Laboratory r.1easurements of radon fluxes and radon concentration profiles were conducted to characterize the effectiveness of multilayer cover systems for uranium tailings. The cover systems utilized soil and clay materials from proposed disposal sites for the Vitro, Durango, Shiprock, Grand Junction and Riverton tailings piles. Measured radon fluxes were in reasonable agreement with values predicted by multilayer diffusion theory. Results obtained by using air-filled porosities in the diffusion calculations were similar to those obtained by using total porosities. r~easured diffusion coefficients were a better basis for predicting radon fluxes than were correlations of diffusion coefficient with moisture or with air porosity. Radon concentration profiles were also fitted by equations for multilayer diffusion in the air-filled space. Layer-order effects in the multilayer cover systems were examined and estimated to amount to 10 to 20 percent for the systems tested. Quality control measurements in support of the multilayer diffusion tests indicated that moisture absorption was not a significant problem in radon flux sampling with charcoal canisters, but that the geometry of the sampler was critical. The geometric design of flux-can samplers was also shown to be important. Enhanced radon diffusion along the walls of the test columns was examined and was found to be insignificant except when the columns had been physically disturbed. Additional moisture injected into two test columns decreased the radon flux, as expected, but appeared to migrate into surrounding materials or to be lost by evaporation. Control of moisture content and compaction in the test columns appeared to be the critical item affecting the accuracies of the experiments.
Field tests of earthen materials conducted cover were on tailings 6 piles at Salt Lake City and Mexican Hat, Utah and at Grand Junction, I Colorado. The cover tests were contained in 1.2 m (4 ft) diameter columns I buried in the tailings, and involved local soils of 2.4-3.7 m (8-12 ft) thickness. The performancesof the covers were evaluated with respect to l their reduction of the radon fluxes escaping from the bare tailings. A radon diffusioncoefficientof 0.036 cm2/s was obtained for the 12 ft cover I at Mexican Hat, which reduced the radon flux from 99 to 10 pCi/m2s. At i Grand Junction,diffusion coefficientsof 0.024 and 0.029 were respectively obtained for 8 and 12 ft covers,which respectivelyreduced radon fluxes to l 250 and 100 pCi/m2s. The higher fluxes resulted from the much higher 2000 pCi/m2s source flux at this site. At Salt Lake City, the measured
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