MICROSTRUCTURAL EVOLUTION OF PHOSPHORUS MODIFIED AUSTENITIC STEELS DURING IRRADIATION IN JOYO

The effects of phosphorus on microstructural evolution in austenitic stainless steels under fast neutron irradiation have been investigated. Three model alloys (Fe-16Cr-17Ni, Fe-16Cr-17Ni-0.024P and Fe-16Cr-17Ni-0.1P) were irradiated to 2 dpa and 11 dpa. The irradiation was performed in JOYO using SMIR-9. The nominal (calculated) irradiation temperatures were 673 (698), 773 and 873 K. Addition of phosphorus resulted in a suppression of void swelling at all temperatures except in 0.024P-alloy irradiated at 698 K to 11 dpa. The behavior of void swelling and phosphide formation by lower dose (2 dpa) irradiation was consistent with our previous studies of electron or high dose (40 dpa) neutron irradiations. In higher dose irradiation (11 dpa), on the other hand, void swelling and phosphide formation at 873 K were drastically suppressed. This may be caused by an unexpected temperature increase due to excess gamma-ray heating. A need for on-line temperature measurement and its active control are clearly demonstrated.