This paper presents a summary of results fxom the Single-Heater Test (SHT) at Yucca Moun- tain, Nevada. In the SHT, a horizontal, 5-m-long, line-heat source was used to heat a rock pillar for nine months. Moisture movement was monitored during and after heating using electrical-resistance tomography (ERT) and neutron-logging techniques. Results indicate drying in regions of the rock where temperature reached 60øC and above. The drying zone is asymmetric and is not centered on the heater, but has lobes ex- tending above and to the sides of the heater. Predicted temperatures agreed well with observations. A cold- trap effect was predicted, in the heater borehole, that efficiently transfers heat along the heater borehole to the excavation wall. A simple thermomechanical analysis of the SHT shows that shear zones predicted for vertical fractures coincide with regions of increased moisture content derived from ERT measurements.
The Single-Heater Test (SHT) was one phase of the field-scale thermal testing program of the Yucca Mountain Site Characterization Project (YMP). The purpose of the SHT was to study the coupled ther- mal-hydrologic-mechanical-chemical (THMC) be- havior of the Topopah Spring tuff, and the test was conducted in an alcove excavated off of the Explore- tory Studies Facility at Yucca Mountain, Nevada. The rock in this unit is a densely welded, non- lithophysal, ash flow tuff.
In this test a 5-m-long line-heat source was used to heat a rock pillar for approximately nine months. After the heater was turned off, the rock mass was monitored during the cool-down for another nine months, until May 28, 1997, when the test was ter- minated. Figure 1 shows the general layout of the SHT, including the boreholes that were drilled per- pendicular to the heater to monitor moisture move- ment along the approximate midplane of the test.
The SHT was a cooperative effort conducted by the YMP thermal test team, which includes partici- pants from four national laboratories (Lawrence Livermore National Laboratory, Lawrence Berkeley National Laboratory, Los Alamos National Labora- tory, and Sandia National Laboratories), the U.S. Geological Survey, and the YMP Management and Operating contractor. The THMC response of the rock mass to heating was monitored by several dif- ferent types of measurements, only a few of which are reported here. Thermal neutron logging and dec- tdcal-resistance tomography (ERT) were among the techniques used to monitor the rock's water satura- tion over time with the intent of estimating the movement of steam condensate out of the system. Section 2 of this paper presents a brief discussion of these methods and results and of the temperature history of the test. Section 3 presents a summary of thermohydrologic (TH) and thermomechanical (TM) simulations conducted for the SHT.