The Waste Isolation Pilot Plant A Potential Solution for the Disposal of Transuranic Waste (1996) / Chapter Skim
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2 REGULATORY COMPLIANCE AND REPOSITORY PERFORMANCE
2 REGULATORY COMPLIANCE AND REPOSITORY PERFORMANCE
Pages 15-36
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From page 15... ...
The most likely pathways, or "scenanos," through which radioactive materials could be released to the accessible environment are described, together with the performance assessment (PA) approach used to evaluate those scenarios against the EPA standards and some of the results to date.
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The individual protection requirements limit the committed effective dose to any individual resulting from releases from the undisturbed repository to 0.15 milliSievert (15 mrem) per year.
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From page 17... ...
A disadvantage is that the Part 191 containment requirements do not differentiate between transport of radionuclides off-site in a pristine aquifer that is a likely exposure pathway and in the case of WTPP-transport via the Culebra Dolomite, in which the high content of dissolved solids makes the water unfit for human consumption. Quantitative Assessment of Human Intrusion Dealing quantitatively with human intrusion is a difficult issue.
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From page 18... ...
encompasses the overall process of assessing whether or not a waste disposal system meets a set of performance catena. For the WIPP PA, the system is a deep geologic repository disposal system in bedded salt for DOE TRU waste, and the performance criteria are various
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From page 19... ...
that permits comparison with the EPA release limits for radioactive waste disposal. The CCDF, a generally accepted form for depicting risk by a specific performance measure, was popularized by the Reactor Safety Study (U.S.
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) 10-5 10-4 10-3 10-2 10-1 10° 1o1 1o2 103 104 EPA Summed Normalized Releases, R FIGURE 2.l Hypothetical CCDF illustrating compliance with the containment requirements.
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Earlier performance results have been published in the 1992 PA (Sandia National Laboratories, 1992) and in the SPM analyses (Sandia National Laboratories, 1995~.
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study of the 1992 PA does provide some insight into the relative magnitude of release scenarios. CCDF curves summarizing radionuclide releases to the accessible environment resulting from cuttings removal and ground-water transport fall substantially below release limits promulgated by EPA.
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ground-water protection requirements. The indiviclual protection requirement considers the radiation dose to humans in the accessible environment for 10,000 years of undisturbed performance.
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leakage of brines containing radioactive materials up the shaft and/or through a disturbed rock zone around the shaft up to the Culebra Dolomite and flow to the 'defined accessible environment via the Culebra; and 2.flow of WIPP brines directly along anhydnte marker beds in the Salado Formation-salt. These scenarios are mentioned briefly here and represent mechanisms for potential release of radionuclides that underlie Me considerations in Chapters 3 and 4.
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From page 25... ...
Thus, for 12-inch diameter boreholes drilled at a rate of 50 boreholes per square kilometer per 10,000 years, direct cutting releases apparently are less than 4 percent of the allowable 25 limits. Even when allowing for increased release due to waste erosion by drilling mud and spallation, extraction of the waste as cuttings is unlikely to approach the release limits.
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24 ~ ~ age' ^~, ~ ~' ~ n Exploratory Doing Rig Rc = ._ . ~ = I E= I ~ ._ _ _ _ ~ ~ : O DRZ (note scale)
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From page 27... ...
and ~ 0-20 m2. The draft compliance document does note that "although the DRZ is modeled conservatively in this assessment, it is the subject of a modeling study, and assumptions and treatment of this region may be different in the final Compliance Certification Application" (DOE, 1 995a, p.
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From page 28... ...
This overly conservative assumption prevents the creep and healing behavior of the Salado halite from being properly included in past sensitivity analyses of WIPP performance. With effects such as DRZ reconsolidation excluded from a sensitivity analysis, an opportunity is lost to evaluate the full potential for cost-effective measures to demonstrate compliance.
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From page 29... ...
Although many analyses of radionuclide releases from WTPP have been made by Sandia National Laboratory and other DOE contractors, the radiation doses that could result have not been assessed for some reasonably identifiable scenarios and pathways. Most analyses of WIPP performance have focused on regulatory compliance with the EPA containment requirements, that is, calculations to estimate the quantity of radioactive materials that could be released across an arbitrary compliance boundary within 10,000 years.
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From page 30... ...
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From page 31... ...
pathway exists through the shallower Dewey Lake Red Beds. The committee believes that the potential for individual doses received by drinking water drawn from this formation, located closer to the surface than the Culebra, should be analyzed and documented.
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These topics are treated in the remaining chapters ofthe report. GENERAL QUALITY OF WIPP PERFORMANCE ASSESSMENT ACTIVITIES Development of the WIPP PA has been a pioneering effort: it was the first detailed assessment of an actual radioactive waste repository to be published and has been the mode} for many subsequent analyses worldwide.
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From page 33... ...
The value of information gained by such analysis must exceed the cost and risk of obtaining the information, but these trade-offs can be considered only if the sensitivity of repository performance to different waste characteristics is understood. Where costly waste characterization requirements appear to offer little value in terms of 33 ensuring health protection, DOE should seek to have the requirements reinterpreted.
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From page 34... ...
A quantitative answer to the degree of characterization required would emerge rigorously from PA calculations, using the release limits specified by EPA standards, which apply irrespective of whether the releases pose a risk to humans. Monitoring DOE is required to perform a monitoring study as part of the information to be submitter!
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From page 35... ...
CONCLUSIONS Perfo,~ance assessment has a major role to play in demonstrating compliance with EPA standards and providing assurance to the public that transuranic waste can be stored without posing a significant health risk to the public in the Waste Isolation Pilot Plant. Although performance assessment did not originate with WIPP, the project has done much to advance the development and applicability of PA to radioactive waste disposal.
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From page 36... ...
PA can provide guidance to waste characterization requirements. The impacts, both in terms of economics and of human exposure to the radioactive materials, can be significant.
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