Removal of ruthenium from high-level radioactive liquid waste generated during reprocessing of spent fuel

摘要

Radio-ruthenium (Ru) due to its existence in the form of complexes with varied oxidation state, larger fission yield and relatively long half life is an extremely troublesome nuclide during reprocessing and subsequent waste management. In the process of the concentration of high-level waste (HLW), containing many nitrates of fission products and nitric acid, Ru is oxidised to volatile tetroxide RuO_4, which is reduced to its dioxide (RuO_2) at the inner surface of the equipment and is deposited there. As a result, the radiation dose of the plant equipments keeps increasing. A process was developed for the separation of Ru from HLW stream by volatilisation using KMnO_4 (potassium permanganate) and O_3 (ozone) as oxidising agent and its subsequent trapping on adsorbent material polyether ether ketone pellets. Various parameters like acidity, Ru concentration, temperature, time period of reaction and type of adsorbent were studied. The sorption behaviour was examined with various isotherms like Langmuir, Freund-lich and Dubinin-Raduskevich isotherms. Thermodynamics parameters were also evaluated. The results indicated that maximum volatilisation of Ru occurred in the case of KMnO_4 (98%) as compared to O_3 (53%) at low acid concentration (2M).