Electrical resistivity monitoring of the single heater test in Yucca Mountain FY98 -- 1st quarter results Page: 3 of 13
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Electrical Resistivity
Monitoring of the Single Heater Test
in Yucca Mountain, FY 98 - 1st Quarter Results
A. Ramirez, W. Daily
Lawrence Livermore National Laboratory
Abstract: Of the several thermal, mechanical and hydrological measurements being used to
monitor the rockmass response in the Single Heater Test, electrical resistance tomography
(ERT) is being used to monitor the movement of liquid water with a special interest in the
movement of condensate out of the system. Images of resistivity change were calculated using
data collected before, during and after the heating episode. This report will concentrate on the
results obtained after heating ceased; previous reports discuss the results obtained during the
heating phase. The changes recovered show a region of increasing resistivity approximately
centered around the heater as the rock mass cooled. The size of this region grows with time and
the resistivity increases become stronger. The increases in resistivity are caused by both
temperature and saturation changes. The Waxman Smits model has been used to calculate rock
saturation after accounting for temperature effects. The saturation estimates suggest that
during the heating phase, a region of drying forms around the heater. During the cooling phase,
the dry region has remained relatively stable. Wetter rock regions which developed below the
heater during the heating phase, are slowly becoming smaller in size during the cooling phase. The
last set of images indicate that some rewetting of the dry zone may be occurring. The accuracy
of the saturation estimates depends on several factors that are only partly understood.
Introduction
The Single Heater Test (SHT) is one of the in situ thermal tests being conducted in the
exploratory studies facility (ESF) in Yucca Mountain to enhance the understanding of the coupled
processes. The primary objective of the SHT is to investigate the thermal-mechanical responses
of the Topopah Spring tuff in Yucca Mountain.
This paper describes electrical resistance tomography (ERT) surveys made during the SHT in
order to map the changes in moisture content caused by heating. Of particular interest, is the
formation and movement of condensate within the fractured rock mass. In this report, we
concentrate on the results observed during the first quarter of FY 98. In this quarter, monitoring
of the cooling phase continues.
Electrical Resistance Tomography
Electrical resistance tomography (ERT) is a geophysical imaging technique which can be used to
map subsurface resistivity. Rock mass heating creates temperature and liquid saturation
changes which result in electrical resistivity changes that are readily measured. The ERT1
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Daily, A. R. W. Electrical resistivity monitoring of the single heater test in Yucca Mountain FY98 -- 1st quarter results, report, January 13, 1997; California. (https://digital.library.unt.edu/ark:/67531/metadc688958/m1/3/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.