Modified transient plane source measurements of Olkiluoto migmatite

Finland is moving forward as the first country to solve the geological final disposal of spent nuclear fuel. Due to the temperature sensitive nature of the used disposal method, thermal design of the repository layout is necessary. This design process requires information of the thermal properties of the rock mass as confining parameters for modelling. As part of this process, modified transient plane source (MTPS) measurements of the thermal properties of Olkiluoto migmatite were carried out between 2019 and 2021. The MTPS method was used to measure simultaneously thermal conductivity and thermal effusivity. Additionally, density measurements were done, allowing the calculation of thermal diffusivity and specific heat capacity. The assumption of normally distributed data was tested using the Shapiro-Wilk test for normality and normal probability plots. Finally, the data were fitted with Gaussians using the maximum likelihood method.