New thermo-plasma technology for selective 14C isotope extraction from irradiated reactor graphite

Abstract

We propose new thermo-plasma technology for the selective extraction of the radioactive isotope 14C in the deactivation treatment of the irradiated reactor graphite surface. The proposed technology has several advantages compared with other decontamination methods as it provides effective extraction of highly radioactive nano-micro-size layer from the surfaces of the graphite bulk via cathode plasma inert ion sputtering and compact collecting of the radionuclides via diffusion to anode. Thus it avoids formation of the liquid secondary radioactive waste (“dry” technology), the method is relatively simple to implement and can be technically and economically effective. For the decontamination of the graphite surface and concentrate of 14C exploration under the heating and plasma sputtering, the design of the plasma spraying cell is described. One of the problem to be traversed in this way is the presence of a number of other radioactive isotopes which must be separated from 14C enriched final product. It may be reached by thermal separation of different atoms presenting in the irradiated graphite in accordance with their individual rates for condensation from inert gas to anode substrate. For this purpose plasma sputtering cell includes elongated ceramic heat insulator elements at the heated inert gas pumping out tube to provide a number of zones with different temperature for separate spatial condensation, as well as a vacuum thermal insulation of the anode (collector) for the maximum temperature zone. Model of energy release in this plasma discharge was considered, heat flux via and temperature of the cathode (sputtered surface) and the anode were estimated to ensure pure carbon condensation on the anode excluding other radionuclide impurities.