Earth Sciences Division
Research
Objectives
Nuclear Waste Program Thermal-Hydrological Modeling of the Drift Scale Test at Yucca Mountain, Nevada
Annual Report 1998-1999
along the heated drift wall to reach as high as 200째C.The heat output of the The Drift Scale Test (DST) is the canister and wing heaters can be second of the two in-situ heater tests adjusted over the full range to achieve being carried out in the underground these targets. Sumit Mukhopadhyay and Yvonne W. Tsang Exploratory Studies Facilities at Yucca Therm a l - hy d ro l o gical simu l a t i o n s Mountain, Nevada (the Single Heater of the DST are being performed with Contact: test, SHT, was the first). The primary the TOUGH2 simulator, an integrated Sumit Mukhopadhyay (510) 495-2440, smukhopadhyay@lbl.gov objective of the DST,as it was with the finite difference simulation program SHT, is to develop a better underfor nonisothermal flow of multicomstanding of the effect and influence of thermal-loading on the ponent, multiphase fluid in porous and fractured media. We use coupled thermal, mechanical, hy d ro l o gical and ch e m i c a l the EOS4 module, which supports the thermodynamics of non(TMHC) responses of the surrounding rock mass. isothermal two-phase flow of components air and water, with vapor-pressure-lowering capabilities. Approach The configurations, parameters, and initial and boundary conditions of the numerical model are designed to resemble the The primary difference between the DST, located in the midactual test conditions of the DST as closely as possible.The DST dle nonlithophysal unit of the Topopah Spring welded tuff of model domain encompasses three different stratigraphic layers Yucca Mountain, and the SHT is that of scale.Whereas the heatof Yucca Mountain; i.e., the upper lithophysal, the middle noning element of the SHT was only 5 m long and placed in a 9.6lithophysal, and the lower lithophysal units of the Topopah cm diameter borehole, the heated drift of the DST is 47.5 m long Spring fractured welded tuff.The heated drift itself is in the midand 5 m in diameter. Heating is provided by nine canister dle nonlithophysal unit. The material properties within each heaters,which are placed on the floor of the heated drift. In addilayer are assumed homogeneous. As far as feasible, the input tion, there are 25 wing heaters, placed perpendicular to the lonparameters of thermal and hydrological properties for the DST gitudinal axis of the heated drift, on each side of it. The wing numerical model have been derived from laboratory and field heaters are used to emulate the effects of adjacent heat-generatpre-test characterization data of the DST block. When site-specific measurements are not available,properties are derived from ing waste-storage drifts. Each wing heater is about 9.5 m long mountain-scale calibration to measured data from numerous sur(consisting of an inner and outer section, each about 4.5 m face-based boreholes. long), and the spacing between each wing heater is about 1.83 The results presented below are based on the hydrology propm. The canister heaters and wing heaters together have a heat erty sets, which are calibrated to an infiltration rate of 0.36 output of approximately 185 KW.The TMHC responses from the mm/yr. While different conDST are measured by ceptual models have been a p p rox i m a t e ly 3,500 senutilized for simulating the sors, which are placed in 147 TMHC responses from the bo reho l e s . Numerous va riDST, here we will present abl e s , i n cluding heater only the thre e - d i m e n s i o n a l power, temperature, thermal dual-permeability model, ex p a n s i o n , moisture and which assumes two separate m e chanical displacements are measured by these senc o n t i nua for the fra c t u re s sors, which are connected to and the matrix.The details of an automatic data collection the model can be found in system. Birkholzer and Tsang (1997, The heating phase in the 1998). DST started on Dec. 3, 1997. Results The planned duration for the heating and cooling phases The key pro c e s s e s is four years each. The heati nvo l ved in the therm a l ing phase has been planned hy d ro l o gical response of the to elevate temperatures of a unsaturated fractured tuff to substantial ro ck vo l u m e heat are as follows. As fo rm a( m o re than 10,000 cubic meters) above 100째C, while Figure 1. Fracture liquid saturation in a vertical plane (about 10 m from the west tion tempera t u re approaches 100oC around the heater, a l l owing the temperatures side of the heated drift) after 12 months of heating. 79