Development of a suppression method for deposition of radioactive cobalt after chemical decontamination: (III) the suppression mechanism with preoxidized ferrite film for deposition of radioactive cobalt

Abstract

The Hitachi ferrite coating film process (Hi-F) has been developed to lower recontamination after chemical decontamination. In this process, the chemical decontamination process is carried out, and a fine Fe 3 O 4 coating film is formed on the surface of stainless steel piping in an aqueous solution. In order to improve the suppression of 60 Co deposition further, we combined the original Hi-F with a preoxidation step. We found the deposited amount of 60 Co with preoxidized Hi-F coating film (OHi-FC) was 1/10 of that for non-coated specimens. In this study, we investigated the suppression mechanism of 60 Co for the OHi-FC. The composition of OHi-FC was changed from Fe 3 O 4 to Fe 2 O 3 and then the crystals in the OHi-FC grew three times larger than those of the original Hi-F coating film. Consequently the corrosion amount of the stainless steel base metal was reduced by getting larger grains in the coating film. Because 60 Co was incorporated into the corrosion oxide, the suppression effect of 60 Co deposition by preoxidation was attributed to the suppression of the formation of the corrosion oxide by the OHi-FC.

Investigation of cobalt buildup behavior and suppression by zinc injection on stainless steel under HWC conditions using simultaneous continuous measurements of corrosion and cobalt buildup

“…The oxide films incorporating the radioactive species grow on the surface of the components, and so become a radiation source [1]. Since cobalt-60 ( 60 Co) is the main radioactive nuclide associated with this radiation source, some research groups have been developing countermeasure technologies for the 60 Co buildup on the surface of the components and have been studying the mechanisms of 60 Co incorporation into the oxide films [2][3][4][5][6][7].…”