United States Nuclear Regulatory Commission - Protecting People and the Environment

FAVOR Code Versions 2.4 and 3.1 Verification and Validation Summary Report (NUREG-1795)

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Publication Information

Manuscript Completed: July 2007
Date Published:
August 2007

Prepared by:
S.N.M. Malik

Division of Fuel, Engineering & Radiological Research
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Abstract

During plant operation, the walls of reactor pressure vessels (RPVs) are exposed to neutron radiation, resulting in localized embrittlement of the vessel steel and weld materials in the core area. If an embrittled RPV had an existing flaw of critical size and certain severe system transients were to occur, the flaw could very rapidly propagate through the vessel, resulting in a through-wall crack and challenging the integrity of the RPV. The severe transients of concern, known as pressurized thermal shock (PTS), are characterized by a rapid cooling (i.e., thermal shock) of the internal RPV surface in combination with repressurization of the RPV. Advancements in our understanding and knowledge of materials behavior, our ability to realistically model plant systems and operational characteristics, and our ability to better evaluate PTS transients to estimate loads on vessel walls led the U.S. Nuclear Regulatory Commission (NRC) to realize that the earlier analysis, conducted in the course of developing the PTS Rule (10 CFR 50.61) in the 1980s, contained significant conservatisms.

This report, which describes a summary of verification and validation (V&V) of the probabilistic fracture mechanics models in the Fracture Analysis of Vessels-Oak Ridge (FAVOR) code, is one of a series of 21 other documents detailing the results of the NRC study. The V&V involved assuring that the as-built software meets the requirements specified in the theory manual and the user's guide. The V&V activity involved development of test plans, test procedures, acceptance criteria for comparing the FAVOR-generated results with independent calculations, and test reports. The V&V team checked individual computational relationships for programming accuracy, but this V&V effort did not generally include a comprehensive, code line-by-line walkthrough. Based on the validation tests performed and reported results, the Nuclear Regulatory Commission concludes that the as-built software in version 3.1 of the code meets the requirements stated in the associated theory manual and the user's guide with reasonable confidence in the accuracy of the FAVOR-generated results.

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