Analysis of Risk-informed Safety Margin on SBO of Simplified Nuclear Power Plant Based on Monte Carlo Sampling

The risk-informed safety margin is a new safety concept of nuclear power industry in recent ten years. The calculation framework and the quantification technology under the Monte Carlo method of the riskinformed safety margin were studied. The riskinformed safety margin quantification technology of the station blackout (SBO) accident of nuclear power plant was focused on with the Monte Carlo sampling method. The simplified thermal hydraulic model of nuclear power plant was established with reference parameters of SBO accident in the simplified pressurized water reactor (PWR) model in the INL’s (Idaho National Laboratory) RISMC research. And the calculation process of the riskinformed safety margin based on Monte Carlo sampling method was determined. The number of scenarios generated by Monte Carlo sampling was essential to ensure the acceptability of the accuracy of the calculation results, and the accuracy of estimated value of probability safety margin would be higher if we establish more scenarios. The sampling times estimation method and the reliability calculation method of Monte Carlo were referenced, and a quantitative method of riskinformed safety margin with Monte Carlo sampling was proposed. The sampling times estimation method under the given error was given. According to the uncertainty calculation method of the riskinformed safety margin with Monte Carlo method and the estimation process of sampling times in Monte Carlo, the sampling times were determined by relative error and absolute error respectively. The results show that absolute error is equal to 001 with the 4 706 sampling times, and relative error is equal to 5% with the 9 604 sampling times in the riskinformed safety margin in SBO accident. The mean value and standard deviation of the failure probability of nuclear fuel cladding were calculated with these two sampling times. At this stage with the usual calculation of resource allocation, it is suggested that when the average failure probability of nuclear fuel cladding is larger than 01, the sampling times with 5% relative error should be selected. And when the mean value of failure probability of nuclear fuel cladding is equal to or lesser than 01, the sampling times with relative error equal to 10% could be used. The change of the mean value of failure probability of nuclear fuel cladding under the Latin hypercube sampling and random sampling method was studied. The relationship of the mean value with the recovery time of emergency diesel engine under different distributions was researched too. The calculation results indicate that the different sampling methods and different normal distributions have significant effects on mean value and standard deviation of the failure probability of the nuclear fuel cladding.