Earth Sciences Division Berkeley Lab
Nuclear Waste Program
Annual Report 2000–2001
MOISTURE MONITORING ALONG A NONVENTILATED SECTION OF TUNNEL AT YUCCA MOUNTAIN Rohit Salve Contact: Rohit Salve, 510/486-6416, r_salve@lbl.gov
RESEARCH OBJECTIVES The monitoring study conducted in the Enhanced Characterization of the Repository Block (ECRB) East-West Cross Drift is designed to detect drips in sealed drift sections (Figure 1). The ECRB bulkhead sections are located in the area of the drift most likely to show seepage under ambient conditions. This monitoring effort is an integrated part of the field seepage testing and monitoring program at Yucca Mountain. The seepage studies, together with hydrological measurements in boreholes and benches, provide field measurements and data to be used for calibration and validation of unsaturated zone models related to seepage.
APPROACH To observe potential seepage, ventilation effects on the terminal section of the ECRB were minimized with the construction of two bulkheads. These bulkheads were installed in the ECRB in June 1999. A third bulkhead was installed in July 2000 to ameliorate (but not eliminate) the influence of some nearby heat sources on the tunnel conditions. Along the tunnel bore ECRB ESF
ERPs (Saturation Measurements) Existing Borings
TBM (Hot/Warm) X
Station 26+05 Station 26+00
X X
Station 25+03 Station 25+00
X Station 21+40 Station 20+00 Station 17+63 AT01-011
X Existing Relative Humidity/ Station 15+00 Temperature Measurements Additional Relative Humidity/ Temperature Measurements
Figure 1. Terminal 944 m of the ECRB showing the location of monitoring stations and three bulkheads
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(before and after the bulkhead) humidity, temperature, and barometric pressure are being measured at various stations to provide information on moisture dynamics along the ECRB. Additionally, psychrometer measurements of water potential are being made along the length of boreholes installed before and after the bulkhead.
ACCOMPLISHMENTS Six moisture-monitoring stations have been located before and after the bulkhead. Data from these stations, along with periodic observations from the nonventilated zone of the ECRB, have allowed for a better understanding of moisture dynamics in the ECRB. When the bulkhead doors were opened briefly in January 2001, the cross drift was observed to be dry from the first bulkhead (17+63 to 19+00 m). While there was evidence of water from 24+75 to 24+95 m (between the first and second bulkheads), most of it was concentrated between the second and third bulkheads. Temperature and relative humidity data from the three nonventilated zone (for the first four months in 2001) show that the temperature ranged between 24 and 33ÂşC, and the relative humidity ranged from ~80% to close to saturation.
SIGNIFICANCE OF FINDINGS Condensation observed in the nonventilated section in the ECRB could be from seepage or temperature fluctuations associated with air moving through the fault (or with the hot, moist air leaking through the third bulkhead). Our preliminary data suggest that the observed condensation could have been caused from warmer, moist air moving away from a heat source into cooler zones. Without eliminating the heat source, the cause of the observed condensation cannot be identified definitively.
ACKNOWLEDGMENTS This work was supported by the Director, Office of Civilian Radioactive Waste Management, U.S. Department of Energy, through Memorandum Purchase Order EA9013MC5X between Bechtel SAIC Company, LLC, and Berkeley Lab. The support is provided to Berkeley Lab through U.S. Department of Energy Contract No. DE-AC03-76SF00098.
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