Underground Field Testing

"Never underestimate the importance of touching the rocks."   Anonymous



The work described below was conducted as part of my research with Lawrence Berkeley National Laboratory's Ambient Testing group.  This research was undertaken in support of the United States Department of Energy's Yucca Mountain Project, which is our nation's program to safely dispose of existing nuclear waste generated by civilian power production.  Currently, this spent nuclear fuel is stored in an ad-hoc fashion at dozens of locations around the country.  Like it or not, we have to find some way to deal with it, and the research described below is my contribution to that effort....



 
The Exploratory Studies Facility (ESF)
The Exploratory Studies Facility, or ESF, is the USDOE's underground laboratory at Yucca Mountain, Nevada, for in-situ studies related to the geologic disposal of high-level radioactive waste.  Eight kilometers long, 27 feet in diameter, and about 600 feet below the land surface at its deepest point, the ESF is a world-class testing and study facility. 

 
Thermal Testing Facility
Although I was an organizer of the original USDOE peer review group on thermal-hydrologic testing (THRET- Thermo-Hydrologic Review Evaluation Team) and an author on the original planning document, I have not been directly involved with the Thermal Testing Facility since.  However, it is such an impressive (and seldom seen) sight I thought people might be interested in a few pictures of it.  Some of the research I have been working on is related to the thermal testing, though, and as that research becomes more mature I will include it here.
The thermal testing area within the ESF is a one-of-a-kind facility, and a most impressive sight.  At a cost of many millions of dollars (none of which were provided by the tax payers) this area was constructed to study the complex thermal-hydrologic, chemical, and mechanical processes that result from burying 70,000 metric tons of spent nuclear fuel.  The photo to the right shows some of the data collection equipment associated with the test. 
To the left is a photo of a series of heaters within the test facility tunnel.  The heaters are the same size and shape of the proposed nuclear waste canisters, but are electrically heated to temperatures somewhat above the boiling point of water to simulate the effects of the waste heat that is a product of radioactive decay. 
Below is some of the underground testing I have been personnally involved in: the Fracture/Matrix Interaction Tests in Alcove 6.  There are indications that our present models of flow in fractured rock may overestimate the communication between fractures and matrix.  The Fracture/Matrix Interaction Tests were a series of in-situ liquid injection tests designed to gather data on this problem.  For more information on my research modeling flow in unsaturated, fractured rock, you can visit my web page: Modeling Flow in Unsaturated, Fractured Rock.
Fracture/Matrix Interaction Testing (Alcove 6)
Testing in the ESF is generally carried out in tunnels that extend from the main drift.  There are seven so-called "alcoves" extending from the main drift, as well as numerous smaller tunnels called "niches".  Within Alcove 6 is the test bed of the "Fracture/Matrix (F/M) Interaction Tests".  The F/M Interaction Tests were a series of studies in which water was injected in horizontal boreholes drilled into the wall of the alcove.  The water ran down through the fractures, and was captured in a series of trays located about one and a half meters below the injection borehole.  The photo on the left shows the test bed; the injection borehole is the black mark in the top of the photo, slightly left of center.  Plastic strips to reduce evaporative losses have been raised so that the collection trays are visible (near the bottom of the photo). 
The photo on the right shows myself and Rohit Salve of the Lawrence Berkeley National Laboratory's Ambient Testing group placing the trays in the collection slot cut into the rock wall under the injection borehole.  The slot was supported by specially designed and fabricated jacks made of I-beams, which also acted as guides for placing and removing the trays. 

The pre-test modeling shown below is an example of some of the work I did for test design.  You can click on the plots to get a better view, with readable text.  For more information on the test design modeling, see my paper "Numerical Modeling for Design of an In-Situ Liquid Injection Test" in the Proceedings of the International High-Level Radioactive Waste Management Conference, May, 2000.
 

Numerical Modeling Results: Sensitivity to Fracture Air Entry Pressure
The two plots shown here are examples of the pre-test modeling done to design the F/M Interaction Test.  In order to bound the size of the collection slot, it was necessary to know how wide the injection plume would be at the collection point.  Sensitivity testing of showed that the most important control on spreading was the strength of the fracture air-entry pressure.  On the left is a simulation with a "weak" capillary suction; on the right, a "strong" capillary suction.  On the basis of these simulations, the spread of the injection plume was projected to be between 0.3 and 2.0 meters. 

The images above were generated using a discrete fracture model.  The single fracture was populated with a statistically generated heterogeneous property distribution.  Each fracture grid block was associated with five homogeneous matrix grid blocks.  The final model grid contained about 25,000 grid blocks.
 

I'm on the lookout for a sharp graduate student or two, so if the above topics interest you give me a call (208/885-9259), or E-mail me at jfairley@uidaho.edu.
 
 
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Modeling in Unsaturated, Fractured Rock