Rock Instrumentation Problems Experienced during in Situ Heater Tests
A cooperative Swedish-American program is underway to investigate the suitability of granite as a deep underground storage medium for nuclear waste isolation. The experimental program, located in an inactive iron mine at Stripa, Sweden, includes three heater experiments to evaluate the thermomechanical response of a granite mass when subjected to the heat load of simulated canisters of high level nuclear waste. These experiments require the measurement of temperature, rock displacement and stress during one and a half years of heating and cool-down. The first heaters were turned on June 1, 1978 and the last heater turned off September 26, 1979. Rock temperatures over 300°C have been measured and the mechanical response of the rock has been measured at temperatures to 150°C. Measured heater skin temperatures have approached 500°C. Few of the available instruments are designed to meet the accuracy and reliability requirements at the elevated temperatures encountered in this type of experiment. Therefore, available instruments have been modified and tested; and calibration techniques have been developed in an attempt to meet more strigent requirements. The modified instruments have produced a wealth of valuable data at Stripa in spite of some specific problems discussed here (1).
KeywordsHeater Experiment Thermocouple Wire Lawrence Berkeley Laboratory High Level Nuclear Waste Stainless Steel Sheath
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