DEVELOPMENT OF THE PERFORMANCE CONFIRMATION PROGRAM AT YUCCA MOUNTAIN, NEVADA

ABSTRACT The Yucca Mountain Performance Confirmation program consists of tests, monitoring activities, experiments, and analyses to evaluate the adequacy of assumptions, data, and analyses that form the basis of the conceptual and numerical models of flow and transport associated with a proposed radioactive waste repository at Yucca Mountain, Nevada. The Performance Confirmation program uses an eight-stage risk-informed, performance-based approach. Selection of the Performance Confirmation activities (a parameter and a test method) for inclusion in the Performance Confirmation program was done using a risk-informed performance-based decision analysis. The result of this analysis and review was a Performance Confirmation base portfolio that consists of 20 activities. The 20 Performance Confirmation activities include geologic, hydrologic, and constructiodengineering testing. Several of the activities were initiated during site characterization and are ongoing. Others activities will commence during construction andor post emplacement and will continue until repository closure

Use of thermal data to estimate infiltration, Yucca Mountain, Nevada

Temperature and pressure monitoring in a vertical borehole in Pagany Wash, Yucca Mountain, Nevada, measured disruptions of the natural gradients associated with the February, 1998, El Nino precipitation events. The temperature and pressure disruptions indicated infiltration and percolation through the 12.1 m of Pagany Wash alluvium and deep percolation to greater than 35.2 m into the Yucca Mountain Tuff

Simulating the Evolution of Fluid Underpressures in the Great Plains, by Incorporation of Tectonic Uplift and Tilting, with a Groundwater Flow Model

Underpressures (subhydrostatic heads) in the Paleozoic units underlying the Great Plains of North America are a consequence of Cenozoic uplift of the area. Based on tectonostratigraphic data, we have developed a cumulative uplift history with superimposed periods of deposition and erosion for the Great Plains for the period from 40 Ma to the present. Uplift, deposition, and erosion on an 800 km geologic cross-section extending from northeast Colorado to eastern Kansas is represented in nine time-stepped geohydrologic models. Sequential solution of the two-dimensional diffusion equation reveals the evolution of hydraulic head and underpressure in a changing structural environment after 40 Ma, culminating in an approximate match with the measured present-day values. The modeled and measured hydraulic head values indicate that underpressures increase to the west. The 2 to 0 Ma model indicates that the present-day hydraulic head values of the Paleozoic units have not reached steady state. This result is significant because it indicates that present-day hydraulic heads are not at equilibrium, and underpressures will increase in the future. The pattern uncovered by the series of nine MODFLOW models is of increased underpressures with time. Overall, the models indicate that tectonic uplift explains the development of underpressures in the Great Plains

Air-injection testing in vertical boreholes in welded and nonwelded tuff, Yucca Mountain, Nevada /

Shipping list no.: 97-0179-P."Interagency agreement DE-AI08-92NV10874."Includes bibliographical references (p. 32-33).Mode of access: Internet

Pneumatic testing in 45-degree-inclined boreholes in ash-flow tuff near Superior, Arizona /

"Interagency Agreement DE-Al08-92NV10874."Shipping list no.: 96-0040-P.Includes bibliographical references (p. 26-27).Mode of access: Internet

Results from air-injection and tracer testing in the upper Tiva Canyon, Bow Ridge Fault, and upper Paintbrush contact alcoves of the Exploratory Studies Facility, August 1994 through July 1996, Yucca Mountain, Nevada /

Shipping list no.: 98-0293-P.Includes bibliographical references (p. 28).Mode of access: Internet

Use of temperature, pressure, and water potential data to estimate infiltration and monitor percolation in Pagany Wash associated with the winter of 1997-98 El Niño precipitation, Yucca Mountain, Nevada /

Includes bibliographical references (p. 24-25).Interagency Agreement.Mode of access: Internet

Results from geothermal logging, air and core-water chemistry sampling, air-injection testing, and tracer testing in the northern Ghost Dance Fault, Yucca Mountain, Nevada, November 1996 to August 1998 /

Shipping list no.: 2000-0235-P.Includes bibliographical references (p. 46-47).Mode of access: Internet