Analysis of abnormal operation procedures in sequences of loss of the RHRS at midloop operation

Several studies indicate the importance that the sequence of loss of residual heat removal system (RHRS) at midloop operation has in the global risk of the plant. In this sense, several simulations of loss of the RHRS with closed and open primary system with the TRACE V4.160 code have been performed considering different availability of steam generators. This paper aims to analyze not only the thermal-hydraulic behavior of the plant after the loss of RHRS, but also the interaction of the simulation results with the abnormal operation procedures and with the event trees of the sequences of loss of RHRS at midloop operation. The simulation results show that the main parameters depends on primary vent and the number of steam generators available. After a detailed study of phenomenology and abnormal procedures some modifications have been proposed in these procedures.