Various cast austenitic stainless steels composed of austenite and ferrite phases are used for primary pressure boundary components such as main coolant loop piping, pump casings and so on in old PWRs. However, these components have been known to experience a loss of fracture toughness caused by thermal aging embrittlement, when exposed to reactor operating temperatures over a long period, that may lead to failure. The purpose of this paper is to introduce the major component status, thermal aging embrittlement susceptibility, material property change determination, flaw evaluation methods, case studies considering the thermal aging embrittlement phenomenon and future plan of Korean industry. The tentative results showed that the thermal aging embrittlement is a plausible age-related degradation mechanism, thereby its effects should be managed adequately in order to sustain the integrity of the corresponding components.

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