reactor, the uranium in the fresh fuel feed does not require any enrichment. At the same time, very high burnup levels can be achieved through the core arrangements with dedicated regions where Pu can be effectively bred and the regions where Pu generated in former region can be effectively fissioned [Ficher G.J. et al., 1979]. However, B&B concept employs fast spectrum to provide effective breeding of Pu. As a result, Pu in the spent fuel is rich in Pu239 isotope (over 80% of total Pu [Yarsky P., 2003]) which raises significant proliferation concerns. As discussed above, selected issues of the once through fuel cycle can be addressed via extended fuel burnup. However, the extent of these benefits is limited by the fuel performance with respect to its ability to withstand radiation damage and exposure to severe reactor operating conditions for long periods of time. Alternative fuel designs such as coated TRISO particles suggested for use in advanced gas cooled reactors (Pebble Bed Modular Reactor – PBMR [Koster A. et al., 2003] and Gas Turbine-Modular Helium Reactor - GT-MHR [LaBar M. P., 2002]) can maximize the benefits of the high burnup in the once through fuel cycle.
Partitioning of the spent nuclear fuel Recycling of the SNF is the ultimate approach to diminishing the concerns over the nuclear waste in the once through fuel cycle to a considerable extent. Even after irradiation, the major part of the fuel is uranium (Figure 1.2.1). Uranium is practically non radioactive and if separated from the rest of the irradiated fuel constituents with adequate efficiency can be stored as a low level waste (LLW) or reintroduced into the fuel cycle. This would allow a major reduction in volume of the SNF and enhance the effective storage capacity of geological repository. Pu constitutes about 1% of the SNF. It can be used as fuel virtually in any type of reactor. Recycling plutonium in LWRs is a common practice in Europe, Russia, and Japan. Other countries also consider Pu recovery and develop SNF reprocessing technologies and infrastructure for that purpose. Typically, recovered Pu is mixed with depleted or natural uranium in UO2-PuO2 mixed oxide (MOX) form. Currently, the spent MOX fuel assemblies are not reprocessed. Nevertheless, even single path Pu recycling results in significant improvement in natural uranium utilization and proliferation resistance characteristics [Pellaud B., 2002].
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