Development of Inspection Guideline for Gas Accumulation in the Safety Systems

The Nuclear Regulatory Commission (NRC) in the United States has published twenty Information Notices, two Generic Letters, and one NUREG report related to this issue. Gas accumulation of approximately sixty events was reported for ten years since Generic Letter 2008-01 was issued. It has been considered that gas accumulation occurred since the beginning of commercial nuclear power plant operation and may occur in the currently operating plants. Gas accumulation in the safety systems is the condition that did not consider in Accident Analysis of Final Safety Analysis Report or Technical Specification and may finally result in degradation or loss of the safety functions. It is necessary and important to identify the status of gas accumulation in the operating plants. NRC issued a temporary inspection manual to provide background information and guidance for NRC inspectors on March, 2010. In this paper, Draft of inspection guideline for gas accumulation in the safety systems, which may give key precursors to prevent and to manage gas intrusion effectively, is proposed. Gas accumulation in the safety systems has been dealt with one of significant safety issues in the operating nuclear power plants. In order to identify the status of the accumulated gas, we proposed the draft of inspection guideline for gas accumulation in the safety systems. The proposed guideline provides specific inspection contents for safety system design and testing. This draft was modified and improved based on the result of the site inspection for Hanbit Unit 6. We think that this draft can be used to establish the regulatory position and procedure for gas accumulation inspection by KINS inspectors