A Review of the Swedish KBS-3 Plan for Final Storage of Spent Nuclear Fuel (1984) / Chapter Skim
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. In 1978 the Swedish proposal was described in a document entitled Handling and Final Storage of Unreprocessed Spent Nuclear Fuel and commonly referred to as KBS-2; a largely rewritten and considerably expanded version of the KBS-2 document, entitled Final Storage of Spent Nuclear Fuel, or KBS-3, is the subject of the present review.
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the long-term stability of copper canisters enclosed in a bentonite buffer and (2) the availability of deep geologic disposal sites with the necessary dimensions, stability, and groundwater properties for maintaining a benign canister environment and providing an effective secondary barrier to radionuclide migration.
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Like its predecessor KBS-2 subcommittee, the KBS-3 panel finds that the conclusions reached in the plan were warranted by the evidence submitted and is convinced that an adequate technical basis has been developed to provide reasonable assurance that radionuclides will not escape into the biosphere in unacceptable amounts from a repository located and constructed as specified by the KBS-3 plan. A few gaps and uncertainties in the evidence remain, despite the newer work, but the panel finds little reason to question the overall soundness of the KBS conclusion.
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Identification of suitable repository sites is made difficult by the need to extrapolate fracture patterns in bedrock from surface exposures to depths of 500 m, aided only by measurements in a few boreholes and by geophysical observations. Such extrapolation is to some degree necessarily speculative, but in KBS-3 the speculative aspect has been diminished by the use of additional deep boreholes and by improvements in geophysical techniques.
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Quantity, Movement, and Chemical Composition of Groundwater. Study of groundwater from boreholes at the newly explored repository sites has shown relations much like those found earlier at the sites described in KBS-2: wide variation in hydraulic conductivity from high values in zones of fracturing to very low values in relatively unfractured rock, and a general decrease in conductivity downward from the land surface.
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From page 6... ...
Details of the movement of released nuclides have been studied intensively during the past five years, especially with respect to oxidizing conditions that may be produced locally by radiolysis, enhancement of radionuclide movement by formation of complexes and colloids, and the modeling of groundwater flow through fractured rock. New models have been devised as alternatives to the commonly used hydrodynamic dispersion models for porous rocks, but the new models have actually been used only to a limited extent in estimating rates of radionuclide migration.
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From page 7... ...
The new work has been especially convincing in that much of it has involved field tests under repository conditions, a notable deficiency in the earlier studies. Some troublesome questions remain, for example those regarding the effectiveness of proposed shaft and tunnel seals, the validity of models for groundwater flow in fractured rock, and the adequacy of treatment of the many variables that influence retardation of radionuclides in their migration through granitic rock.
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