Comparison between Best-Estimate–Plus–Uncertainty Methods and Conservative Tools for Nuclear Power Plant Licensing

Abstract Computational reactor safety analysis is trending to replace conservative evaluation model calculations with best-estimate analysis complemented by uncertainty evaluation of the code results. In such cases, the evaluation of the margin to acceptance criteria (e.g., the maximum fuel rod clad temperature) is based on the upper limit of the calculated uncertainty range. Uncertainty analysis is compulsory if relevant conclusions are to be obtained from best-estimate thermal-hydraulic code calculations in order to avoid presenting single values of unknown accuracy for comparison with regulatory acceptance limits. This paper, after a thorough introduction of conservative and best-estimate methods and characterization of the main sources of uncertainties affecting best-estimate system codes, applies a best-estimate-plus-uncertainty (BEPU) method to three cases having as reference different nuclear power plants and different types of transients. Finally, the results from the BEPU approach is compared with a conservative approach and a combined approach.

[1]  Francesco Saverio D'Auria,et al.  CSNI Code Validation Matrix of Thermo-Hydraulic Codes for LWR LOCA and Transients , 1987 .

[2]  Lawrence E. Hochreiter,et al.  Application of code scaling applicability and uncertainty methodology to the large break loss of coolant , 1998 .

[3]  R. P. Martin,et al.  Development Considerations of AREVA NP Inc.'s Realistic LBLOCA Analysis Methodology , 2008 .

[4]  Francesco Saverio D'Auria,et al.  Confirmatory Safety Analyses carried out by Relap5 and Cathare codes related to the Kozloduy VVER 440/230 unit No. 3 , 2001 .

[5]  M G Ortiz,et al.  Uncertainty analysis of minimum vessel liquid inventory during a small-break LOCA in a B W Plant: An application of the CSAU methodology using the RELAP5/MOD3 computer code , 1992 .

[6]  Alessandro Petruzzi,et al.  Methodology of Internal Assessment of Uncertainty and Extension to Neutron Kinetics/Thermal-Hydraulics Coupled Codes , 2005 .

[7]  Francesco Saverio D'Auria,et al.  Planning of Counterpart Tests in LWR Experimental Simulators , 1988 .

[8]  Francesco Saverio D'Auria,et al.  Separate Effects Test Matrix for Thermal-hydraulic Code Validation: Facility and Experiment Characteristics,Vol II , 1993 .

[9]  F. D'auria,et al.  Outline of the uncertainty methodology based on accuracy extrapolation , 1995 .

[10]  I. Catton,et al.  Quantifying reactor safety margins part 1: An overview of the code scaling, applicability, and uncertainty evaluation methodology , 1990 .

[11]  Alessandro Petruzzi,et al.  RELAP5 simulation of surge line break accident using combined and best estimate plus uncertainty approaches , 2009 .

[12]  Francesco Saverio D'Auria,et al.  Development of a Code with the Capability of Internal Assessment of Uncertainty , 2000 .

[13]  Horst Glaeser,et al.  GRS Method for Uncertainty and Sensitivity Evaluation of Code Results and Applications , 2008 .

[14]  Cesare Frepoli,et al.  An Overview of Westinghouse Realistic Large Break LOCA Evaluation Model , 2008 .

[15]  Maria Regina Galetti.  Regulatory Scenario for the Acceptance of Uncertainty AnalysisMethodologies for the LB-LOCA and the Brazilian Approach , 2008 .

[16]  Bucalossi Andrea,et al.  Current Use of Best Estimate plus Uncertainty Methods on Operational Procedures Addressing Normal and Emergency Conditions , 2008 .

[17]  H. Eichhorn,et al.  Accident analysis of nuclear power plants , 1973 .

[18]  Jinzhao Zhang,et al.  Application of the W̱COBRA/TRAC best-estimate methodology to the AP600 large-break LOCA analysis , 1998 .

[19]  PART 50—DOMESTIC LICENSING OF PRODUCTION AND UTILIZATION FACILITIES , 2010 .