FöRFATTARE
Larsson, Kristina

DATUM
2001-04-20

INSTITUTION
Väg- och vattenbyggnad / Bergmekanik

SAMMANFATTNING
The study of the rock mass at the planned nuclear waste storage at Äspö includes the effects of heating the rock mass due to placement of the waste. The waste will have a high temperature but will cool with time, which will increase the temperature of the surrounding rock to about 60°C. This will produce microcracking between the mineral grains due to differential thermal expansion. Microcracks decrease the strength of the rock mass, which can have serious consequences for a nuclear waste storage. It is therefore important to know the amount of thermal microcracking that is likely to occur at a given temperature increase. This can be estimated by knowing the coefficient of thermal expansion for the rock types present at the site.

The coefficient of thermal expansion can be determined in the laboratory by measuring the expansion of a sample over a temperature interval. This was done by using strain gauges glued to the samples and measuring the strain as the temperature was varied between room temperature and 70°C. The samples were immerged in water since the conditions at Äspö are saturated. The coefficient of thermal expansion (a) was then calculated by dividing the measured expansion with the temperature interval. The values of the axial coefficient achieved were compared to values found in the literature (Jumikis, 1983) and were found to be within the same order of magnitude. The value of the volumetric coefficient is often assumed to be equal to three times the value of the axial coefficient. This assumption was compared to measurements of the volumetric expansion and they were found to be in good agreement for both rock types.

ISSN 1402-1617 / ISRN LTU-EX--01/139--SE / NR 2001:139