Approach To Handling Epistemic Uncertainty While Processing Risk Informed PCT Safety Margin Characterization

Nuclear energy power generation has been regarded as an important part of the future energy supply;the method which is used for evaluating safety of nuclear power plants gets much improved continuously along with the development of science and technology.The initial nuclear plant safety evaluation system was based on a deterministic analysis system which is conservation enough.Towards design basis accidents,the initial events should be sorted out and the initial condition?boundary condition and the model hypothesis of the system would be set to be conservation enough.If the final computational result complies with laws and regulations,the design of the nuclear plant would be considered be safe,the difference between the computational result and index value would be regarded as safety margin.In the to-be-issued 10 CFR 50.46 a,the large break loss of coolant accident will be categorized as accidents beyond design basis and the peaking cladding temperature(PCT)margin shall be evaluated in a risk-informed manner.Risk informed safety margin characterization integrates best-estimate plus uncertainty quantification with probabilistic safety assessment,which can reasonably quantify the aleatory uncertainty and epistemic uncertainty while processing risk informed peak cladding temperature safety margin characterization.Based on probabilistic safety assessment,Potential accidents sequences during the period of running and corresponding probability of occurrence can be figure out.Then the probability significant sequences will be choose,the best-estimate plus uncertainty quantification method will be used to reasonably quantify the uncertainty of calculation.Ultimately,the safety margin of the nuclear plant during the period of running will be more reasonably calculated.In this article,a risk informed safety margin characterization process has been suggested to quantify the risk-informed PCT margin,which is based on the large break loss of coolant accident of a typical three loops pressurized water reactor.Random failures of system and components derived from aleatory uncertainty can be evaluate by probabilistic safety assessment,and epistemic uncertainty can be measured by random sampling method based on best-estimate plus uncertainty quantification.To reasonably quantify risk informed PCT safety margin,the top three probability significant sequences and the licensing sequence shall be chosen for studying based on the result of probabilistic safety assessment.By comparing with the traditional deterministic methodology,it can be found that the PCT margin evaluated by the risk informed safety margin characterization methodology can be greater by 26.67~61.47 K.