Thermal properties and experiment at Äspö HRL

Kapitel i bok, 2017

The underground hard rock laboratory at Äspö (Äspö HRL), situated north of Oskarshamn, Sweden, is where much of the research about the final repository for spent nuclear fuel is taking place. The Äspö HRL is a unique research facility situated 450 meters underground. One part of the investigations at Äspö HRL, and the adjacent Simpevarp and Laxemar areas, has focused on thermal transport properties in the rock. The thermal properties of the rock have large influence on the thermal design of an underground repository for spent fuel. Temperature requirements on the canister or the surrounding buffer influence the distances between canisters and tunnels. The relevant scale for the thermal processes is of importance. This chapter discusses influences on thermal transport properties in crystalline rock with respect of e.g. scale, mineral composition and anisotropy. Primarily these processes are discussed according to methods for determination of thermal conductivity, from laboratory measurements to large scale experiments. The chapter also discusses indirect methods that make it possible to calculate the thermal conductivity from mineral composition and from the density log, including the theoretical base. Results on thermal conductivity and heat capacity from common rock types are reported. The development of prediction methods in different scales are exemplified with large scale thermal response test and inverse modeling at the prototype repository. Finally the strategy is outlined for the site descriptive thermal modeling in the Swedish site investigation program for nuclear waste disposal.