The Waste Isolation Pilot Plant A Potential Solution for the Disposal of Transuranic Waste (1996) / Chapter Skim
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6 NON-SALADO HYDROLOGY
6 NON-SALADO HYDROLOGY
Pages 65-76
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From page 65... ...
assumed a twodimensional, steady state, horizontal flow of ground water in the Culebra Dolomite, with simple parameterizations of both chemical and physical retardation mechanisms to describe solute transport. The discussion below outlines the main shortcomings of the 1992 PA models and analysis.
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From page 66... ...
results. For example, the PA models allow chemical retardation or matrix diffusion to attenuate radionuclides abler release to the Culebra.
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From page 67... ...
Conceptual Errors If the conceptual models upon which the PA models are based are in error, then all of the complementary cumulative distribution functions (CCDFs; see Chapter 2 and Appendix B) and risk assessments derived from the PA also may be in error.
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From page 68... ...
The SECO codes have not yet been subject to extensive benchmarking or international comparisons with other widely accepted codes, such as have been performed for other codes under the recent International Hydrologic Code Intercomparison Project (HYDROCOIN) and the International Project to Study Validation of Geosphere Transport Models (INTRAVAL; Swedish Nuclear Power Tnspectorate, 1987, 1990~.
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From page 69... ...
Although the Ethology at WIPP is different from that at the Swedish sites, these approaches have worked In other sedimentary rock basins, and the committee believes that they should be applied in the characterization of the WIPP site. An approach to fracture definition that is potentially more definitive, but also significantly more expensive, would involve drilling of slanted or even honzontal boreholes.
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From page 70... ...
This Tolled appear to eliminate the potential for future human exposure, which is an underlying basis for the overall concerns about radionuclide releases. The non-potable saline character of the ground water in the Culebra will greatly reduce the exposure hazard even though the radionuclides released to the accessible environment may exceed the limits required for compliance in 40 CFR 191.
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From page 71... ...
Some of the 1992 PA simulations of solute transport have allowed physical and/or chemical retardation, as would be denved from matrix diffusion and chemical sorption, respectively. To date, however, no reliable and representative field measurements of the
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From page 72... ...
Confidence in PA Analysis of Physical Retardation If PA results indicate that repository compliance with EPA standards depends strongly on matrix diffusion, more reliable field evidence to support the assumed range of coefficients should be obtained. In this case, field tests should be completed at several different locations In the vicinity of the WIPP site because of the spatial variability In the properties of the system.
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From page 73... ...
Because the specific solutes of interest here, such as plutonium and americium, cannot be used in tracer tests, reasonably appropriate surrogate tracers must be used, or field evidence of sorptive behavior must be ascertained from analysis of previous accidental releases elsewhere. As hypothesized for flow parameters for the Culebra Dolomite, a correlation may also exist between Ka (or Rf)
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From page 74... ...
, the HI scenario assumes that fixture Knifing wail facilitate upward leakage of brine Tom the repository through a borehole, thereby permitting radionuclides to be released into an overlying geologic formation through which lateral migration offers a possible pathway for release of radionuclides to the accessible environment. If releases exceed regulatory limits, then a predicted rate of transport in the regional ground-water system above the Salado Formation becomes a critical factor in estimating cumulative releases.
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From page 75... ...
as a single parameter (i.e., an effective retardation factory, as was done in the 1992 PA, has a very weak scientific basis. If the PA assumes that chemical retardation occurs in the Culebra, then supporting evidence from the field environment should be available before any predictions based on that assumption are accepted.
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From page 76... ...
To the extent that long ground-water travel times and significant physical and chemical retardation are necessary to ensure adequate isolation of radionuclides from the accessible environment, characterization of the site is correspondingly necessary to address these problems. KNAPP: A Potential Solution for the Disposal of Transuranic Waste Predicting regional ground-water flow and Most repository sites worldwide are located in rock radionuclide transport behavior with the reliability and that is part of an active regional ground-water regime.
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