Nuclide transport

As a first approximation it can be assumed that the water and nuclide transport would take place only in major fractures of the rock and also that the nuclide retention is merely a surface reaction limited by the exposed fracture surface area. 

Allard, B., Kipatsi, H., Torstenfelt, B. and Rydberg, J., "Nuclide Transport by Groundwater in Swedish Bedrock", Symp. on Radioactive Waste Management, Boston, Nov. 28 - Dec. 1, 1978, in press... 

Phenomena such as nuclide transport by particles or nuclide transport in colloidal form will interfere with a kinetic approach to predicting nuclide migration. The results indicate that the measurement of kinetic parameters may be as important to understanding the migration of a nuclide through a geologic media as the measurement of the equilibrium-sorption value (Kj). 

The liquid waste is stored for at least 6 y prior to solidification to reduce the decay heat (Fig. 16.8) by a factor of 10 or more. The first U.S. military fuel reprocessing wastes were stored as neutralized waste in mild steel tanks at the Hanford reservation in eastern Washington. These steel-lined, reinforced-concrete tanks were 500,000-1,000,000 gal in capacity with provisions for removal of waste heat and radiolysis products. Corrosion of several tanks occurred with the release of waste. Fortunately, the soil around these tanks retarded nuclide transport. A better (and more expensive) design for storage tanks was implemented at the Savannah River site in South Carolina consisting of a second steel tank inside of a Hanford-style tank. The storage of acid waste in these tanks has not encountered the corrosion problems seen with the Hanford tanks. 

Allard B, Kipatsi H, Torstenfelt B, et al. 1979. Nuclide transport by groundwater in Swedish bedrock. Mater Res Soc Symp Proc 403-410. 

Fig. 1.6 isothermal chromatography of short-lived cyclotron produced nuclides transported by helium (cluster) jet [23]. 

By simulating the physicochemical characteristics of a waterway system, the flume can be used effectively in determining the relationships of flow conditions to nuclide transport, concentration of nuclides by plants and bottom sediment, and distribution of individual nuclide species between aqueous solution and plants and between aqueous solution and sediments. Measurement of responses of the system to stress can aid in the development of, or verification of, prediction models for oxygen balance. 

IMPACT OF TEMPERATURE INCREASE ON NUCLIDE TRANSPORT IN CRYSTALLINE ROCK ON THE NEAR FIELD SCALE... 

Moreno, L., and Neretnieks, I., 1993. Flow and nuclide transport in fractured media The importance of the flow-wetted surface. Journal of Contaminant Hydrology, 13 49-71. Neretnieks, I., 1980. Diffusion in the rock matrix An important factor in radionuclide retention. Journal of Geophysical Research, 85 4379-4397. 

To estimate the influence of partial coupling of the processes the simulation was also performed using T-H and C-H models. Figure 4 shows evolution in time of vertical positions of TDS and activity plumes mass centers. This figure shows the different influences of the modeled processes on the TDS and activity. These plumes are stratified in the vertical direction due to the influence of thermal viscosity effects on nuclides transport and influence of density-concentration relation on TDS transport. 

The most likely way radionuclides can migrate from the repository to the biosphere is by groundwater transport. For that reason, special emphasis must be placed on the hydrogeological and geochemical properties of the host medium to restrict nuclide transport by groundwater. The possibility of tectonic, seismic and other disturbances which can create new paths for the transport of radionuclides shall also be carehilly evaluated. 

Both dynamic melting and equilibrium transport melting require that the porosity when two nuclides are fractionated from one another is similar to the size of the larger of the partition coefficients for the two nuclides. Given the low values of the experimental determinations of Du and Dxh, the porosities required to explain the observational data in these models are generally less than 0.5% and often times closer to 0.1%. Such low porosity estimates have been criticized based on physical grounds given the low estimated mantle permeability derived from the extent of melt connection observed in experiments (Paul 2001). 

In contrast to the full equilibrium transport model, melt could be incrementally removed from the melting solid and isolated into channels for melt ascent. This model is the disequilibrium transport model of Spiegelman and Elliott (1993). Instead of substituting Equation (A7) in for Cs, the problem becomes one of separately keeping track of the concentrations of parent and daughter nuclides in the solid and the fluid. In this case, assuming steady state, two equations are used to account for the daughter nuclide ... 

Equation (A9) accounts for the change in the amount of daughter within the solid while Equation (A 10) accounts for that in the fluid. The transfer of the nuclide from the solid to the fluid phase is governed by the first term on the right side of both equations. Note that in this formulation, as given in Spiegelman and Elliott (1993), the time of melt transport is accounted for and depends on the physically based transport velocity. Like Equation (A8), both equations can be solved simultaneously by numerical integration or more sophisticated numerical method. 

Processes controlling nuclide distributions. The general equations for onedimensional advective transport along a groundwater flow path of groundwater constituents, and the incorporation of water/rock interactions, are given in such texts as Freeze and Cherry (1979). The equations can be applied to the distribution in groundwater of each isotope I with a molar concentration Iw and parent with Pw to obtain... 

Modeling of the transport of the long-lived nuclides, especially U, require knowledge of the input at the water table as a boundary condition for aquifer profiles. There are few studies of the characteristics of radionuclides in vadose zone waters or at the water table. Significant inputs are likely to occur to the aquifer due to elevated rates of weathering in soils, and this is likely to be dependent upon climatic parameters and has varied with time. Soils may also be a source of colloids and so provide an important control on colloidal transport near recharge regions. 

Porcelli D, Andersson PS, Baskaran M, Wasserburg GJ (2001) Transport of U- and Th-series nuclides in a Baltic Shield watershed and the Baltic Sea. Geochim Cosmochim Acta 65 2439-2459 Puls RW, Powell RM (1992) Acquisition of representative ground-water quality samples for metals. Ground Water Monitor Remediat 12 167-176... 

And the ratio of the nuclides in the net horizontally transported portion is assumed to equal that observed in the water column ... 

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