Multi-State Reliability for Pump Group in Nuclear Power System Based on UGF and Semi-Markov Process

In this paper,multi-state reliability value of pump group in nuclear power system is obtained by the combination method of the universal generating function（UGF） and Semi-Markov process.UGF arithmetic model of multi-state system reliability is studied,and the performance state probability expression of multi-state component is derived using semi-Markov theory.A quantificational model is defined to express the performance rate of the system and component.Different availability results by multi-state and binary state analysis method are compared under the condition whether the performance rate can satisfy the de-manded value,and the mean value of system instantaneous output performance is also obtained.It shows that this combination method is an effective and feasible one which can quantify the effect of the partial failure on the system reliability,and the result of multi-state system reliability by this method deduces the modesty of the reliability value obtained by binary reliability analysis method.