Analysis of seismically induced core damage at two BWRs in the same site

二基隣接立地BWRプラントの地震起因炉心損傷への検討

村松 健; 劉 峭; 内山 智曜*

Muramatsu, Ken; Liu, Q.; Uchiyama, Tomoaki*

原子力発電施設のリスク管理への地震PSAの応用方法の検討を目的に、複数基立地サイトでの炉心損傷頻度や事故シーケンスの特徴及びアクシデントマネジメント方策としての電源融通の有効性について検討した。日本原子力研究所のモデルプラントの地震PSA(JAERI-Research 99-035)をもとにMark II型格納容器を有する隣接立地の2基のBWRを想定したシステムモデルを作成し、地震時のシステム信頼性解析用コードSECOM2を用い、炉心損傷頻度及び炉心損傷事故シーケンスの構成を求めた。また、事故シーケンス発生頻度の定量化では機器損傷の相関性が影響しうるので、感度解析により、その影響を考慮した。その結果、炉心損傷事故シーケンスの構成は、2基同時に炉心損傷となる場合より、1基のみ炉心損傷となる場合が多いことなどの結果を得た。さらに、電源融通に関する感度解析では、健全なユニットから損傷した側に融通することで、炉心損傷頻度を低下できる可能性のあることが示唆された。

Aming at proposing effective applications of seismic PSAs for design and risk management of nuclear facilities, a scoping study was conducted for seismic PSA of a multi-unit site to examine core damage frequency (CDF) and potential combinations of core damage sequences and the effectiveness of an accident management measure, namely, the cross connection of emergency diesel generators (EDGs) between adjacent units. Twin hypothetical units (BWR-5 with Mark-II Containment) located in the same site were taken as an example. The system model of these two units was constructed based on the Model plant (JAERI-Research 99-035). The CDF as well as the accident sequences was calculated by using SECOM2, a system reliability analysis code for seismic PSA study. In addition, since the frequency of an accident sequence was affected by the correlation of component failure, sensitivity analysis of the effect of correlation failure was performed. As a result on the accident sequences that cause core damage at this two-unit site, the contribution fraction of the cases of core damage at only one unit was higher than the fraction of cases of simultaneous core damage of both units. Further, it was suggested from the sensitivity analysis of cross-connection of EDGs between these two units that the cross connection would be an effective measure to reduce CDF of this two-unit site since the emergency power for the damaged unit could be supplied from the intact one.