The Yucca Mountain Project

Ambient Testing: Drift Scale Seepage Test

These tests specifically address the conditions under which, and the rate at which, moisture could seep into niches (short drifts) in the repository region. Test goals are to determine the amount of seepage into drifts under a variety of episodic pulse events and to identify potential fast flow paths. Seepage into drifts controls the conditions in the ESF environment, the amount of water contacting waste, the rate of waste mobilization, and the transport of radionuclides within the drift and ultimately outside the repository region.

Ambient hydrologic conditions of the repository rock were measured in borehole clusters and niches located in the ESF. In addition, water containing dye was released in the boreholes to simulate an episodic pulse of natural water moving through the rock.

The seepage threshold tests were completed at Niche 3650 (3650m from the ESF North Portal). Moisture monitoring at Niche 3655 by the U.S. Geological Survey (USGS) will continue for one more year. The plan is to switch the testing and monitoring activities between these two niches in the near future.

Scientists will use the results to predict whether water percolating downward above a mined opening (waste emplacement drift or tunnel) will drip into the opening because of gravity, or migrate around the opening due to capillary retention (i.e., a drift acting as a barrier). It is important to determine whether a mined opening acts as a capillary barrier because the barrier may help isolate the waste by preventing water from entering the drift and coming into contact with waste packages.

Air-permeability tests in borehole clusters were performed to characterize the rock and to select borehole intervals for subsequent liquid-release tests. These liquid-release tests involved controlled release of water with dye tracers. Niches were then excavated and examined for the presence of dyed water to determine if and how far the dyed water had traveled.

Tests were repeated at various flow rates and injection volumes to further quantify seepage. Numerical modeling was used to design the tests and predict the outcome, and test results were used to further refine the models. After completion of the active testing phase, long-term monitoring of moisture was conducted, using sensors installed in the niches. Moisture measurements were used to calculate water flow and to quantify the interaction between fast flow paths and rock matrix.

For more information, please contact:
Joe Wang
Ph: 510-486-6753
or
Rob Trautz
Ph: 510-486-7954

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