Irradiation performance of fast reactor MOX fuel assemblies irradiated to high burnups

高燃焼度照射した高速炉MOX燃料集合体の照射挙動

上羽 智之 ; 伊藤 昌弘*; 水野 朋保

Uwaba, Tomoyuki; Ito, Masahiro*; Mizuno, Tomoyasu

Mixed oxide fuel assemblies (MFA-1 and MFA-2 assemblies) were used in irradiation tests conducted in the Fast Flux Test Facility to demonstrate the capability of fast reactor core fuels to attain high burnups and fast neutron fluences. The MFA-1 and MFA-2 assemblies achieved respective peak pellet burnups of 147 GWd/t and 162 GWd/t without any indication of fuel pin breaching. Structural components of these assemblies were made of modified Type 316 stainless steel and 15Cr-20Ni base advanced austenitic stainless steel. Post irradiation examinations of these assemblies revealed dimensional changes of fuel pins and assembly ducts due to irradiation-induced void swelling and irradiation creep, and fuel cladding local oval distortions due to bundle-duct interaction (BDI). The swelling resistance of 15Cr-20Ni base advanced austenitic stainless steel fuel pin cladding was almost the same as that of the modified Type 316 stainless steel cladding, while the assembly duct of the former material had slightly better swelling resistance compared with that of the duct of the latter material. Analyses of fuel pin bundle deformations indicated that these assemblies were likely to mitigate BDI mainly by fuel pin bowings and cladding oval distortions.