Annals of Nuclear Energy | 2021
Developing a method for time-variant reliability assessment of passive heat removal systems in nuclear power plants
Abstract
Abstract Nowadays, the use of passive safety systems is considered as the most important candidate to improve the safety level of new generation nuclear power plants. However, the functioning parameters of the passive systems vary significantly over time and are extremely tied to uncertainty. Time dependency may be due to the changes in certain and uncertain parameters and the mission of the passive systems. In this paper, a time-variant reliability analysis method that combines the out-crossing approach (PHI2) and the first-order reliability method (FORM) is developed and applied to analyze the passive heat removal system (PHRS) of VVER-1000 NPP as a case study. The thermo-hydraulic model of the PHRS and its related parameters besides the solving process of PHRS parameters in the PHI2 method are illustrated. The cumulative failure probability of the PHRS is calculated in terms of the system functioning parameters. The results of this study demonstrate that the failure probability of passive safety systems is significant in terms of amplitude and its variation over time and must be considered in the design and operation of these systems in the nuclear industry.