Vitrification of high-level wastes: A review of the computer thermal analyses for storage canisters

CANIST, a two-dimensional (r and θ) computer program that solves the unsteady-state, heat-conduction equation, was used to model the thermal behavior of canisters filled with waste glass. CANIST has been found to be a valuable analytical tool for predicting the temperature profile of a waste storage canister as a function of several variables, including the diameter of the canister, the placement of internal fins, the heat generation rate of the waste glass, and the thermophysical properties of the canister and the waste glass. Thus, temperature-dependent processes that may affect the integrity of the glass/canister unit, for example cracking, can be investigated using an analytical approach.     

Vitrification of a high-level iron-aluminate wastes simulator in a cold crucible

An increase of the water content of a simulator of sludges from the test area at the Savannah River Plant (USA) which are vitrified in a cold crucible with inner diameter 236 mm from 50 to 70 wt % results in a substantial reduction of the mass loading rate of the sludge, production of molten glass, and specific production of the glass product. The specific energy expenditures on vitrification increase by more than a factor of 2. The formation of an undesirable nepheline phase is observed in samples containing more than 60 wt % wastes simulator. The chemical stability of the glass product remains high even when its wastessimulator content is 65 wt %.     

Preliminary conceptual design of a geological disposal system for high-level wastes from the pyroprocessing of PWR spent fuels

The inventories of spent fuels are linearly dependent on the production of electricity generated by nuclear energy. Pyroprocessing of PWR spent fuels is one of promising technologies which can reduce the volume of spent fuels remarkably. The properties of high-level wastes from the pyroprocessing are totally different from those of spent fuels. A geological disposal system is proposed for the high-level wastes from pyroprocessing of spent fuels. The amount and characteristics of high-level wastes are analyzed based on the material balance of pyroprocessing. Around 665 kg of monazite ceramic wastes are expected from the pyroprocessing of 10 MtU of PWR spent fuels. Decay heat from monazite ceramic wastes is calculated using the ORIGEN-ARP program. Disposal modules consisting of storage cans, overpacks, and a deposition hole or a disposal tunnel are proposed. Four kinds of deposition methods are proposed. Thermal design is carried out with ABAQUS program and geological data obtained from the KAERI Underground Research Tunnel. Through the thermal analysis, the spacing between the disposal modules is determined for the peak temperature in buffer not to exceed 100 °C. Thermal analysis shows that the optimum spacing between the vertical deposition holes with 4 overpacks is 8 m when the disposal tunnel spacing is 40 m and optimum spacing of 2 m for horizontal disposal tunnel with 25 m tunnel spacing. Also, the spacing reduces to 6 m for vertical deposition when the double-layered buffer is used, which reduces the disposal area to one-sixty fifth (1/65th) compared with the direct disposal of spent fuels. Finally, the effect of cooling time on the disposal area is illustrated.     

Research and development of a high-efficiency one-stage melting converter-burial-bunker method for vitrification of high-level radioactive wastes

A new high-efficiency one-stage melting converter-burial-bunker method for vitrification of high-level radioactive wastes has been developed and investigated. The method includes evaporation (concentration), calcination, and vitrification of high-level radioactive wastes in a one-stage process inside a melting converter for non-metallic minerals, followed by burial inside a bunker-storage facility located directly underneath a melting chamber. Specific to the melting process is the direct combustion of a gas-oxygen-air mixture inside a melt. The experimental data for different aspects of the proposed method are presented, including converter/bunker dimensions, burner types and sizes, data for used materials, contents of saturated salty solution and final glass product, and entrainment analysis. The effective flue-gases cleaning systems and the design of the burial-bunker storage facility are also discussed.     

Experience in operating the ÉP-500/1R ceramic melter for vitrification of liquid high-level wastes

A. A. Bochvar All-Union Scientific-Research Institute of Standardization in Machine Building. Industrial Association “Mayak.” Scientific-Research Institute of Chemical Machine Building, Ekaterinburg. Translated from Atomnaya énergiya, Vol. 76, No. 3, pp. 183–188, March, 1994.     

The radiation swelling of bitumens and bitumenised wastes

Bitumens are used for the encapsulation of intermediate level radioactive wastes and as such are subjected to irradiation by the immobilised radionuclides. Gamma irradiation of bitumens and bitumenisates can result in considerable swelling through the radiolytic generation of gases which coalesce to form bubbles. Swelling is dependent on storage conditions such as dose rate, container size and total dose, and on material parameters such as type of bitumen and waste, and quantity of encapsulated waste. Prediction of swelling under storage conditions is important to ensure that the integrity of the container will be maintained, and also to enable the production of materials for laboratory measurements of radionuclide release. Radiation swelling has been measured for a wide range of bitumens and bitumenisates. Two theoretical models have been developed. The simpler model predicts that samples of a bitumenous material in geometrically similar containers of characteristic dimension L irradiated at dose rate I will swell the same amount for the same total dose provided IL² is the same for each of the samples. Bitumens and bitumenisates irradiated under IL² conditions corresponding to a storage condition equivalent to 200 1 containers containing an activity of ~ 1 Ci 1^?1 began swelling at around 5 Mrad and continued to around 100 Mrad. The smallest observed value of saturation swelling was around 10 vol.% for a highly filled, viscous bitumen, while other bitumenisates and bitumens swelled by several tens of per cent. A more complicated, bubble-growth model, considers the balance between gas production, bubble growth and gas escape. Good agreement was obtained between the experimental data and theoretical predictions of the bubble growth model. A consequence of the bubble growth model is that conditions of container size and contained activity can be defined that should produce little swelling.     

Immobilization of high-level wastes in stable mineral-like materials in a self-propagating high-temperature synthesis regime

The minerals which are most resistant to natural corrosive media and possess perovskite, zirconolite, fergusonite, and Y-Al garnet type structures are selected on the basis of an analysis of the mineralogical data. The minerals contain elements that are isomorphic to radionuclides appearing in high-level wastes. Synthesis of the analogs of calcinites, using metallothermal processes in a self-propagating high-temperature synthesis regime, was investigated on model systems in application to the immobilization of calcinates of high-level wastes. Compaction of the analogs of perovskite and zirconolite was investigated most completely, and the effect of various formulations and technological parameters on the process is studied. 3 figures, 2 tables, 6 references. Scientific-Research and Design Institute of Power Engineering. Translated from Atomnaya énergiya, Vol. 87, No. 1, pp. 57–61, July 1999.     

Vitrification of a surrogate for high-level wastes from the Savannah River facility (USA) in a commercial cold-crucible facility

Experiments on vitrifying a surrogate for SB2 pulp from the Savannah River facility (USA) in a cold crucible with inner diameter 418 mm in a commercial facility for vitrifying medium-level wastes at the Moscow Scientific and Industrial Association Radon are performed. Borosilicate glass materials, containing 50 mass % oxides of the wastes, including a magnetitic spinel phase in amounts not exceeding 15 vol. %, are obtained. The maximum mass average velocity of the slurry load and the melt output reach 40 and 16 kg/h, respectively. This corresponds to maximum specific vitrified wastes production capacity 2830 kg/(m²·day). The specific energy consumption for obtaining the glass product is about 10 kW·h/kg, which is approximately half the level for reprocessing slurries in crucibles with half the diameter. The chemical stability of the glass materials is 10–50 times higher than that of the materials made from glasses recommended by the US Environmental Protection Agency. __________ Translated from Atomnaya énergiya, Vol. 102, No. 5, pp. 296–299, May, 2007.