Study on the advancement of LWR MOX Fuel; Study on fuel concept for effective Pu utilization and reduction of spent fuel assemblies

Naganuma, Masayuki  ; Ikusawa, Yoshihisa   ; Shuji, Yoshiyuki ; Suzuki, Kiichi  ; Yamada, Yoshikazu ; Kamiya, Masayoshi 

As a study for advancing LWR MOX fuel, the fuel concept that can contribute to effective plutonium utilization (e.g. reduction of the number of plu-thermal plants required) and reduction of spent fuel subassemblies (interim storage subassemblies) by using existing reactors was investigated. Specifically, since an increase of Pu loading is effective for the above purposes, MOX fuel candidate concepts with the potential to increase Pu loading in the range of the current MOX fuel guidelines (Pu content: 13 wt%, burnup: 45 GWd/t, MOX fuel loading: 1/3) for PWRs were identified and compared in terms of "core and fuel design", "front-end", and "back-end", and the promising fuel concept was selected. Consequently, it was found that placing fuel elements with burnable poisons in the periphery (mainly in the corners) and adjusting the power peaking in the subassembly can increase the Pu content of the fuel elements in the periphery compared to the existing MOX fuel, which is effective in increasing the total Pu loading. Based on this measures, several fuel candidate concepts were devised, then each fuel specification that maintain criticality and power peaking equivalent to the existing MOX fuel were evaluated. As a result of the comparison of the characteristics of each candidate, the fuel concept in which UO-Gd fuel is loaded near the corners was conclusively selected as the most promising concept, because it can increase Pu loading by approximately 15% compared to the existing MOX fuel core and has a lower development burden. Moreover, schematic evaluations were conducted for this fuel concept using the Nuclear Material Balance Analysis Code, confirming the quantitative prospect on how much the above increase in Pu loading would actually affect the number of required plu-thermal plants and the material balance of nuclear fuel cycle.