Performance analysis of the SPRHRS for the 1000 MWe class PWR in coping with station black out

Abstract

In order to improve the safety and reliability of the Chinese nuclear power plants (NPP), an innovative passive nuclear safety design, the secondary passive residual heat removal system (SPRHRS) is proposed for the light water reactors in China. Previous research work has shown that under design-basis accidents, SPRHRS can mitigate the results by partially or completely replacing the traditional emergency water cooling system. However, the Fukushima Daiichi nuclear power plant accident implies necessity of further assessments of NPPs capability to withstand threats resulting from accidents beyond design-basis accidents. In this study, the nodalization of a 1000 MW class PWR with the SPRHRS design was conducted using RELAP5/MOD3.4. Responses of the PWR under the loss of heat sink accident caused by the station blackout (SBO) was analyzed. The results showed that the residual heat can be effectively removed by the SPRHRS under SBO. In addition, sensitivity studies about the effects of the coolant tank volume and the isolation valve opening condition of the SPRHRS on its residual heat removal capability were also performed. The results indicate that these two main design elements have significant influence on the operation characteristics of SPRHRS. For the SPRHRS design in this study, the appropriate value of the coolant tank volume is 400 m3 and the appropriate valve opening signal is set to be triggered when the SG shell side collapsed liquid level drops lower than 20% of its full value. The present work would be instructive for the design of passive safety systems of Chinese NPPs.