| OAK RIDGE NATIONAL LABORATORY | ENERGY DIVISION |
| REPORT NUMBER |
ORNL-6929
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| AUTHORS |
D. W. Lee, J. D. Tauxe, A. S. Icenhour, D. C. Kocher, R. J. Luxmoore
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| SPONSOR |
Research sponsored by the U.S. Department of Energy
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Composite Analysis for Solid Waste Storage Area 6 |
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This report is an analysis of all sources of radioactive contamination
that could interact with the sources of contamination present in wastes
in Solid Waste Storage Area 6 (SWSA 6) at Oak Ridge National Laboratory.
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| BACKGROUND |
In its Recommendation 94-2 the Defense Nuclear Facilities Safety Board
suggested that the U.S. Department of Energy (DOE) should evaluate all
contributing sources of
contamination as part of regulating the disposal of low-level
radioactive waste (LLW). In response to this recommendation, DOE has
required the preparation of a composite analysis (CA) for every LLW
disposal facility. The CA must consider all wastes in the ground that could
interact with the releases of contamination from an existing or planned
disposal facility. The CA and the performance assessment (PA) for a disposal
facility form the technical basis for issuing a Disposal Authorization
Statement by DOE Headquarters that permits the disposal of LLW waste.
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| OBJECTIVE |
To provide an estimate of the potential cumulative impacts to a
hypothetical future member of the public from SWSA 6 disposal operations
and from all other sources of radioactive material in the ground on the Oak
Ridge Reservation (ORR) that may interact with contamination originating
in SWSA 6.
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| APPROACH |
The projected annual doses to a hypothetical future member
of the public from all contributing sources is compared to a primary dose
limit of 100 mrem/year and a dose constraint of 30 mrem/year. For
projected doses greater than the primary dose limit, an options analysis
is required to identify alternatives for reducing the dose to levels
below the limit. For projected doses less than the primary dose limit
but greater than the dose constraint, an options analysis and an ALARA (as
low as reasonably achievable) assessment for further dose reduction is
required. For projected doses less than the dose constraint, an ALARA
assessment may be warranted, but only if it would be cost-effective.
Dose assessments were conducted for the first 1000 years after disposal for comparison with the primary dose limit and the dose constraint, consistent with the CA guidance issued by DOE Headquarters. The potential doses were evaluated at a point of assessment consistent with the DOE land use boundary, which is the edge of the ORR 20 km (12 miles) downstream from the confluence of White Oak Creek (WOC) with the Clinch River. Potential changes in the DOE land use boundary were considered as part of the sensitivity and uncertainty analysis included in the CA. The sources of contamination considered in the CA included all of the sources identified in the Melton Valley Remedial Investigation and those sources of contamination in Bethel Valley identified by the Remedial Action Program. The data used in the analysis were identified using the data quality objectives process, and resulted in the definition of radioactive source inventories of important radionuclides in the WOC watershed in Melton and Bethel Valleys. Estimated inventories were used in the absence of available data by extrapolating from known sources in SWSA 6. Potential peak release rates to groundwater and surface water were estimated using a simple first-order leaching model. Transport of radioactive materials in water was the only release pathway considered in the CA because historical data on releases of radioactive material for the ORR and the findings of the PA have shown that releases by other pathways are insignificant compared to releases in water. The potential doses were determined by estimating the potential travel
times for the peak mass release of each radionuclide in the inventory from
the source of contamination to surface water, and accounting for the decay
of each radionuclide in transit. The mass release to surface water was
diluted in the discharge of WOC and in the Clinch River. The potential
doses from each radionuclide were determined by assuming this to be
contaminated drinking water source for an individual.
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| RESULTS |
The results determined in the CA indicate that the potential dose from
all contributing sources in the watershed (0.5 mrem/year) is significantly
less than the dose constraint assuming the current ORR land use boundary.
For the case where the land use boundary is changed to allow access to the
shoreline of the Clinch River, the potential dose (500 mrem/year) exceeds
the primary dose limit at White Oak Dam.
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| CONCLUSIONS |
SWSA 6 meets the requirements for the CA for all existing sources of
contamination that could contribute to the potential dose from LLW
disposals, providing the current system of land use controls is maintained
on the ORR. Changes in the land use plan for the ORR that would include
the release of land along the shoreline of the Clinch River would require
the implementation of alternatives to reduce potential exposures to
individuals in the future. Current actions being considered by the CERCLA
program are directed toward addressing this need.
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Available to DOE and DOE contractors from the Office of Scientific and Technical Information, P.O. Box 62, Oak Ridge, TN 37831; for prices call 423-576-8401. Available to the public from the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161; for prices, call 703-487-4650.