A Unique Buffer Material For Nuclear Disposal Applications Essay
Three Bentonite properties, which makes it a unique buffer material for nuclear disposal applications are discussed in the following:
1) Thermal conductivity
Thermal conductivity is the rate at which heat can be transferred through a certain material. It is also expressed as the flux of heat, which flows per unit time through a unit distance with a temperature gradient of one degree per unit area. Thermal conductivity, like other tensor parameters, has different values in different directions. In SI units, thermal conductivity has the unit of watts per meter Kelvin (W/ (m*K)).
Each HLW (or spent fuel) disposal canister produces around 1000 to 2000 watts of heat during the decay processes. In order to reduce the heat related mineral alterations, the generated heat must be dissipated to the surrounding structure to limit the maximum temperature in the near-field. This will also limit pore-water overpressure and dilatation of the rock matrix. The maximum temperature in the Bentonite buffer is reached at an early phase of the repository’s lifetime, after around 50 years, when the residual heat from the waste is still high and the Bentonite is unsaturated or only partially saturated. At the interfaces between rock, Bentonite, and canister, the unsaturated Bentonite may leave small gaps through which heat can dissipate. The gaps are the required tolerances left from the installation of the canister in the Bentonite. The presence of gaps has a significant influence on…