SEDL / STP / STP1175-EB / STP23979S

The Relationship of Grain Boundary Composition in Irradiated Type 304SS to Neutron Fluence and IASCC

Jacobs, AJ
GE Nuclear Energy, San Jose, CA

Pages: 17    Published: Jan 1994

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Abstract

Scanning transmission electron microscopy (STEM) analyses and HNO³/Cr⁺⁶ corrosion tests were carried out on irradiated Type 304 (UNS 530400) stainless steel (SS), in an attempt to correlate grain boundary composition with fast neutron fluence (E > 1 MeV) and irradiation-assisted stress corrosion cracking (IASCC) susceptibility. Test coupons originated from boiling water reactor (BWR) internals which had been fabricated from several heats of material. STEM and corrosion test results showed that cracking incidence in a crevice is independent of silicon and phosphorus segregation and chromium depletion, although still dependent on fluence. Grain boundary levels of silicon and phosphorus were influenced most strongly by the bulk values of these elements. In the commercial-purity (CP) heats having relatively high bulk values of silicon and phosphorus, marked segregation of these elements was observed with increasing fluence. The amount of chromium depletion tended to be greater in the CP heats than in a high-purity (HP) heat at higher fluences, and lower in the CP heats at lower fluences.