Advanced operation strategy for feed-and-bleed operation in an OPR1000

Abstract

When the secondary side is unavailable in a pressurized water reactor (PWR), heat from the core will accumulate in the primary side causing core damage. In this situation a heat removal mechanism called feed-and-bleed operation (FB operation) must be used, which is a process of directly cooling the primary reactor cooling system (RCS). However, conventional operation strategy in emergency operating procedures (EOPs) does not cover all possible conditions to initiate FB operation. If the EOP informs on the urgency of FB operation, operators will be able to more clearly make decisions regarding FB operation initiation. In order to cover all possible scenarios for FB operation and systematically inform its urgency, an advanced operating strategy using a decision tree is developed in this study. The plant condition can be classified according to failure of secondary side, RCS pressure condition, injectable inventory to RCS, and remaining core inventory. RCS pressure, core level, and RCS temperature are representative indicators which provide information regarding the initiation of FB operation. Indicators can be selected based on their detectability and quantification, and a decision tree is developed according to combinations of indicators. To estimate the effects of the advanced operation strategy, human error probability (HEP) of FB operation is re-estimated based on a thermohydraulic analysis. The available time for operators to initiate FB operation is also re-estimated to obtain more realistic data. This study is expected to provide a systematic operation strategy to initiate FB operation under various plant situations. An OPR1000 is used in this study as an example plant, with the resulting advanced operating strategy able to be applied to most PWRs which have FB operation capability.