Core concept of minor actinides transmutation fast reactor with improved safety

Fujimura, Koji*; Itooka, Satoshi*; Oki, Shigeo ; Takeda, Toshikazu*

A core concept of minor actinides (MAs)transmutation with improved safety was developed. Coresafety was improved by reducing sodium void reactivitywith sodium plenum and optimized configuration ofaxially heterogeneous core. "The effective void reactivity"by assuming the axial coolant sodium density changedistribution for ULOF (unprotected loss of flow) accidentwas introduced. MA content in the core fuel wasincreased up to 11 wt% for the condition that negativeeffective void reactivity was attained. Therefore, the largeMA transmutation amount which is almost two times tothe conventional Japanese fast reactor was obtained. Wealso conducted thermal hydraulics and fuel integrityevaluation of the core concept and it was confirmed thattheir results meet to the Japanese fast reactor designconditions. Finally we evaluated the transient behavior ofthe core concept and it was confirmed that this core hassluggish response during ULOF accident due to thenegative coolant reactivity effect of the upper sodiumplenum.