An Analysis of CDA event sequences in lead-bismuth cooled fast reactor

鉛ビスマス冷却高速炉における炉心崩壊事故の事象推移解析

飛田 吉春; 山野 秀将   

Tobita, Yoshiharu; Yamano, Hidemasa

鉛ビスマス冷却MN(混合窒化物)燃料高速炉のULOF事象解析を実施し、重金属冷却高速炉の炉心損傷事故における事象推移特性と支配現象を明らかにした。鉛ビスマス冷却MN燃料高速炉の炉心損傷事故では、燃料スウェリングによる燃料浮上の有無が事象推移に大きな影響を与えることが示された。今後は、現在JAEAが実施しているNifti試験の知見から得られる窒化物燃料の燃料スウェリング特性を評価に反映する予定である。また、核的事象終息後の崩壊熱除去過程の評価を進め、事故影響の炉内格納性の検討を行う。

The present study is intended to draw a rough sketch of CDA event sequences, to understand the characteristics of CDA, and to judge whether the measures to eliminate energetic recriticality are necessary or not for a LBE-cooled fast reactor. The present analysis has analyzed a LBE-cooled mixed-nitride (MN) fuel reactor with 1875 MWth. In this study, an unprotected loss-of-flow (ULOF) with flow having time of 10.0 s has been chosen as a representative CDA initiator. In the analysis, the loss-of-flow event has been simulated by the reduction of inlet pressure, following a quasi steady-state calculation with nominal full power and flow rate. This analysis has showed that the swelling of fuel pellets is the key phenomenon during the CDA of LBE cooled fast reactor. The further accumulation of experimental knowledge on the swelling behavior of fuel, especially for nitride fuel, is essential in improving the accuracy and reliability of CDA analysis.