The Application of Fault Tree Method in Systematic Multiple Spurious Operation Analysis in Fire PSA

Systematic multiple spurious operation review is the important basement of Fire PSA Component Selection and Fire Induced Risk Modeling. It is a task of systematically evaluation of all plant systems and identification of equipments susceptible to potential spurious actuation that may challenge safe shutdown capability via spurious operations, which can ensure that the fire PSA model addresses the impacts of single spurious operations (SSOs) and multiple spurious operations (MSOs). In this paper, different methodologies of systematic multiple spurious operation review are studied and it is found that two methodologies are given in literature published at home and abroad: one methodology is development of comprehensive plant specific MSO list by panel review. This methodology is based on generic list of MSOs combined with plant specific information review. This methodology proposes high requirements for the expert panel and hard to avoid missing of some scenarios. Another methodology is review of all plant systems and components to receive SSOs, and then using MSO matrix to evaluate and encode each unique pair to receive MSOs that disable the system function. This methodology can ensure the integrity of MSO list, but the matrixes are too complicated. In this paper, the fault tree method is employed to improve the matrix method in the MSO evaluation process of the latter methodology. Reactor Coolant System (RCS) is taken as an example to describe the application of this method to CAP1000. Engineering practice shows that the fault tree method can effectively avoid omissions of MSO scenarios, and it is more useful and simple for tertiary or quaternary MSO evaluation, as well as more convenient for further MSO evaluation due to cross system issues. Furthermore, MSO fault trees can be directly called by fire PSA model for evaluation, which can lay a foundation for the follow-up work of fire PSA.