Air spaces in a deep geologic repository for nuclear high level waste will have an important effect on the long-term performance of the waste package. The important temperature effects of an annular air gap surrounding a high level waste canister are determined through 3-D numerical modeling. Air gap properties and parameters specifically analyzed and presented are the air gap size, surfaces emissivity, presence of a sleeve, and initial thermal power generation rate; particular emphasis was placed on determining the effect of these variables have on the canister surface temperature. Finally a discussion based on modeling results is presented which specifically relates the results to NRC regulatory considerations.

Thermal conductivity, thermal expansion, and specific heat measurements have been made on a number of specimens. The specific heat measurements were made by differential scanning calorimetry and the results showed that the specific heats of both clean rocksalt samples and of dirty samples with less than or equal to 7% insoluble impurities were essentially identical to the published specific heat for pure NaCl. In the thermal expansion measurements, two distinct groups of samples were identified. The first group had average expansion coefficients in the temperature range 300 to 700/sup 0/K close to that reported for pure NaCl. All the samples in this group were composed predominantly of halite, with only small amounts of other minerals or materials present. A second group of samples had expansion coefficients only approx. 0.3 to 0.5 that of NaCl. The samples in this group were composed largely of polyhalite, anhydrite, or siltstone. The measurements first reported by Acton on the thermal conductivity of samples taken from a borehole at the site of the proposed nuclear waste isolation pilot plant (WIPP) near Carlsbad, NM, have been extended to include additional samples and higher temperature measurements. This is not believed to be the result of the onset …