The importance of molybdenum on irradiation assisted stress corrosion cracking in austenitic stainless steels
- ABB Atom, Vaesteraas (Sweden)
- Nuclear Electric, Berkeley (United Kingdom). Berkeley Technology Centre
Constant extension rate tensile (CERT) specimens were irradiated in the core of a commercial operating BWR. Subsequently to irradiation, CERT testing was performed in a test loop attached to the reactor water clean-up system in the same BWR, using reactor water at a high flow rate. Testing was performed in BWR normal water chemistry (NWC), and BWR hydrogen water chemistry (HWC). Type 316 SS was much less susceptible to IASCC than Type 304 SS in both NWC and HWC. In addition, high purity (HP) Type 304 SS was more susceptible to IASCC than commercial purity (CP) Type 304 SS in NWC at intermediate fluence. The results suggest that chromium depletion due to radiation induced segregation (RIS) is an operating mechanism in NWC, and the only one of importance at fluences below 3 {center_dot} 10{sup 21} n/cm{sup 2}. At higher fluence another mechanism supervenes. Detailed microchemical analysis was conducted on unirradiated archive material and irradiated material. Two complementary techniques were used, field emission gun scanning transmission electron microscopy and Auger electron spectroscopy. The unirradiated materials showed nonequilibrium segregation of chromium, molybdenum and phosphorus. Irradiation to intermediate fluences resulted in further enhancements, of silicon and phosphorus, at the grain boundaries. In the CP materials, molybdenum and chromium remained enhanced at the grain boundaries with chromium depletion on either side of the grain boundary, while chromium was significantly depleted in the HP material. At higher fluences chromium was significantly depleted in the CP Type 304 SS material. Molybdenum seemed to retain the chromium level at the grain boundary during irradiation up to a certain fluence. For the HP Type 304 SS material, which contained virtually no molybdenum, the chromium level was lower than for the CP heats.
- OSTI ID:
- 367708
- Report Number(s):
- CONF-960389--
- Country of Publication:
- United States
- Language:
- English
Similar Records
Grain-boundary microchemistry and intergranular cracking of irradiated austenitic stainless steel
Irradiation-assisted stress corrosion cracking of materials from commercial BWRs: Role of grain-boundary microchemistry