Physical and economical aspects of Pu multiple recycling on the basis of REMIX reprocessing technology in thermal reactors

The basic strategy of Russian nuclear energy is propagation of a closed fuel cycle on the basis of fast breeder and thermal reactors, as well as the solution of the spent nuclear fuel accumulation and resource problems. The 3 variants of multiple Pu and U recycling in Russian pressurized water reactor concept reactors on the basis of Regenerated Mixture of U, Pu oxides (REMIX) reprocessing technology are considered in this work. The REMIX fuel is fabricated from an un-separated mixture of uranium and plutonium obtained during spent fuel reprocessing with further makeup by enriched natural U or reactor grade Pu. This makes it possible to recycle several times the total amount of Pu obtained from the spent fuel. The main difference in Pu recycling is the concept of 100% or partial fuel loading of the core. The third variant is heterogeneous composition of enriched uranium and uranium-plutonium mixed oxide fuel pins in one fuel assembly. It should be noted that all fuel assemblies with Pu require the involvement of expensive technologies during manufacturing. These 3 variants of the full core loadings can be balanced on zero Pu accumulation in the cycle. The various physical and economical aspects of Pu and U multiple recycling in selected variants are presented in the given work. The better results in natural uranium savings can be achieved for the standard REMIX(UOX) approach. The usage of regenerated materials in thermal power reactors gives not more than 30% saving of natural uranium consumption. It is important to note that the use of REMIX technology in the closed fuel cycle is more expensive than the open fuel cycle with direct spent fuel disposal. It is also important to see that uranium multiple recycling in the REMIX fuel form or using the re-enrichment process leads to the degradation of the uranium isotope composition. The ²³⁶U and ²³²U concentrations in the fuel are increasing and the regenerated uranium treatment becomes more complicated