Nuclear power plant performance assessment pertaining to plant aging in France and the United States

Abstract

The effect of aging on nuclear power plant performance has come under increased scrutiny in recent years. The approaches used to make an assessment of this effect strongly influence the economics of nuclear power plant operation. This work aims (a) to determine how the risk-informed approach to performance assessment can be specifically improved, (b) to formulate and demonstrate a method for risk-informed nuclear power plant component reliability analysis, and (c) to assess the applicability of these improvements to the nuclear regulatory environments of the United States and France, the countries having the largest national nuclear power programs. In order to address the first objective, a case study of the U.S. and French regulatory treatment of the pressurized thermal shock phenomenon was performed. A new methodology that can be applied to the construction of risk-informed analyses was developed in response to the findings of the case study. The methodology specifically aims to improve upon current risk-informed methods, which implement a hybrid of best-estimate and conservative modeling, by increasing the use of risk-based modeling justification in order to allow for the development of a more logically consistent analysis. The second objective is addressed through the development of a new reliability model describing the effects of transient-induced degradation. The reliability model is applied through the demonstration of a risk-informed method for the calculation of fatigue degradation. The data requirements for the future successful implementation of this risk-informed method are presented. Examining the applicability of the risk-informed approach to U.S. and French nuclear power plant regulation showed that currently the U.S. is a more progressive implementer of risk-informed practices. This examination revealed, however, than an alternative approach known as the best-estimate plus uncertainty (BEPU) method could be considered for application in regulatory environments, such as in France, that are less accepting of the risk-informed approach. In order to understand how the BEPU method could be improved, the U.S. approach to BEPU was analyzed and recommendations for its future application are presented.