an additional 20 have been licensed to do so.
In France, EDF aims to have all its 900 MWe series of reactors running with at least one-third MOX.
This leads to buildup of heavier actinides and lowers the number of thermal neutrons available to continue the chain reaction.
The first step is separating the plutonium from the remaining uranium (about 96% of the spent fuel) and the fission products with other wastes (together about 3%) using the PUREX process.
Because americium-241 is a gamma ray emitter,[citation needed] its presence is a potential occupational health hazard.
Even under the worst conditions, the americium/plutonium mixture is less radioactive than a spent-fuel dissolution liquor, so it should be relatively straightforward to recover the plutonium by PUREX or another aqueous reprocessing method.
A subcritical reactor such as the Accelerator Driven System could "burn" such fuels if the problems associated with their handling and transportation are solved.
