Experiment designs offered for discussion preliminary to an LLNL field scale validation experiment in the Yucca Mountain Exploratory Shaft Facility

It has been proposed (``Progress Report on Experiment Rationale for Validation of LLNL Models of Ground Water Behavior Near Nuclear Waste Canisters,`` Keller and Lowry, Dec. 7, 1988) that a heat generating spent fuel canister emplaced in unsaturated tuff, in a ventilated hole, will cause a net flux of water into the borehole during the heating cycle of the spent fuel. Accompanying this mass flux will be the formation of mineral deposits near the borehole wall as the water evaporates and leaves behind its dissolved solids. The net effect of this process upon the containment of radioactive wastes is a function of (1) where and how much solid material is deposited in the tuff matrix and cracks, and (2) the resultant effect on the medium flow characteristics. Experimental concepts described in this report are designed to quantify the magnitude and relative location of solid mineral deposit formation due to a heated and vented borehole environment. The most simple tests address matrix effects only; after the process is understood in the homogeneous matrix, fracture effects would be investigated. Three experiment concepts have been proposed. Each has unique advantages and allows investigation of specific aspects of the precipitate formation process. All could be done in reasonable time (less than a year) and none of them are extremely expensive (the most expensive is probably the structurally loaded block test). The calculational ability exists to analyze the ``real`` situation and each of the experiment designs, and produce a credible series of tests. None of the designs requires the acquisition of material property data beyond current capabilities. The tests could be extended, if our understanding is consistent with the data produced, to analyze fracture effects. 7 figs