Status report on the full-scale electric heater tests at the Hanford Near-Surface Test Facility

A Near-Surface Test Facility (NSTF) was constructed at the Hanford Site, in order to evaluate the thermomechanical response of basalt subjected to thermal loads. Two large-scale field tests using electric heaters to simulate nuclear waste canisters were started in July 1980, and are scheduled for completion during 1982. These tests are part of the program to examine the feasibility and provide the technology needed to design and construct a geological repository for the emplacement of high-level radioactive waste in basalt formations. In both tests, electric heaters were placed in vertical boreholes in the Pomona basalt flow in the floor of the NSTF. Full-Scale Heater Test No. 1 consists of a central heater canister surrounded by eight peripheral heaters. Heater power increased progressively during the test. Rock temperature at the borehole wall was in excess of 400/sup 0/C after 2 years of operation. Full-Scale Heater Test No. 2 consists of a single heater canister. Heater power increased progressively for 1-1/2 years followed by a 120-day cooldown period. The heater was restarted and power is currently being raised to the limits of the equipment. Rock temperature at the borehole wall just prior to cooldown was in excess of 400/sup 0/C. A visual more » comparison of a heater borehole wall was made from photographs taken prior to testing and during the cooldown. Rock temperature was in excess of 400/sup 0/C at the start of cooldown and had been in excess of 300/sup 0/C for about 300 days. No appreciable borehole decrepitation or thermally induced cracking was observed. « less