Best Estimate Safety Analysis For Nuclear Power Plants: Uncertainty Evaluation

摘要

There are a number of IAEA publications devoted to the qualified use of advanced computer codes for safety analysis. The objective of this report is to provide practical guidance for the evaluation of uncertainty as a necessary component of BE safety analysis and to encourage the broader use of this approach. Such guidance is considered most important to avoid misinterpretation of calculation results and an unjustified reduction in safety. The main use of the BE of safety analysis and, consequently, of this report is expected to be in applications for design and licensing purposes, both for new reactor projects and for periodic safety reviews, safety upgrading and lifetime extensions of existing nuclear power plants. Uncertainties considered in the IAEA safety standards and other guidance publications are summarized in Section 2. Various options for combining computer codes and input data for safety analysis are also discussed. Section 3 provides an overview of uncertainty methods (i.e. classification of the methods, propagation of input uncertainties, extrapolation of output error, etc.). Probabilistic and deterministic methods are introduced for the propagation of input uncertainties. Basic features of uncertainty methods that are representative of the classification of the methods are compared. Steps to ensure adequate uncertainty evaluation methods are discussed in Section 4. Code adequacy, the code application user effect, platform independence and qualification of the methods are considered as major topics. Section 5 suggests various application methods for uncertainty evaluation. This section describes the basic steps in the process, characterization of the scenario, selection of the code, the nodalization process, selection of the uncertainty quantification process and the application of the uncertainty process.