EFFECT OF GAMMA-RAY IRRADIATION ON CORROS ION AND COBALT ACCUMULATIONOF TYPE-304 STAINLESS-STEEL IN HIGH-TEMPERATURE WATER IN THE PRESENCEOF ZINC ION

The effect of gamma irradiation on the corrosion and the cobalt accumu lation of type 304 stainless steel exposed to water at 561 K has been investigated. The exposure tests were carried out with and without the presence of 1.2 x 10(3) Gy/h gamma irradiation and 50 ppb zinc additi on. The structure and elemental depth distributions of the corrosion s urface were analyzed by EPMA, XRD and GDS. In the case of no zinc addi tion, the amount of corrosion did not appear to change with the gamma irradiation. However, the amount of crud release, the amount of corros ion film and the cobalt accumulation in the outer layer increased with the gamma irradiation. In the case of zinc addition, the amount of co rrosion and the corrosion film significantly increased and also the am ount of cobalt accumulation increased with the gamma irradiation. It i s considered that these differences are related to the reaction of met al ions and radiolysis products of water. On the other hand, the zinc addition suppressed the corrosion and the cobalt accumulation even wit h gamma irradiation. These suppression effects were reduced compared w ith the no gamma irradiation condition.