One of the main properties which guarantee safety of the storage, shipment, and burial of solidified radioactive wastes is their water resistance, which is determined mainly by the quantity of radionuclides which are transferred into a water medium when the water comes into contact with the compound. From this standpoint, the element cesium which forms easily soluble compounds is most dangerous. The content of this element in some types of wastes, for example, in salt ~oncentrates from nuclear power plants, is equal to 90% and higher of the total radioactivity. Simple cementing of liquid radioactive wastes containing cesium compounds does not fix the cesium reliably, and cesium can be almost completely leached out of small samples (8 cm 3 cubes) within several days on contact with water.The leaching of cesium from cement compounds can be decreased by two methods: preprocessing of the wastes in order to form insoluble cesium ferrocyanide or using sorption additives. The latter variant is cheaper and technologically simpler. Different types of clays, especially bentonites, have good sorption properties with respect to cesium [1][2][3][4]. However, introducing clay into a cement compound and at the same time improving its water resistance can change other properties of the compound. One such property, determining the safety of the handling of the wastes, especially at the stages of reloading and shipment, is mechanical strength. Another important parameter of cementing, which can be affected by the presence of clay in the mixture, is the plasticity of the cement test compound, characterized by the degree of cracking. Lower plasticity can lead to difficulties in preparing a homogeneous mixture and on loading it from the mixer into containers.Our objective in the present paper is to examine these questions. The main investigations were performed for salt concentrates from a nuclear power plant with a VVI~R reactor (Novovoronezh nuclear power plant) and a RBMK reactor (Leningrad and Kursk nuclear power plants). The water resistance was determined by the standard procedure (GOST 29114-91. Radioactive wastes. Method for measuring the chemical stability of solidified radioactive wastes by means of prolonged leaching). A comparative assessment of different materials was made according to the rate of leaching of radionuclides and the amount of radioactivity which has transferred into the water phase over a definite time interval.The results of tests on samples obtained by cementing salt concentrates from a nuclear power plant with a RBMK reactor are presented in Table 1. In these and subsequent tests Portland cement and slag Portland cement were used as binders and bentonite clay was used as a sorption additive. Adding to the binder bentonite clay in amounts of 5-10% by mass decreases the leaching of the radionuclides by a factor of 10, irrespective of the type of binder and the degree of filling of the compound within the limits investigated.The water resistance of cement compounds with salt concentrates from a nuclear pow...

621.039.7 As in most countries, in our country the concept of burial of low-and medium-level wastes near the surface, i.e., in burial sites located on the earth's surface or at a shallow depth, has been adopted for solidification of such wastes [1][2][3][4]. The solidified wastes placed in such burial sites can be influenced by a change in the composition of the water in contact with them, the variable temperature, the presence of microbiological action, and other factors.Radionuclides escape into the environment mainly because the solidified wastes come into contact with water, which can enter the burial site as a result of a leak in the site. In the process both ground water and surface water (rain or flood waters) can penetrate into the site. In addition, as the water passes through the shielding barriers, it will be enriched by the soluble components of the constructional and biospheric materials.A great deal of attention is being devoted to the study of the factors which influence the behavior of the solidified wastes stored near the surface or in the case of accidents during shipment [5][6][7].The effect of the composition of the contact water on the rate of leaching of the most mobile element -cesium from cement and bitumen compounds, which were obtained during solidification of salt concentrates formed during the operation of nuclear power plants with VVI~R and RBMK reactors, has been studied under laboratory conditions. The cement compounds were prepared using a mixture of Portland cement and bentonite clay in the ratio 9:1. The content of the dry residue of the wastes in the compound was equal to 15 and 30% for wastes from nuclear power plants with RBMK and VVI~R reactors, respectively. Distilled water [8], water which for a period of one month was in contact with the bentonite clay employed in burial sites as a buffer material, or with fragmented hard concrete, and water containing macrocomponents of the wastes leached out of the cement compounds were used as the leaching medium (Table 1). The rate of leaching of the cesium was determined by the method adopted in [8]. The investigations were performed on samples in the form of 8 cm 3 cubes.The results indicated a very small change in the amount of cesium arriving in the leach medium during the time of the experiment. The fraction of 137Cs leached out of the compounds with salt concentrates of a nuclear power plant with a RBMK reactor over a period of 159 days is equal to 3-7% for distilled water and 3-5 % for water in contact with the bentonite clay.Approximately 8% of the 137Cs in the distilled water, 7.5-8% in the water in contact with the bentonite, 11-12% in the water in contact with the hard concrete, and about 9% in the ground water was leached from the cement samples with salt concentrates from a nuclear power plant with a VVI~R reactor over a period of 14 days. As one can see, in this case the difference in the leach rate does not exceed 50%.Another factor that can affect the escape of radionuclides from cement compounds into the environmen...

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