Experimental studies of applicability of the wet air oxidation for purification liquid radioactive waste

The scheme of handling with liquid radioactive waste (LRW) accepted to exploitation at atomic electric station (AWS) is often connected with evaporating technologies. In this case vat residues of evaporating systems with activity 105-106 Bq/1 and containing to 200-300 g/1 of salts are delivered up to LRW storages for lasting keeping. This schema does not correlate to the modern safety standards of handling with LRW, therefore at present numerous works are being carried on including those using technology of accumulated vat residues processing. Some successful experiments on sorption purification of high-salt LRW from cesium radionuclides giving the principal contribution into the total activity of a certain LRW are known. Unfortunately, attempts of sorption purification of the vat residues from other long-lived radionuclides (mainly from 60Co-radionuclide) were unsuccessful up to the present time. It is found with the fact that the vat residues contain a considerable amount of complexing agent producing stable complexes with transition metal radionuclides including those of 60Co. Extreme oxidation of the vat residues for decomposition of radioactive organic complexes is one of the solutions of this problem. The works related to oxidation of LRW including the AES vat residues with ozone, hydrogen peroxide as well as photo catalytic and electrochemical oxidation are known, however, possibilities of wet air oxidation (WAO) for LRW processing are not studied till the present time. Condition for decomposition of cobalt complex compounds and necessary excess of oxidizing agent may be easily attained with WAO usage. The necessary experiments were carried out at the experimental plant with the great interface surface (oxygen-solutions) equal to 400m-1 and 3 mm probe bed thickness. The heating time of the reactor to the working temperature 250 .deg. C did not exceed 50 seconds. 20... 50-fold oxidizer excess was achieved by the initial oxygen pressure into the reactor. The model solution with EDTA concentration close to that of the real one was used: 0,02N EDTA + CoCl2 excess + NaOH (4g/1) up to pH=12. It was found in result of investigation that decay of the complex and 60Co extraction is achieved 95% in 20 minutes. The residual equilibrium concentration is achieved in 120 minutes and equals to 0,5% of the initial one. The velocity constant k of the reaction in the range 0-20 minutes equals to 0,24