Abstract60Co accumulation on boiling water reactor (BWR) primary cooling pipings. To demonstrate the treatment effect, test specimens, which had been exposed to simulated BWR water in an autoclave (temperature, 286°C; pH, 7; oxygen concentration, 200 ppb) for up to 200 h, were installed in the Hatch-2 inplant loop and their60Co deposition amounts were compared with those of as-received specimens. Preoxidation treatment for 200 h resulted in deposits of about one-fourth those of as-received specimens. It was estimated that the maximum amount of60Co deposited on primary piping during the entire plant operation life (30 yr) would be reduced to about one-half of that without preoxidation treatment if the60Co concentration in the reactor water was constant.