Development of the fast minimal cut sets calculation method for living PSA application; Improving the pre-deduced minimal cut sets method with success pass sets

Mihara, Takatsugu 

The plant configuration control system is being developed as one of the application of Living PSA. In order to evaluate risk measures, such as core damage frequency, among many kinds of plant configurations, shorter Boolean calculation time is favorable. One of the way to reduce the calculation time is the recalculation method based on the minimal cut set (MCS)data, not on the fault tree data. However, some of the truncated cut set terms may be important in some specific plant configurations. Therefore, this method has possibility to miss the important cut set terms and to get invalid risk measures. To avoid invalidity with this method, the way to improve the recalculation method was developed. The step of the development method is shown below. (1)Cut set data preparation. (a)For the safety systems to be evaluated, deducing the minimal pass sets that stand for minimal combinations of the support systems that are needed to make the safety system function. These minimal pass sets are represented in the form of boolean algebra using symbols that refer to the support systems. (b)Calculating the MCS data for the safety systems based on the each plant configuration identified with the each minimal pass set term. (2)Risk evaluation with specific plant configuration. (a)Any plant configurations to be evaluated can be represented in the from of the sum of the some minimal pass set terms identified above. Selecting the such minimal pass set terms matching the specific plant configuration to be evaluated. (b)Identifying the MCS data corresponding to the minimal pass set terms selected in the previous step. (c)Multiplying these MCS and simplifying with Boolean algebra, then we can get the MCS correspond to the configuration. Applying this method to the reliability analysis of the decay heat removal system of an LMFBR model plant, and compared with the fault tree calculation method, the validity of this method was assured.