United States Nuclear Regulatory Commission - Protecting People and the Environment

Degradation of LWR Core Internal Materials Due to Neutron Irradiation (NUREG/CR-7027)

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Publication Information

Manuscript Completed: January 2010
Date Published: December 2010

Prepared by:
O.K. Chopra

Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439

A.S. Rao, NRC Project Manager

NRC Job Code N6818

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

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Abstract

Austenitic stainless steels are used extensively as structural alloys in the internal components of light water reactor (LWR) pressure vessels because of their relatively high strength, ductility, and fracture toughness. However, exposure to neutron irradiation for extended periods changes the microstructure and microchemistry of these steels and degrades their fracture properties. This report presents a critical assessment of the susceptibility of LWR core internal materials to irradiation effects such as irradiation-assisted stress corrosion cracking (IASCC), neutron embrittlement, void swelling, and irradiation-induced stress relaxation. The existing data, in the open literature as well as from research carried out by the U.S. Nuclear Regulatory Commission (NRC) and industry, have been evaluated to establish the effects of material parameters (such as composition, thermo-mechanical treatment, microstructure, microchemistry, yield strength, and stacking fault energy) and environmental parameters (such as water chemistry, irradiation temperature, dose, and dose rate) on these processes. Differences in radiation-induced degradation in material properties between light water reactors and fast-reactor irradiations are also discussed. The results are used to (a) define a threshold fluence above which irradiation effects on materials properties are significant, (b) develop disposition curves for cyclic and IASCC growth rates for reactor core internal materials, and (c) assess the significance of void swelling and irradiation creep relaxation on the structural and functional integrity of reactor internal components. The report also identifies potential deficiencies or knowledge gaps in the existing experimental data on degradation of LWR core internal materials due to neutron irradiation.

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