Analysis of ULOF accident in Monju reflecting the knowledge from CABRI in-pile experiments and others

Sato, Ikken ; Tobita, Yoshiharu; Suzuki, Toru; Kawada, Kenichi   ; Fukano, Yoshitaka  ; Fujita, Satoshi; Kamiyama, Kenji  ; Nonaka, Nobuyuki; Ishikawa, Makoto; Usami, Shin 

In the first licensing procedure of the prototype FBR "Monju", the event sequence of ULOF (Unprotected Loss of Flow) was analyzed and the estimated mechanical energy was about 380 MJ as an isentropic expansion potential to atmospheric pressure. The prototype FBR has been stopped for more than 10 years since the sodium leakage accident in the secondary loop in 1995. The neutronic characteristics of reactor core changed as a consequence of radioactive decay of fissile Plutonium during this shutdown period. In order to assess the effect of this neutronic characteristics change to the mechanical energy release in ULOF, the event sequence of ULOF was analyzed reflecting the current knowledge, which was obtained by safety studies after the first licensing of the prototype reactor. It was shown that the evaluated mechanical energy release became smaller than 380 MJ, even with the change of neutronic characteristics.