Year
2016
Abstract
The present generation of nuclear power reactors are thermal neutron reactors that derive energy from the fission of U235, the only fissile isotope in nature. In thermal reactors, < 1 % of the natural uranium resources are only utilized. The spent nuclear fuel from these reactors contains around 3- 5 % fission products, 1 % Pu239 and its isotopes: Pu240, Pu241, Pu242 and Pu238 and 0.1 % Minor Actinides (MAs), consisting of Np, Am and Cm. The plutonium and MA isotopes are formed in the reactor by a series of neutron capture reactions with U235 and U238, the natural isotopes of uranium fuel, followed by ß- and a decays. Plutonium is the best fuel for FBRs and U238- Pu239 is the most efficient fuel cycle in fast neutron spectrum. The MA and plutonium isotopes are fissionable by fast neutrons. More Pu239 fuel is bred in the mixed U238-Pu239 fast reactor core and in the blanket of depleted U238 than the Pu239 that is consumed as fuel in the core. Pu239 has dual use: as nuclear fuel for civilian application and as nuclear weapon material. The plutonium bred in the depleted uranium blanket, in particular, is very rich in Pu239 content. In order to ensure that clandestine diversion of plutonium for weapon purpose becomes practically impossible, it is essential to have intrinsic proliferation resistance in U238-Pu239 fuel cycle. Amongst the plutonium isotopes, Pu238 has intrinsic proliferation resistant features because of its high decay heat and the emission of significant quantities of spontaneous neutrons. The same is partly true for Pu240 and Pu242 isotopes. The MAs (Np237 and Cm 242) are the precursors of Pu238. There is a need to separate the MAs from the spent nuclear fuel and recycle in FBRs in order to ensure intrinsic proliferation resistance. Small quantities (~ 1 %) of MAs could be admixed to the U238- Pu239 fuel core and U238 blanket in order to have significant quantities of Pu238, in the bred plutonium, which will make it proliferation resistant.