Dynamic risk assessment under design extension conditions

Abstract

Recently, there is an approach to introduce the design extension conditions, which exceeds the design basis accidents, into the design and operation procedure of nuclear power plant, but there is absent of an appropriate safety assessment methodology under the design extension conditions. Therefore, in this research, a dynamic risk assessment methodology was suggested to support a rational decision making for the safety enhancing follow-up measures by assessing the comprehensive effect of design and operating parameters, and reliability of system and operator action in terms of risk. The accident with complex seqeunces, which assumes multiple failures of engineered safety features, is subject to the dynamic risk assessment methodology. In this research, the theoretical basis on a series of process for unifying the comprehensive safety assessment results into the dynamic risk information was delineated, and a case study was performed on a containment bypass accident. The dynamic risk assessment results presented that the emergency operator action for a prevention of large early release was judged to be not credible on the basis of the statistical inference, so that the reliability enhancement on auxiliary feedwater system turned out to be in the first priority.