The presence, diversity, and geochemical activity of microorganisms in the Severnyi repository of liquid radioactive wastes were studied. Cultivable anaerobic denitrifiers, fermenters, sulfate-reducers, and methanogens were found in water samples from a depth of 162-405 m below sea level. Subsurface microorganisms produced methane from [2-(14)C]acetate and [(14)C]CO(2), formed hydrogen sulfide from Na(2) (35)SO(4), and reduced nitrate to dinitrogen in medium with acetate. The cell numbers of all studied groups of microorganisms and rates of anaerobic processes were higher in the zone of dispersion of radioactive wastes. Microbial communities present in the repository were able to utilise a wide range of organic and inorganic compounds and components of waste (acetate, nitrate, and sulfate) both aerobically and anaerobically. Bacterial production of gases may result in a local increase of the pressure in the repository and consequent discharge of wastes onto the surface. Microorganisms can indirectly decrease the mobility of radionuclides due to consumption of oxygen and production of sulfide, which favours deposition of metals. These results show the necessity of long-term microbiological and radiochemical monitoring of the repository.

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Deep burial of liquid radioactive wastes in porous rocks is one of the methods of dealing with waste used in Russia [1]. Reliability in localizing wastes in such stores is determined primarily by the geological parameters, which should guarantee isolation from the surface and aquifers. The wastes represent a complicated multicomponent system, which may influence geochemical equilibria and alter the conditions in an underground store [2, 3]. Therefore, long-time forecasting for the state of such a store is impossible unless one knows the main transformations occurring in the waste-groundwater-rock system [4, 5].There is evidence on the main parameters governing the trends and extents of physicochemical processes in the thermal and radiation fields from the behavior of major components of the wastes and the radionuclides, including sorption on rocks, coprecipitation on solids, and so on [6][7][8][9]. The stratal temperature can be monitored periodically in injection and observation boreholes. These data characterize individual points but do not give a general picture of the temperature pattern and do not define zones of maximum heating or the temperatures there. To forecast component states at various times after deposition, one needs to know the distributions of the heat and dose levels throughout the store.Descriptions have been given [10] of ways of determining energy release and radiation doses in deep storage. Methods have been given [11] for calculating temperature patterns in storing liquids with the addition of cement involving hydraulic stratal fracturing. That form differs considerably from the storage of liquid wastes because the cement converts them to the solid state, which radically alters heat transfer. Thermal calculations on liquid waste storage [4, 7, 12] have shown that agreement is obtained with experiment when one considers the detailed technology, which includes not only depositing the wastes but also the injection of preparatory and displacing solutions. That is fairly obvious because the supply of large amounts of inactive solutions substantially reduces the radionuclide concentrations, as the radionuclides are the sources of heat and affect the heat-transfer conditions. Unfortunately, those papers give no details of the models, and the software used remains unknown, so one cannot perform calculations for other storage conditions.The data show that one can characterize the state of an underground waste store from a model that includes the following: 1) description of deposition in the storage rock; 2) calculation of energy production and radiation dosage; 3) calculation of temperature pattern at various times; 4) a physicochemical model for the state of the components that includes sedimentation, sorption, coprecipitation, and so on; and 5) calculations on component migration underground.

A diffusion-kinetic model for the radiation-chemical degradation of oxalic acid and oxalates in aqueous solutions was developed. The model adequately describes published data on the formation of H 2 , H 2 O 2 , and CO 2 over wide ranges of acid concentrations and pH values.

The objective of this work was to study the physicochemical conditions and the microbiological composition of underground water in the second level of the Severnyi site at the Mining and Chemical Works and to clarify the possibility of biogenic gas production by formation microflora from macrocomponents of the wastes (nitrates and sulfate ions). Chemical analysis of samples of formation liquid from wells located in the dispersion zone of the wastes showed an increase in the content of dissolved carbonic acid, sodium nitrate, and nitrates of radionuclides and an increase of their concentrations in the sampling part. In all other samples, the contents of the main cations and anions were close to the background values. Microbiological investigations showed an increase in the number of microorganisms capable of forming gases from possible macrocomponents of the wastes and in the rate of sulfate reduction and methane generation processes within the propagation boundary of the wastes.One method of final removal of low-and medium-level wastes from the human environment is burial of the wastes in deep (200-500 m) water-bearing levels, isolated from lower and upper layers by clay interlayers which are impermeable to water. This method was first used in 1963, and more than 50·10 6 m 3 of liquid wastes with initial activity exceeding 4 billion Ci are now localized in deep repository formations [1]. Since the wastes removed contained, aside from radionuclides, inactive macrocomponents, deep repositories now contain a substantial quantity of toxic compounds -nitrates, acetates, and sulfates of alkali metals, iron, nickel, chromium, and so forth, which can contaminate underground and, possibly, surface ecosystems.Radioactive and inactive components of wastes in deep repositories interact with formation minerals and formation liquid and are heated by radiation-chemical and microbiological activity. The contribution of each of these processes depends on, first and foremost, the activity of the wastes. The action of medium-and high-level wastes on the formation and on the components of the wastes is determined by the energy released as result of the natural decay of the radionuclides. The ionizing radiation generated in the process and absorbed in the rock and formation liquid, containing macrocomponents, increases the temperature of the formation on the one hand and intensifies the purely chemical interaction of components with the