Probabilistic safety Analysis for Assessing the Failure of Heat Removal Control of AP1000

Abstract

The safety level of nuclear power plant can be evaluated by using the adequacy of defence in depth that is implemented in the design. The defence in depth is to fulfill requirements of the fundamental safety function, which are reactivity control, heat removal control from the reactor, and confine control of radioactive material. Those controls shall be analyzed by probabilistic safety analysis. It is important to analyze the second fundamental safety function because the first fundamental safety function has a chance to fail. The purpose of this study is to calculate of the failure probability for the second fundamental safety function that is the heat removal control. The analysis is carried out by determining top event that is the change of heat removal control. Hereinafter, the intermediate events and the basic events are selected and the failure probabilistic is calculated using failure rate of component and human error. The AP1000 is used as the object of study. The generic data is collected from IAEA and other published documents. The results show that the probability of intermediate events are 5.52E-06 to 9.11E-04 per year and the total failure probability of the heat removal control is 1.89E-03 per year. Based on the assessment, it is concluded that the failure probability of the heat removal control is small enough and still within IAEA criteria.