Initial results of tuff borehole sealing experiments
- Nuclear Regulatory Commission, Washington, DC (USA)
- Univ. of Arizona, Tucson (USA)
Laboratory and field experiments are in progress to determine the performance that can be expected of cementitious and of earthen (bentonite) seals when emplaced in welded tuff. Laboratory testing includes materials characterization testing radial permeameter testing of cementitious borehole plugs emplaced in welded tuff cylinders, flow testing of bentonite and of bentonite/crushed tuff plugs, axial strength of cementitious borehole plugs emplaced in welded tuff, and fracture grouting experiments. Experimental work is performed in Apache Leap tuff, a formation exposed in east-central Arizona. Mineralogical, chemical, hydrological and mechanical characterization shows reasonable similarity between the Apache Leap tuff and the Topopah Spring tuff, the proposed Yucca Mountain repository host formation. The main conclusion from the mechanical characterization testing is that the tested tuff, not unexpectedly, is an extremely heterogeneous rock, with highly variable properties. A second notable observation is the extremely low saturated hydraulic conductivity of intact welded tuff, notwithstanding its very high porosity. Mixtures of bentonite and crushed tuff show that samples containing 25 or 35 percent bentonite (by weight) have permeabilities of the same order of magnitude as similarly prepared and emplaced samples consisting of bentonite only. Permeability is noticeably pressure-dependent. Short-term bond strengths of cementitious seals emplaced in tuff cylinders are moderately high, in the range of 3 to 8 MPa, with considerable variability. Results indicate a marked decrease in strength with increasing plug (or borehole) diameter. A pronounced strength loss occurs at 90C, but not at 70C. 12 refs., 6 figs.
- Research Organization:
- American Nuclear Society (United States). Fuel Cycle and Waste Management Div.; American Society of Mechanical Engineers, New York, NY (United States); USDOE, Washington, DC (United States); Arizona Univ., Tucson, AZ (United States). Coll. of Engineering and Mines
- OSTI ID:
- 137779
- Report Number(s):
- CONF-900210--Vol.2
- Country of Publication:
- United States
- Language:
- English
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