Inhibition of Radioactive Contamination of Stainless Steel in Boiling Water Reactor

Experiments were conducted to study the deposition kinetics of radionuclides on 304 stainless steel coupons since it has been assumed that exp 60 Co is the primary cause of radiation buildup. The coupons were treated by either passivation: exposed in 12% nitric acid at 50 deg C for 1 h; or preoxidation: exposed in pure water of 0.1 mu Si cm exp --1 , with 200 ppb dissolved oxygen, at 285 deg C for 25 approx 500 h. Coupons were exposed to neutral p H reactor water at 230 deg C containing 150-170 ppb O and flowing 0.5 m.s exp --1 for 25 approx 500 h. For exp 60 Co, no effects were observed on the passivated steel, but preoxidation remarkably inhibited the deposition of exp 60 Co because of the protective films. The exp 60 Co is assumed not to increase if the films fail to grow. Accumulation kinetics of exp 58 Co were similar to those for exp 60 Co. Results indicated that the incorporation of exp 51 Cr in oxide film was faster than that of exp 60 Co. The different kinetics are probably due to differences in the charges of the ionic species and of the oxide films. 8 ref.--MAY