Safety evaluation of prototype fast-breeder reactor; Analysis of ULOF accident to demonstrate in-vessel retention

高速増殖原型炉の安全評価; 炉容器内格納を示すためのULOF事故解析

鈴木 徹; 飛田 吉春; 川田 賢一   ; 田上 浩孝 ; 曽我部 丞司 ; 伊藤 啓

Suzuki, Toru; Tobita, Yoshiharu; Kawada, Kenichi; Tagami, Hirotaka; Sogabe, Joji; Ito, Kei

In the original licensing application for the prototype fast-breeder reactor, MONJU, the event progression during an unprotected loss-of-flow (ULOF), which is one of the technically inconceivable events postulated beyond design basis, was evaluated. Through this evaluation, it was confirmed that radiological consequences could be suitably limited even if mechanical energy was released. Following the Fukushima-Daiichi accident, a new nuclear safety regulation has become effective in Japan. The conformity of MONJU to this new regulation, hence, should be investigated. The objectives of the present study are to conduct a preliminary evaluation of ULOF for MONJU reflecting the knowledge newly obtained after the original licensing application, and to gain the prospect of In-Vessel Retention (IVR) for the conformity of MONJU to the new regulation. The preliminary evaluation in the present study showed that no significant mechanical energy release would take place, and that thermal failure of the reactor vessel could be avoided by the stable cooling of disrupted-core materials. This result suggests that the prospect of IVR against ULOF, which lies within the bounds of the original licensing evaluation and conforms to the new nuclear safety regulation, will be gained.