Civil Engineering ETDs

Publication Date

7-1-2016

Abstract

Salt formations may be used as repositories for long term isolation of nuclear waste. Excavating drifts in a subsurface salt formation produces granular salt spoils, which could be used as sealing material for boreholes and drifts. In drifts, the backfilled salt would conduct heat from the waste load to the host rock salt. The efficiency of heat dissipated from the backfill will depend on the thermal properties of the backfill. The results of this study show how these thermal properties evolve with the porosity of consolidating granular salt. Thermal properties and porosity of laboratory-consolidated salt and in situ partially consolidated salt were determined. The laboratory-consolidated salt was consolidated under a range of hydrostatic stresses with temperature and moisture conditions relevant to a potential repository environment. Additional measurements were made on an intact salt crystal and dilated polycrystalline host rock salt from the WIPP facility. Thermal properties in this study were measured using a transient plane source method at temperatures ranging from 50 ˚C to 250 ˚C. Porosity and grain density were measured using a porosimeter; granular salt porosities ranged from 0.005 to 0.33, with an average grain density of 2.161 g/cc. Thermal conductivity of granular salt was shown to be dependent on temperature as well as porosity; thermal conductivities decreased with increase in temperature and porosity. Thermal conductivity of dilated salt was lower than consolidated salt at comparable porosities. This is believed to be caused by the pervasive crack network present in the dilated salt which is expected to inhibit flow of heat more than the pores present in the consolidated salt. Specific heat of granular salt at lower temperatures decreased with increasing in porosity. At higher temperatures, porosity dependence was not apparent. The thermal conductivity and specific heat data were fit to empirical models and compared with results presented in literature. At comparable densities, the thermal conductivities of granular salt samples consolidated hydrostatically in this study were greater than those measured previously on samples formed by quasi-static pressing. Photomicrographs of thin sections suggested that the method of consolidation influenced the nature of the porosity of the samples (e.g., crack vs. pore), and this may account for the variation of measured thermal conductivities between the two consolidation methods.

Keywords

Thermal conductivity, Specific heat, Porosity, Granular salt, Consolidation

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Ng, Tang-Tat

Second Committee Member

Bauer, Stephen J

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