A reliability assessment method for the VHTR passive safety systems

Abstract

The passive safety system of a 300MWt VHTR (Very High Temperature Reactor) which has attracted worldwide attention recently is actively considered for designing the improvement in the safety of the next generation nuclear power plant in Korea. The passive system functionality does not rely on an external source of the electrical support system, but on an intelligent use of the natural phenomena. It is not easy to evaluate quantitatively the reliability of the passive safety for the risk analysis considering the existing active system failure since the classical reliability assessment method could not be applicable. Therefore a new reliability methodology needs to be developed and applied for evaluating the reliability of the conceptual designed VHTR. The preliminary evaluation and conceptualization for the reliability are performed using the concept of the Load and Capacity theory related to the reliability physics model. The method using the response surface method (RSM) is also utilized for evaluating the maximum temperature of nuclear fuel in this study. The proposed methodology might contribute to evaluating the accident sequences and designing the new innovative nuclear system such as Reactor Cavity Cooling System (RCCS) in VHTR to be designed in future.