Change of cation-exchange resin by heat in a simulated pressurized water reactor environment

Radiocarbon (¹⁴C) has been recognized as one of the most important radionuclides for the safety assessment of low level radioactive waste (LLW). Organic and insoluble carbons are generated in pressurized water reactors (PWRs) and these carbons may include ¹⁴C. Information is required on the mechanism of generation and the characteristics of these carbons so that safety assessments can be carried out appropriately and methods to reduce LLWs can be established. In this study, heating experiments were carried out on cation-exchange resin in a simulated PWR environment as a first step towards understanding the generation mechanism of organic and insoluble ¹⁴C and the characteristics of organic ¹⁴C as generated in a PWR. SO₃ detachment occurs from the resin and a structure similar to that of polystyrene was observed after heating for 24 h. This detachment was also observed after heating for 96 h; however, the main component of the heated sample changed to amorphous carbon under these conditions. Cation-exchange resins are believed to change to a similar structure to that of polystyrene by the detachment of SO₃. They then change to amorphous carbon by detachment of H and by carbonization with heating time. (author)