Evaluating thermo-hydraulics uncertainties of success criteria in probabilistic risk assessment

摘要

Success criteria analysis in nuclear power plants is based on thermo-hydraulics (TH) evaluation of the plant response to postulated accidents for the development of a risk model. PRA (Probabilistic Risk Assessment) uncertainties originate from diverse sources, including uncertainty of success criteria. A comprehensive uncertainty treatment methodology is therefore needed for the quantification of PRA uncertainty considering the success criteria uncertainty. This paper covers the topic and introduces a systematic framework for this purpose. The proposed methodology is capable of including model uncertainty of success criteria in the plant risk model which is not formally performed in industrial practice. An extension is proposed for the traditional event trees to include a new top event for taking the effect of TH uncertainties into account. The required probability density function for this top event is obtained by performing TH uncertainty analysis and statistical interpretation of the obtained results. The application of the methodology is sought by its implementation on real case of loss of coolant accident in a PWR type nuclear power plant.