原子炉保護系ロジック盤の改造

Modification of logic module in the reactor protection system of JOYO

奥田 英一*; 長井 秋則*; 八木 昭*; 砂押 博*

not registered; not registered; not registered; not registered

原子炉保護系設備ロジック盤は,昭和52年「常陽」臨界以来,その安全保護機能に要求された性能を発揮してきた。しかし,設置以来,十数年を経て,システムの老朽化は否めず,保護系の信頼性,安全性の維持向上を目的とするロジック盤改造を実施するに至った。本報告書では,昭和60年常陽第5回定検の一環として実施した「ロジック盤改造工事」に関し,その改造に至った経緯・改造内容および成果等について報告する。以下に改造の結果得られた主な成果を示す。論理回路の使用IC素子は,耐ノイズ性に優れたC―MOSを採用した。又,論理回路および出力リレー回路設計には,フェイルセイフ思想の徹底を計り,原子炉保護系として,より高信頼性,安全性が実現できた。常陽で蓄積された運転,保守経験を生かし,事故時を含む考えられるプラントの挙動を十分に考慮した設計とした結果,従来より運転操作性が改善された。ロジック点検モードに手動点検を追加し,特定項目の診断が可能となった。又,論理回路,点検回路の異常監視機能を強化し,故障発先時に於ける補修の迅速,適確な対応が可能となり,メンテナビリティーの向上が計れた。

Since the initial criticality of Joyo was achieved in 1977, the reactor has been operated thoroughly and the reactor protection system which consists of control rods, acontrol rod drive system, monitoring instrumentations and logic modules has been functioned as designed. As the time elapsed, the maintenance work was gradually expanded due to degradation of the system. A modification of the logic module was conducted to increase its reliability. This paper describes the modification and its results of the logic module which was conducted during 5th periodical inspection. The logic module is essential for the reactor protection function, and provides scram signals on determing conditions. Reliability of the module is strongly required and function check of the module is also required on the reactor operation, for assurance of plant safety. The results of the modification are summerized as follows, (1)The solid-state integrated circuits used in the logic module as the basic logic switching scheme was modified from type "HTL" into type "C-MOS" which is excellent noise proof device. And further faile-safe design was completely applied in both logic circuits and out-put mechanical relay circuits. (2)Reflecting the experience obtained through the operation, the operational board and circuits were modified in order to improve operability of the system. New functions were introduced as indication of first actuated signal and self-testing circuits which enable to check regardless the operation conditions. Further step-wise checking was also introduced to diagnose integrity of individual signal train. (3)In order to increase maintenability, defect indication was newly provided, which displays circuit defect if any, and circuit boards were modified to access easily for checking.