Recovery of 14C from graphite moderator of gas-cooled reactor (GCR)

The chemical exchange method of carbon isotopes between CO2 and carbamate was applied to the recovery of 14C from 1,600 t graphite moderator of a gas-cooled reactor (GCR), Tokai-1, and the dimensions of 14C-enrichment process were evaluated numerically. Applicability of two processes with different operation modes, continuous process and batch process, was discussed under the conditions that the concentration of 14CO2 in the stripped flow corresponding to 99% of feed CO2 is less than the environmental standard. For the continuous process using 2 mol/l diethylamine (DEA)-octane solution as a working fluid at -20degC and 0.2 MPa, the column dimensions were evaluated as 3.2 m in diameter and 5.7 m in height in the case of operating period of 20 yr. For the batch process using 4 mol/l DEA-octane solution, the column dimensions were comparable to those of continuos process, when the process was operated at the rate of 4 batch/month under the conditions of -20degC and 0.3 MPa. From these results, it is concluded that the CO2/carbamate exchange method is applicable to the recovery of 14C from irradiated graphite. However, the batch process has serious disadvantages, such as large energy consumption to maintain the top reservoir at low temperature and the generation of a large quantity of secondary wastes. At the present stage, the continuous process should be selected for the practical process design. (author)