抄録
In nuclear power plant decommissioning, numerous metallic equipment, such as vessels, pipes and valves, is generated in the form of activated or contaminated waste. Such radioactive waste is expected to reduce its radioactivity via decontamination to become non-active waste.
Authors have developed a new chemical decontamination process for steel, especially carbon steel waste. The decontamination agent is formic acid, which easily decomposes into carbon dioxide and water. The optimum condition for carbon steel decontamination was proved to be 1.1mol·dm-3 of formic acid at 80°C. In the test for a heater tube under these conditions, the activity was reduced to below 0.4Bq·g-1 as 60Co after decontamination.
Organic carbon in decontamination solution could be decomposed to lower than 5mg·dm-3 (0.0004mol·dm-3 of formic acid) with hydrogen peroxide. The iron residue could be converted to iron oxide by evaporation and drying. Subsequently, the iron oxide was solidified by cement, with the mixing of a maximum of 120kg per 200-l drum.
Consequently, the newly developed decontamination process using formic acid is concluded to be applicable for the clearance of carbon steel waste.
