ABSTRACT:

This study involved the development and application of a methodology for evaluation of process models developed to capture the thermal-hydrological (TH) and thermal-hydrological-mechanical (THM) responses from the thermal tests associated with the Yucca Mountain Project (YMP). These thermal tests, which are referred to as the Drift Scale Test (DST), the Single Heater Test (SHT), and the Large Block Test (LBT), have different areal extents (ranging from 10 to 3000 m 2) and different electrical heater powers (ranging from 2.3 to 190 kW). All three thermal tests have insraiments and sensors that measure the T-H-M responses during heating/cooling periods that range from one to eight years. In this study, quantitative evaluation using statistical measures is emphasized. Results indicate the TH process model simulated the thermal response quite well; however, evaluating the same process models for simulation of the hydrological response is more difficult because, in part, of inherent uncertainties in the hydrological measurements. Similarly, the THM model is also affected by uncertainties but adequately replicated the mechanical response.

INTRODUCTION

The investigation of coupled processes, which includes thermal, hydrological, and mechanical (T-HM) responses, at the Yucca Mountain Project (YMP) relies, in part, on three in-situ thermal tests fielded in one of the three host rock units for the potential nuclear waste repository (CRWMS M&O 1999, CRWMS M&O 1998a, Wilder et al 1997). These thermal tests, which are referred to as the the Single Heater Test (SHT), the Drift Scale Test (DST), and the Large Block Test (LBT), have different areal extents (ranging from 10 to 3000 m 2) and different electrical heater powers (ranging from 2.3 to 190 kW). All three thermal tests have instruments and sensors that measure the T-H-M responses during heating/cooling periods that range from one to eight years (CRWMS M&O 1999, CRWMS M&O 1998b, and Wilder et al 1997). Specifically, resistance temperature detectors and thermocouples measured temperature, geophysical/neutron-logging techniques measured water saturations, and multi-point borehole extensometers measured displacements (CRWMS M&O 1997). Although chemical responses were also measured, they were not considered in this study. A key aspect of the YMP thermal testing program is the development and subsequent evaluation of process models, such as TH and THM models, that are used in the numerical simulation of the YMP thermal tests.

2. OBJECTIVE AND SCOPE

The objective of this study was to develop and to apply a methodology for evaluation of TH and THM models used to simulate the YMP thermal tests with emphases on the quantitative component. The scope of this study included two process models (TH and THM) and three thermal tests (DST, SHT, and LBT).

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