United States Nuclear Regulatory Commission - Protecting People and the Environment

Effect of Thermal Aging and Neutron Irradiation on Crack Growth Rate and Fracture Toughness of Cast Stainless Steels and Austenitic Stainless Steel Welds (NUREG/CR-7185)

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Publication Information

Manuscript Completed: September 2014
Date Published: July 2015

Prepared by:
Omesh K. Chopra

Argonne National Laboratory
Argonne, IL 60439

Appajosula S. Rao, NRC Project Manager

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

Cast austenitic stainless steel (CASS) materials and austenitic stainless steel (SS) welds, both of which have a duplex structure, are susceptible to thermal aging embrittlement during reactor service. In addition, prolonged exposure of these materials used in core support structure and reactor internals to neutron irradiation changes their microstructure and microchemistry, which further degrades their fracture properties. The core support structures and reactor internals also contain austenitic SS welds. The purpose of this effort was to review and evaluate the existing thermal aging and neutron irradiation embrittlement data on these materials to update the methodology developed earlier at Argonne National Laboratory (Argonne) for estimating the degradation of mechanical properties of these materials during reactor service. The methodology developed earlier in NUREG/CR-4513 Rev. 1, 1994, to determine the kinetics and extent of thermal embrittlement from known material information as a function of time and temperature of service, has been reviewed and, where necessary, updated to incorporate recent data published after the NUREG/CR-4513 Rev.1 report was published. The updated methodology is used to estimate the fracture toughness J-R curve of thermally aged CASS materials as a function of time and temperature of service. The existing data on irradiated materials were also evaluated to define a threshold fluence level above which irradiation effects on materials properties are significant. This report also examines the combined effects of thermal and neutron embrittlement, which can degrade the fracture toughness of these materials more than predicted from either of the processes independently. Potential information gaps in the data needed to adequately address the effects of thermal aging and neutron irradiation on fracture properties of CASS materials and austenitic SS welds were identified.

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