Nuclear Science and Engineering / Volume 151 / Number 1 / September 2005 / Pages 25-45
If it becomes necessary to stabilize the Pu inventory before the advent of Gen IV fast reactors, then it must be multirecycled in thermal neutron reactors like pressurized water reactors (PWRs). However, because of the neutron physics characteristics of Pu, it is difficult to multirecycle it in mixed-oxide (MOX)-fueled PWRs. Indeed, since there are fewer and fewer fissile isotopes in Pu, it is necessary to compensate by increasing its content, causing it to quickly reach values where the void coefficient is positive (above 12% Pu). To avoid this, Pu must be used together with enriched U so that its degradation is compensated by an increase of 235U enrichment. Two possibilities of mixing Pu and enriched U in the same assembly are presented (homogeneously and heterogeneously). In the first, called MOX-UE, all the fuel rods are made of PuO2-UenrichedO2, whereas the second, called CORAIL, contains approximately one-third of standard MOX rods (PuO2-UtailO2) and two-thirds of UO2 rods. A variant of the CORAIL concept in which the MOX rods are substituted with inert matrix fuel rods (PuO2-CeO2) was also studied. These assemblies allow Pu to be multirecycled in standard PWRs, thus stabilizing the Pu inventory between 200 and 400 t heavy metal (for a nuclear electricity production of 400 TWh(electric)/yr, i.e., typical of a country such as France). The number of reactors loaded with Pu depends on the performances of each concept in terms of Pu burning, and it represents between 80% (CORAIL with the MOX rods) and 30% (MOX-UE with 12% Pu) of the total power. There is only a small difference regarding the needs in natural U between the Pu monorecycling option and the different Pu multirecycling options. Hence, it appears that saving U should not be offered as an incentive for multirecycling Pu in PWRs.