Apparatus for solidification of low- and medium-level wastes

Abstract

Solidification is a process of incorporating radioactive wastes into a solid insoluble matrix, which is the main barrier preventing radionuclides from escaping into the environment. Glass, ceramics, bitumen, cement (concrete), polymers, rubber, and so on can be used as the matrix.For medium-level wastes bitumenization and cementing processes are most widely used. In addition, for high-level wastes (10 -3 to i Ci/liter) a bitumen matrix is preferable because it is most stable with respect to leaching of radionuclides by ground waters. Up to 40-50 mass % of radioactive dry residue can be incorporated into a bitumen matrix and only 15-30% can be incorporated into a cement matrix. Above these percentages the stability of the matrix with respect to leaching drops sharply. Since a cement matrix, in contrast to a bitumen matrix, is noncombustible, in the last few years a great deal of attention has been devoted to cementing.The All of these setups are suitable for reprocessing bottoms, and the RB and KB bitumenizers can also be used to reprocess hydroxide, perlite, and ion-exchange resin sludges. Some models of all three types of bitumenizers have been checked on simulated wastes on stands at the SRICMM.A great deal of experience has been accumulated in operating setups with the RB and TB bitumenizers on real wastes. Setups with the RB-1000 bitumenizer with a capacity of 400 liters/h have been operating at the Leningrad nuclear power plants since 1984 (first setup) and since 1985 (second setup) and at the Ignalin nuclear power plant (Lithuania) since 1987. The setup with the RB-800 bitumenizer with a capacity of up to 250 liters/h has been operating since 1989 at the Kalinin nuclear power plant. On these setups the bitumen mixture is pumped into concrete compartments of the burial site, where it congeals. Setups with the RB-800 bitumenizers have been assembled at the Balakov, Roven, and Southern-Ukraine nuclear power plants. In these setups the bitumen mixture is packaged into 200-liter metal barrels. The TB-16 apparatus with a periodic-action bitumenizer with a capacity of 240 liters/h has been operating since 1978 at the Leningrad Special Industrial Group "Radon" (Sosnovyi Bor), where the burial site for the bitumen mixture is filled by pouring. The TB-and KB-type periodic-action bitumenizers with a complex of auxiliary equipment have been developed for a radiochemical plant. Setups with KB bitumenizers with a capacity of 40 liters/h have been produced for nuclear heat-generating plants.A diagram of a setup with a RB-800 bitumenizer is displayed in Fig. t. The bitumenizer 5 consists of a thin-film rotor evaporator with hinged paddles. The cubic residue and the bitumen are fed in a definite ratio by the pumps 1 and 4 with a regulatable flow rate from the tanks 2 and 3 into the bitumenizer where evaporation of the wastes and mixing with bitumen occur in a thin film. The bitumen mixture is fed by a double-auger Open-Type Joint-Stock Company "Sverdlovsk Scientific-Research Institute of Chemical Machinery Manufacture."

Inclusion of Radioactive Ion-Exchange Resins in Inorganic Binders

“…

This article is devoted to the inclusion of ion exchange resins in portland, portland blast-furnace, and alumina cements. Consequently, designs for reprocessing wastes at new power-generating units give preference to inflammable binders, primarily cement [2].Cementing differs advantageously from other methods of solidification by the simplicity of the apparatus used in the process and by the absence of any need for supplying heat and complicated gas purification. When 10 mass% clay is added to alumina cement, the diffusion coefficient of cesium decreases to 5.1·10 -6 cm 2 /day, and the volume of the wastes increases by not more than a factor of 1.5 on solidification.

Pulps of spent ion-exchange resins are a substantial radioactive component of liquid radioactive wastes produced during the operation of nuclear power plants.

…”

“…Consequently, designs for reprocessing wastes at new power-generating units give preference to inflammable binders, primarily cement [2]. However, in contrast to homogeneous wastes -bottom concentrates, bituminization of heterogeneous pulps of filtering materials on standard rotary-film bituminizers results in poor mixing, burn-ons, clogging of the equipment, and other difficulties.…”