[1] A cross-hole tracer test involving the simultaneous injection of two nonsorbing solute tracers with different diffusion coefficients (bromide and pentafluorobenzoate) and a weakly sorbing solute tracer (lithium ion) was conducted in a fractured granite near an underground nuclear test cavity in central Nevada. The test was conducted to (1) test a conceptual radionuclide transport model for the site and (2) obtain transport parameter estimates for predictive modeling. The differences between the responses of the two nonsorbing tracers (when normalized to injection masses) are consistent with a dualporosity transport system in which matrix diffusion is occurring. The large concentration attenuation of the sorbing tracer relative to the nonsorbing tracers suggests that diffusion occurs primarily into matrix pores, not simply into stagnant water within the fractures. The relative responses of the tracers at late times suggest that the diffusion-accessible matrix pore volume is possibly limited to only half the total volume of the flow system, implying that the effective retardation factor due to matrix diffusion may be as small as 1.5 for nonsorbing solutes in the system. The lower end of the range of possible sorption K d values deduced from the lithium response is greater than the upper 95% confidence bound of K d values measured in laboratory sorption tests using crushed granite from the site. This result suggests that the practice of using laboratory sorption data in field-scale transport predictions of cation-exchanging radionuclides, such as 137 Cs + and 90 Sr ++ , should be conservative for the SHOAL site.

Abstract. The objective of this research was to investigate the effects of matrix diffusion on solute transport in fractured volcanic tuff. Two tuff cores were studied, one with a matrix porosity of 0.27 and the other with a porosity of 0.14. The matrix permeabilities of the cores were 4.7 x 10 -•5 and 7.8 x 10 -•9 m 2, 5 and 9 orders of magnitude less than the respective fracture permeabilities. This suggested that the cores could be modeled as dualporosity systems with no flow in the matrix but significant solute storage capacity. Two types of tracer tests were conducted in each fractured core: (1) iodide was injected in separate experiments at different flow rates and (2) two tracers of different matrix diffusion coefficients (bromide and pentafluorobenzoate (PFBA)) were injected in another test. A difference in the maximum concentrations of the solutes and the extended tailing of the breakthrough curves were assumed to be indicative of diffusive mass transfer between the fracture and the porous matrix of the cores. Interpreting the results from both methods allowed the identification of matrix diffusion and dispersion effects within the fracture by simultaneously fitting the data sets (with known constraints) using a relatively simple conceptual model. Estimates of mass transfer coefficients for the fractured cores were also obtained. IntroductionBecause solute transport is controlled by both the physical nature of the flow system and the characteristics of the solutes (velocity, dispersivity, water saturation, sorption behavior, and diffusion coefficient), it is often difficult to determine the im- Separate samples of each core were used for matrix diffusion coefficient, porosity, and permeability measurements. These experiments provided independent estimates of the matrix diffusion coefficients of the different solutes used in the fractured core experiments.The dual-porosity conceptual model accurately described solute transport through the fractured cores and captured the importance of fracture/matrix interactions. The solute breakthrough curves follow a -1.5 slope in log space, which is probably due to diffusive mass transfer between the fracture and the surrounding porous matrix. However, the independent matrix diffusion coefficient measurements for Br-and PFBA in the same rock types were smaller than those calculated from 3547

No abstract

The gas permeabilities of more than 20 polymers were measured using pure and mixed gas techniques. The motivation was to determine potential materials that could be used to protect hydrogen getter particles from poisons while permitting sufficient hydrogen rates to enable the getters use in TRUPACT types of containers. A rate of five barrers or larger is needed. Of the materials screened in the pure gas tests, more than 15 qualified. Nine materials qualified in the mixed gas tests, but of the nine only three had high CCl 4 rejection rates and four others would greatly reduce the transport of the CCl 4 .TRUPACT-II to minimize the potential for loss of containment during transport (1). This limit is set at the lower explosive limit of 5 vol % of hydrogen in air. Hydrogen gas generation and accumulation are the result of alpha radiolysis of hydrogenous waste and packaging materials coupled within waste packaging configurations. One method to prevent hydrogen buildup is to employ a hydrogen getter within the containers.

No abstract

No abstract