Management of accumulated high level waste at the Mayak Production Association in the Russian Federation

At present, thousands of cubic metres of high level wastes (HLW) are stored at the Mayak Production Association (PA) in Ozersk, the Russian Federation. Despite fulfilling the required specifications, such a method of storage cannot be accepted as totally safe. Therefore. liquid HLW should be incorporated into a strong solid matrix. For this purpose, the HLW vitrification process is now implemented at the Mayak RA to produce phosphate glass blocks. The glass blocks in metallic containers are deposited to a storage facility. However, the accumulated liquid HLW contain large amounts of non-radioactive salts which increase costs at the stage of glass melting as well as in monitored storage of glass blocks. Besides, some HLW macrocomponents exert adverse effect on the process safety and on the resultant glass quality, Hence, it is appropriate to recover radionuclides from HLW bulk into concentrates of small volume for their subsequent solidification and to direct ballast mass to inexpensive near surface storage. For this purpose, at the Mayak PA an industrial facility combining the extraction and precipitation technology has been created. In the first stage. cesium and strontium are separated by chlorinated cobalt dicarbollyde (ChCoDiC). In the second stage. actinides and rare-earth elements (REE) are recovered by oxalate precipitation from raffinate. Towards the end of 2001, about 1200 m63 of HLW were reprocessed. In parallel with emptying the HLW tanks, the specific activity of glass blocks was doubled. The cost price of the vitrification process was reduced by 60%. Modernization of the technology involves elaboration of the all-extraction flowsheet. To accomplish this. the Radium Institute and the Mayak PA in collaboration with the Idaho National Engineering and Environmental Laboratory (INEEL), in the United States of America. have developed two alternative technologies. The first technology envisages the use of ChCoDiC for 9 recovery of cesium and strontium; actinides, REE and technetium are recovered by isoamyldialkylphosphine oxide. The second technology (the UNEX process) involves simultaneous recovery of cesium, strontium, actinides and REE from HLW This extractant is a mixture of ChCoDiC, carbamoylphosphine oxide (CMPO). and polyethylene glycol (PEG) in phenyltirufluoromethylsulfone (FS-13). The novel technologies were put through a series of tests on actual HLW Both processes afford recovery of long lived radionuclides by more than 99.9%. which enables the transfer of HLW bulk into a category of waste suitable for near surface storage.