A Study of Risk Evaluation Methodology Selection for the External Hazards

摘要

Since the accident at Fukushima Daiichi Nuclear Power plant caused by the Great East Japan Earthquake in March 2011, there has been growing demands for assessing the effects of external hazards, including natural events, such as earthquake and tsunami, and external human behaviours, and taking actions to address those external hazards. The newly established Japanese regulatory requirements claim design considerations associated with external hazards. The primary objective of the risk assessment for external hazards is to establish countermeasures against such hazards rather than grasping the risk figures. Therefore, applying detailed risk assessment methods, such as probabilistic risk assessment (PRA), to all the external hazards is not always the most appropriate. Risk assessment methods can vary in types including qualitative evaluation, hazard analysis (analyzing hazard frequencies or their influence), and margin assessment. The Risk Technical Committee of Atomic Energy Society of Japan comprehensively identified the external hazards which had potential risks bringing to the nuclear power plants, and has established the implementation standard for the identification of assessment methods for risks associated with external hazards. This paper discusses the comprehensive and systematic identification process described in the implementation standard which has potential risks leading to core damage, and the approaches of selecting an appropriate assessment method for each external hazard. This paper also describes some practical applications of specific risk evaluation methodology selection.