I. M. Kosareva

Temperature Fields with Deep Burial of Liquid Radioactive Wastes: Simulation of Multistage Disposal

Newly developed computer codes were used to investigate the temporal and spatial variation of the temperature in a collector-stratum during multistage disposal of liquid wastes. It is shown that measurement of the temperature in the injection well after waste disposal has been completed can serve as an objective criterion for the thermal state of the stratum only if no technological operations are performed in the well. Comparing models with spherically and cylindrically symmetric arrangements of the wastes in the stratum shows that when calculating the temperature field at the active stage of the operation of the injection well both models give virtually identical results, while for calculations of the field after waste disposal has been completed the simplified spherically symmetrical model underestimates and the cylindrical model overestimates the maximum stratum temperature. 6 figures, 3 references.

Microbiological processes in the Severnyi deep disposal site for liquid radioactive wastes

Local monitoring of physicochemical, radiochemical, and microbiological parameters was performed in the deep horizons of the Severnyi site used for disposal of liquid radioactive waste (LRW). Analysis of the chemical and radiochemical composition of the wastes and formation fluid revealed that the boundary for migration of radionuclides lagged behind that for nonradioactive waste components (sodium nitrate) and tritium. The physicochemical and radiochemical conditions in deep horizons did not prevent microbial growth. The numbers of microorganisms (aerobic organotrophs, denitrifying, fermentative, sulfate-reducing, and methanogenic) were low, as were the rates of sulfate reduction and methanogenesis; they increased in the waste dispersion zone. The microorganisms from deep horizons were able to produce gases (CH4, CO2, N2, and H2S) from possible waste components. Denitrifying bacteria belonged to different Pseudomonas species and reduced nitrate to dinitrogen under the conditions of pH, salinity, temperature, and radioactivity found in the disposal site. These results suggest the need for control of microbiological processes in deep disposal site for liquid RW.

APPROACH TO SAFETY ASSESSMENT OF METHODS FOR HANDLING LIQUID RADIOACTIVE WASTES FROM NUCLEAR FUEL CYCLE ENTERPRISES

The application of the concept of deeply layered protection, which was developed for nuclear power plants, to modern methods for handling liquid radioactive wastes is examined. It is shown that this concept can be used successfully for assessing the safety status of different types of storage sites. It is concluded that it is desirable to develop for domestic nuclear fuel cycle objects a multilevel safety concept based on the principle of deeply layered protection and later to prepare on this basis the standardization documentation.

Substantiation of the Radiochemical Characteristics of Liquid Radioactive Wastes That Determine Safe Operation of Deep Waste Disposal Sites

The qualitative and quantitative radiochemical composition of liquid wastes is substantiated. This makes possible further safe operation of deep waste disposal sites at the Mining-Chemical Plant and the Siberian Chemical Plant. The toxicity and temperature in a formation with the wastes removed are used as the assessment criteria, satisfaction of which guarantees that the wastes will remain localized within the assigned boundaries of the waste-disposal formation site. It is concluded that the standard limit should be imposed on the specific activity of the long-lived group of radionuclides – 90Sr and 137Cs – rather than on the total specific activity of the wastes placed in deep disposal sites. For maximum specific activity of 90Sr and 137Cs of 37 GBq/dm3 and total specific activity not exceeding 185 GBq/dm3 for buried wastes with radionuclide composition characteristic of modern radiochemical production operations, it is impossible for potentially dangerous radiation and thermochemical processes to occur in the waste-disposal formation site. The recommended limit permits reducing substantially the volume of buried wastes and therefore the region over which the wastes propagate in the deep disposal site.