Fracture failure analysis of steam generator channel heads with high carbon macro-segregation

Abstract

Fast fracture evaluation strategy is receiving earnest concern in the structural integrity analysis of nuclear equipment which subjected to the effects of neutron irradiation during operation. The increment of ductile and brittle transition temperature is mainly due to the neutron irradiation which increases the risk of brittle fracture failure. In addition to the neutron irradiation, the high carbon macro-segregation of low-alloy steels also increases the risk of brittle fracture failure as the carbon positive macro-segregation will lead to the increasing ductile and brittle transition temperature of low-alloy steels. In the present study, a conservative relationship between the carbon content and the increment of ductile and brittle transition temperature is developed based on data and is used to the brittle fracture failure analysis of the highest carbon content region in SG channel head. A special defect size is assumed considering capability of non-destructive evaluation technology in the brittle fracture failure analysis. Results show that ratio between the calculated stress intensity factor according to safety coefficient suggested by ASME design code and the critical stress intensity factor is less than one, which indicates a safe design and no risk of brittle fracture failure for steam generator channel head considering high carbon macro-segregation.