Investigation on decontamination kinetics of metallic radionuclides in irradiated graphite by chlorination roasting

Abstract

Irradiated graphite used as moderator and reflector material in reactor core in nuclear industry is an important radioactive waste after reactor decommissioning. Treatment of irradiated graphite waste has been a challenge for IAEA member states. Chlorination roasting was proposed in order to remove the metallic radionuclides in irradiated graphite waste. The promising advantages of the proposed method include that the category of graphite waste can be reduced with near-zero carbon emission, and it can lead to potentially the recycling of irradiated graphite and metallic radionuclides. The decontamination kinetics of metallic radionuclides was evaluated based on a lab-scale tube furnace combined with density functional theory (DFT). 56Fe ions were implanted into nuclear graphite to simulate metallic radionuclides derived by neutron radiation. Decontamination efficiencies of Fe at 900, 1000, 1100, and 1200 °C for the retention time of 210 min were 42.6%, 81.6%, 94.4%, and 96.7%, respectively. Fe could volatilize from graphite in the form of complex metal chloride with retaining a large amount of graphite inert matrix. The decontamination process was described by the second order reaction model. Through DFT evaluation, Fe was chlorinated via Fe → FeCl → FeCl2 reaction pathway. This decontamination process is efficient, cost-effective, and reliable, which provide a valuable contribution to managing irradiated graphite.