The process of application of Best Estimate (BE) computer codes to the safety analysis of Nuclear Power Plants (NPPs) implies the evaluation of uncertainty. This is due with several causes connected with such codes and their use that includes the approximations in the constitutive equations, the numerical solution methods, the imperfect knowledge of boundary and initial conditions, nodalization and user effects, etc. The application of the BE SYStem (BE-SYS) codes with the connected uncertainty of the final results allows to provide a good view of existing margins or limits on NPP operation, consequently offering a basis for possible parameters optimizations, allowing the utilities to operate NPPs with the minimum cost and downtime. For this reasons, given the availability of mature codes for BE analysis and in the framework of the research of methods and tools for uncertainty evaluation, in the early ’90, UNIversity of PIsa (UNIPI) proposed a methodology, the Uncertainty Methodology based on Accuracy Extrapolation (UMAE), using measured and calculated data related to counterpart and similarity tests performed in Integral Test Facilities (ITF). The objective was to avoid or minimize the expert judgments. Some years later, following the experience of UMAE, a new method was developed. This method, the Code with the capability of Internal Assessment of Uncertainty (CIAU), aims at the objectives to reduce the dependence by the engineering judgments and the resources needed for the uncertainty evaluation. On the other hand, the application of the CIAU method implies the availability of a database constituted by a Quantity Uncertainty Matrix (QUM) and Time Uncertainty Vector (TUV) set up using qualified experimental data and qualified system code calculation results. This is the topic of this paper that describes the development of the database for the CIAU method application to CATHARE2 code. The activity and the methodology used are highlighted, including the main features of the database carried out in order to perform BE analysis and uncertainty evaluation with French ThermalHydraulic SYStem (TH-SYS) code.

Development of CIAU Database for NPP Safety Analysis by Cathare2 Code

D'AURIA, FRANCESCO SAVERIO
2007

Abstract

The process of application of Best Estimate (BE) computer codes to the safety analysis of Nuclear Power Plants (NPPs) implies the evaluation of uncertainty. This is due with several causes connected with such codes and their use that includes the approximations in the constitutive equations, the numerical solution methods, the imperfect knowledge of boundary and initial conditions, nodalization and user effects, etc. The application of the BE SYStem (BE-SYS) codes with the connected uncertainty of the final results allows to provide a good view of existing margins or limits on NPP operation, consequently offering a basis for possible parameters optimizations, allowing the utilities to operate NPPs with the minimum cost and downtime. For this reasons, given the availability of mature codes for BE analysis and in the framework of the research of methods and tools for uncertainty evaluation, in the early ’90, UNIversity of PIsa (UNIPI) proposed a methodology, the Uncertainty Methodology based on Accuracy Extrapolation (UMAE), using measured and calculated data related to counterpart and similarity tests performed in Integral Test Facilities (ITF). The objective was to avoid or minimize the expert judgments. Some years later, following the experience of UMAE, a new method was developed. This method, the Code with the capability of Internal Assessment of Uncertainty (CIAU), aims at the objectives to reduce the dependence by the engineering judgments and the resources needed for the uncertainty evaluation. On the other hand, the application of the CIAU method implies the availability of a database constituted by a Quantity Uncertainty Matrix (QUM) and Time Uncertainty Vector (TUV) set up using qualified experimental data and qualified system code calculation results. This is the topic of this paper that describes the development of the database for the CIAU method application to CATHARE2 code. The activity and the methodology used are highlighted, including the main features of the database carried out in order to perform BE analysis and uncertainty evaluation with French ThermalHydraulic SYStem (TH-SYS) code.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/116717
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