Immobilization high-level waste

Hawkins, H. T., Sheetz, B. E. Gutrie, Jr., G. D. 1997. Preparation of monophasic (NZP) radiophases Potential host matrices for the immobilization of reprocessed commercial high-level wastes. Materials Research Society Symposium Proceedings, 465, 387-394. 

Hench, L. L., Clark, D. E. Campbell, J. 1984. High level waste immobilization forms. Nuclear and Chemical Waste Management, 5, 149-173. 

Cherniavskaya, N. E. 2000a. Phase compositions and elements partitioning in two-phase hosts for immobilization of rare earth - actinide high level waste fraction. Materials Research Society Symposium Proceedings, 608, 455-460. 

Weber, W. J., Ewing, R. C. et al. 1997. Radiation effects in glasses used for immobilization of high level waste and plutonium disposition. Journal of Materials Research, 12, 1946-1975. 

As a radiochemist, I would like to note the great significance of chemically bonded ceramics for high level waste (HLW) treatment. It is well known that for safe storage, transportation, and disposal of radioactive waste streams, it is necessary to convert them to hardened forms. Therefore, the search for and development of a new solid matrix for immobilization of HLW forms are important, indeed. 

Intermediate-level wastes (ILW) contain lower levels of radioactivity and heat content than high-level wastes, but they still must be shielded during handling and transport. Such wastes may include resins from reactor operations or solidified chemical sludges, as well as pieces of equipment or metal fragments. Commercial engineering processes are being used to treat and immobilize these wastes. Disposal options are similar to those for low-level wastes. 

This paper mentions the various modes now being considered for long-term storage of salt cake and encapsulated fission products. Processes to increase immobilization of the stored high-level waste are currently being developed status of the development work on these processes is also reviewed. 

It is thought that the scheme indicated in Figure 5 might provide as much as a 10-fold reduction in the amount of high-level waste to be immobilized and stored either on- or offsite. Needless to say, however, neither the technical nor economic feasibility of such a volume reduction scheme has yet been determined. 

The processes being developed at PNL convert the commercial high-level wastes to glasses or related ceramic forms. These materials offer the best practicable immobilization of radioisotopes, in a highly concentrated form, available today the AEG is also sponsoring continuing research on potentially more advanced solidified waste forms which may become available at a later date and offer added increments of safety or processing economy. 

To demonstrate that the various potential high-level waste compositions are all amenable to immobilization, the WFP program uses two standard waste compositions. These are a clean waste, designated PW-4b (which is essentially first-cycle raffinate), and a dirty waste (designated PW-6), which contains large amounts of sodium and iron see Table II). It should be noted that there are other possible constituents of high-level wastes, such as fiuoride, mercury, and soluble poisons which are not included in the initial demonstration program. 

The goal of non-high-level waste treatment is primarily volume reduction. This, however, does not hold for alpha-bearing waste, often called TRU waste. f Effective immobilization may... 

Volume reduction as described above usually leads to a product that still contains considerable quantities of water or that is quite easily leached or dissolved by water. The policy as to the degree of immobilization required for final disposal varies in different countries. As yet, there is no official regulation in the United States requiring that non-hi -level waste be inunobilized before disposal. It is, however, practiced in many places. In West Germany, by regulation, any non-high-level waste has to be immobilized before disposal in such a way that low leachability is warranted over a sufficient period of time. 

There is no doubt that immobilization at least of alpha-bearing waste must generally be required and will be in the future. It has been mentioned before that the total transuranic inventory of alpha-bearing non-high-level waste will be in the same order of magnitude as that of HLW. 

The range of suitable immobilization products for non-high-level waste is broader than that for HLW because there will be no significant heat generation. It includes glasses as well as cement, bitumen, and polymers. 

Rl. Richardson, G. L. Technologies for the Recovery of the Transuranium Elements and Immobilization of Non-High-Level Wastes, Proceedings of the International Symposium on the Management of Wastes from the LWR Fuel Cycle, Denver, 1976, Report CONF-76-0701, p. 289. 

The remaining liquid after Pu and U are removed is high-level waste (HLW), containing about 3% of the spent fuel. It is highly radioactive and continues to generate a lot of heat. This waste must be immobilized and because of the presence of radioisotopes with long half-lives it must be immobilized for tens of thousands of years. Ceramics are key materials in this process. 

The WVP process at Sellafield is specifically designed to vitrify High Level Waste from reprocessing operations at the site. As such, the borosilicate glass was formulated to provide the optimum properties for the incorporation and immobilization of calcined HLW. 

The vitrification process at Sellafield provides a proven safe route for the immobilization and storage of high level waste arising from reprocessing operations. 

The process for the manufacture of ceramics for immobilization of high-level wastes (HLW) as a rule is characterized by the following features ... 

Immobilization is also a current research activity. The proposal is to immobilize the resulting high level waste, or the remaining compound, using glass matrices based on niobium phosphate glasses, which can be melted in microwaves or in electrical furnaces. Three different samples of niobium phosphate glasses have been produced and sent for vapour... 

The recovery of U and Pu in the closed nuclear fuel cycle usually produces an high level waste (HLW) stream containing high concentration of fission/activation products (e.g., U, Pu, Am, Eu, Sr) and process/structural materials (Fe, Ni, Cr, etc.). This concentrated HLW is typically submitted to immobilization in glass/ceramic matrices, followed by their disposal in geological repositories. Considering the half-lives of the fission products (in the range of hundred-millions years) this solution result is unsustainable. The treatment of HLW by SLM represents a possible alternative. 

The immobilization of high level radioactive wastes using ceramics and glasses. Journal of Materials Science, 32, 5851-5887. 

Saether (1980), Saether Runnells (1980), and Stollenwerk Runnells (1981) studied the leaching of various retorting residues from US Green River oil shales. Alkaline pH values were established even before 25% of the first pore-volume had passed through the waste, and were maintained at high levels for the first 15 pore-volumes. The main potentially toxic elements mobilized under such alkaline conditions were found to be As, B, F, Mo, and Se. In contrast, base metals such as Cu, Ni, Pb, and Zn will be immobilized under such alkaline conditions (Baes Mesmer 1976 Bell 1976). 

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