A New Approach to the Selection of Materials for Engineered Barriers and Appropriate Host Rocks for High Level Waste Dis
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A NEW APPROACH TO THE SELECTION OF MATERIALS FOR ENGINEERED BARRIERS AND APPROPRIATE HOST ROCKS FOR HIGH LEVEL WASTE DISPOSAL OMELIANENKO B.I., NIKONOV B.S., RYZHOV B.I., SHIKINA N.D., YUDINTSEV S.V. Institute of Geology of Ore Deposits, Russian Academy of Sciences Staromonetny, 35, 109017 Moscow, Russia. ABSTRACT Sorptive properties of weathered dunites, gabbro-diabases and basic volcanic rocks for Sr and Cs were studied. The results show that the sorptive capacities of these rocks are equivalent to or, in some cases, superior to industrial sorptive materials. Results of a uranium distribution study by fission-track radiography suggest that material from weathered basic rocks is characterized by high sorptive properties for uranium also. One can assume that other radionuclides of the transuranic group will be intensely sorbed by the residuum of weathered basic rocks. Low-temperature hydrothermal transformation leads to sealing fissures of the basic rocks with highly sorptive minerals, for example, smectite, chlorite, serpentine, talc, zeolite, hydroxides of Fe, Ti, Mn. The process results in contemporaneous decreasing hydraulic conductivity and increasing sorptive capacity of the rocks. HLW disposal at the radiochemical plant "Mayak" is expected to be produced in deep wells situated in basaltic rocks. The safety of disposal is based on high sorptive properties of the crust of weathering and protective capacities of volcanic rocks. This method is not expensive and may allow the disposal of HLW in the near future. INTRODUCTION For the succesful solution of the problem of safe high level waste (HLW) disposal in Russia it is necessary to take into account such factors as the existence of a great volume of HLW accumulated, the large size and the variety of geological conditions of the country and its very difficult economical situation. So the most efficient method of HLW disposal consists of the maximum usage of natural inexpensive minerals for engineered barrier construction and the protective capacities of host rocks. The principal requirements for employing natural minerals as buffer and backfill material in HLW repositories are high sorptive properties, low water permeability, relatively high thermal conductivity, thermo and radio stability. The major task of the buffer is to prevent the leakage of radionuclides from HLW to groundwater. In most waste isolation technologies montmorillonite with some addition of quartz sand is considered for use as a buffer material. Montmorillonite's advantages are its low water permeability and high sorptive characteristics with regard to Cs and Sr. At the same time, the results of radiogeochemical investigations indicate that montmorillonite is not an optimal sorptive barrier. Montmorillonite is a less effective material for buffer construction than many other minerals, especially those formed in the process of weathering of basic igneous rocks. Weathering products of basic rocks satisfy all of above properties. HLW consists of a wide spectrum of radionuclides that are characteri
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