Recovery of ¹⁴C from Graphite Moderator of Gas-Cooled Reactor (GCR)

Abstract

The chemical exchange method of carbon isotopes between CO₂ and carbamate was applied to the recovery of ¹⁴C from 1,6001 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 2mol/l diethylamine (DEA)-octane solution as a working fluid at—20°C 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 continuous process, when the process was operated at the rate of 4 batch/month under the conditions of—20°C 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.

KEYWORDS:

• decommissioning
• graphite
• GCR type reactors
• carbon 14
• recovery
• isotope separation
• chemical exchange
• environmental protection
• process design
• continuous process
• batch process
• moderators