Environmental Degradation Issues to be Addressed for Ensuring Through-Life Performance of Materials in Advanced Reactors

Abstract of the technical paper/presentation presented at:
NEA Workshop on Regulatory Frameworks and Technical Approaches to Ensure Appropriate Qualification and Through-Life Performance of Materials in Advanced Reactors
June 3-5, 2025

Prepared by:
X. Wei, K. Kirkhope, and M. Hornof

Abstract

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section III, Division 5 provides rules for the design and construction of high temperature advanced reactors. This code does not cover deterioration that may occur in service as a result of radiation effects, corrosion, erosion, thermal embrittlement, or instability of the material. Division 5 is also clear that it is the Owner/Operator’s responsibility to demonstrate to the regulatory authority that these effects are accounted for in their specific reactor design.

It is anticipated that neutron irradiation of materials in high temperature advanced reactors may accelerate the material creep process and reduce material creep strength. Neutron irradiation may affect the time-dependent allowable stress values, including the temperature and time‐dependent stress intensity limit S_t, the design allowable value S_o, and the minimum stress‐to‐rupture strength S_r. There may also be an impact on the isochronous stress-strain curves and the material constitutive models for inelastic analysis. Under neutron irradiation, material creep could become significant even at a temperature below the threshold temperatures as defined in Division 5 Table HAA-1130-1. ⁵⁸Ni transmutation can cause significant irradiation damage in Ni-containing alloys for the components that are in service at high temperatures and are subjected to a high thermal neutron flux.

Corrosion processes can cause wall thinning, material embrittlement, and selective dissolution of material alloy elements into the environment. At the present, there is a lack of representative data for predicting material corrosion behavior in high temperature reactors. Selective loss of material constituent elements (such as C, Ni, Cr and Mn) may reduce the content of solid solution strengthening atoms, cause precipitate decomposition, and cause material phase transfer. These changes could reduce material strength, creep resistance, and materials stability, and thus affect the design parameters and allowable stress values for both time-dependent analysis and time-independent analysis.

The Canadian Nuclear Safety Commission (CNSC) expects the applicants to address these environmental degradation issues in the license to construct application for ensuring through-life performance of materials in high temperature advanced reactors.

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