Release and deposition of corrosion products in a simulated BWR coolant system

Information on corrosion products release from structural material is useful for radiation control in reactor coolant systems. The influence of dissolved oxygen on corrosion products release from AISI 304 stainless steel was studied in high purity water from 30 deg C to 280 deg C which corresponds to the state of BWR coolant system. The release rates of Fe, Ni and Co from stainless steel increased as the temperature was raised from 30 deg C and reached the maximum at about 200 deg C, then decreased as the temperature was raised. Their release rates were reduced by the addition of dissolved oxygen in about 100 μg/kg at the temperatures in this experiment. On the other hand, the release rate of Cr was maintained at low levels at temperature up to 280 deg C, when the concentration of dissolved oxygen was below 1 mg/kg. With the concentration of dissolved oxygen exceeding 1 mg/kg, the Cr was released as chromium anion, especially at high temperatures. This release behavior was possibly caused by the dissolution of chromium-rich films. Accumulation of ionic Co on the zircaloy surface was examined under simulated BWR primary coolant condition using 58Co as a tracer. Among Fe, Cr and Ni components, Cr component showed highest deposition rate on the zircaloy surface. 58Co was likely to be present in this Cr deposits. The rate of 58Co accumulation was reduced on the pretreated zircaloy with overheated steam to form stable ZrO2 films. Behavior of ionic Co can be explained by the interaction with Cr component. (author)