Measuring Anisotropic Thermal Properties of Metagranite at Different Scales

The Swedish Nuclear Fuel and Waste Management Company has undertaken site characterization with the objective of sitting a geological repository for spent nuclear fuel. This includes measurements of the thermal properties of the rock and the in–situ temperature which are dimensioning parameters for canister spacing in order to meet the temperature criterion for the bentonite buffer. Consequently, the thermal properties also influence the size of the repository. Anisotropy in thermal conductivity is investigated since it may influence the peak temperature in the buffer. The thermal properties have been determined for different scales in the dominant foliated metagranite at the Forsmark site. The results shows that the anisotropic thermal properties are scale dependent. The anisotropy seems to be higher at a smaller scale than at larger scales. The geometric mean value given by the multi–probe method is similar to the TPS method, while the large–scale test yields a slightly higher value.