NON-METALLIC ALTERNATIVE SOLUTIONS FOR NUCLEAR COMPONENT LIFE EXTENSION

Abstract

This paper presents an overview of a feasibility study completed to assess the viability of Non-Metallic Repairs (NMR) specifically for use as a temporary solution to manage the Calandria Relief Ducts (CRDs) at the Bruce Nuclear Generating Station B (BNGS) Unit 7. The Unit 7 CRDs are constructed from 304L stainless steel. During plant operation, the CRDs are exposed to high levels of gamma and neutron radiation, humidity, and low levels of chlorides. It is believed that metal was impregnated with iron contamination during original construction. As a result, the CRDs have suffered degradation from chloride induced transgranular stress corrosion cracking (TGSCC). The NMR solutions (epoxy- and silicone-based) were assessed for their viability as a temporary solution to mitigate further degradation of the CRDs.

An environmental standard was developed leveraging data from plant operation, scrape sample analysis, and expected conditions within the CRDs. This standard established conservative environmental conditions (thermal, chemical, and radiological) against which the NMR materials were evaluated. The properties of the NMR materials were evaluated before and after various aging exposures (thermal, chemical, and radiological) and the results were used to inform relative projections of service life and assess the viability of these materials for the intended application.

While the NMR materials were ultimately concluded to be impractical for use in the CRDs, the development work created opportunities for future work applications in leak prevention and corrosion protection in conventional systems, decontamination, fuel bays, and other low radiation environments.