Abstract

A strain-gauged proving-ring transducer was designed and deployed to measure small diametral displacements in 0.61-m diameter by 4.9-m deep boreholes in rock. The rock surrounding the boreholes was previously heated by storage of spent nuclear fuel assemblies and electrical resistance heaters. Borehole displacement measurements were made subsequent to removal of the spent fuel assemblies to document the rock response and to provide data for comparison with thermal-stress calculations. A transducer was designed to measure displacements in the range of 10 to 100 {mu}m, to function in a time-varying temperature regime of 30{sup 0} to 60{sup 0}C at a relative humidity of 100%, to be of low stiffness, and to be easily and quickly installed. The strain-gauged proving-ring technology provided a viable means of recording displacements in large (0.61 m) diameter boreholes in rock which are subjected to a time-varying thermal field. Design of a relatively simple transducer to measure borehole displacements was moderately successful. Inadquate environmental protection of the strain gauges resulted in 6 of 14 transducers failing with a mean life of 85 days. The surviving transducers performed adequately, based on comparisons of pretest and post-test calibration results. 5 refs., 3 figs., 1 tab.

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