An in situ borehole heater test was carried out in an underground research tunnel, which is for the validation of high-level radioactive waste disposal system suggested in Korea. For the test at a shallow depth in granite, the thermal and mechanical properties of rock were measured at different conditions. During the test, the heater temperature was increased to 90°C to simulate the thermo-mechanical behavior of crystalline rock under normal underground repository conditions. For simulating an abnormal over heating condition, the heater temperature was increased to 115°C at the end of the test. The air, wall and rock temperatures were measured over a period of several years. The peak temperatures at the observation holes located at 0.3m and 0.6m from the heater hole were approximately 50°C and 37°C, respectively. From the temperature measurements, it was possible to observe thee influence of rock joints and the influence of heat convection through the tunnel wall.

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