| OAK RIDGE NATIONAL LABORATORY | ENERGY DIVISION |
| REPORT NUMBER |
ORNL-6783/R1
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| AUTHORS |
D. W. Lee et al.
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| SPONSOR |
Research sponsored by the U.S. Department of Energy
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Performance Assessment for Continuing and Future Operations at Solid Waste Storage Area 6 |
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This report is a revision to the radiological performance assessment (PA)
for the existing low-level waste (LLW) disposal facility, Solid Waste
Storage Area 6 (SWSA 6), at Oak Ridge National Laboratory.
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| BACKGROUND |
SWSA 6 has been used for the disposal of LLW generated at ORNL since
1974. Continued and future disposal operations at the Interim Waste
Management Facility (IWMF) in SWSA 6 are required to meet the
performance objectives of Order 5820.2A,
which include the
consideration of all wastes disposed of after September 26, 1988.
Wastes disposed of at SWSA 6 include a large number of radionuclides
in a variety of different disposal unit types. Procedures for
characterization, treatment, and packaging of wastes have changed
over the period of operations. While the initial PA, prepared in 1994,
was considered to be technically acceptable by DOE Headquarters, this
revision was required to address the changes in waste disposal
operations taken in response to the initial PA.
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| OBJECTIVE |
To demonstrate that SWSA 6 is in compliance with the performance
objectives of DOE Order 5820.2A and to provide the operating basis for
continuing and future disposal operations at IWMF.
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| APPROACH |
This revised PA was prepared to clearly demonstrate that SWSA 6
disposal operations meet the performance objectives of DOE Order 5820.2A.
The PA was revised to distinguish those disposal units which have
been closed from the ongoing disposal operations at IWMF. The
revised PA included all changes that had been made to disposal
operations after the completion of the initial PA and introduced
several additional changes to be made at IWMF to provide reasonable
assurance the performance objectives of the DOE order could be met
throughout the remaining operating life of IWMF. This revision of
the PA was prepared using new guidance from DOE Headquarters
that was much more prescriptive than the guidance available for the
initial PA.
The analysis for the closed disposal units at SWSA 6 was performed using the same basic model structure used in the initial PA but with several significant improvements. The closed disposal units were analyzed to determine the doses to an off-site individual, located outside a buffer zone roughly equivalent to the SWSA 6 facility boundary and surrounding the closed disposal units. Potential doses to an off-site individual were calculated and compared to a performance objective of 25 mrem/year from all exposure pathways, 10 mrem/year from atmospheric exposure pathways, and 4 mrem/year from drinking water pathways. Potential doses to an inadvertent intruder were also calculated for a variety of exposure scenarios and compared to a performance objective of 100 mrem/year for chronic exposures and 500 mrem for an acute exposure. The doses were calculated for all of the radionuclides reported to be in the inventory of the closed disposal units using the records in the ORNL Waste Management database. The portion of the dose limits not attributed to the closed disposal units was then used to calculate the waste loadings for the IWMF which would be allowable and still allow SWSA 6 to meet the performance objectives of DOE Order 5820.2A. The analysis was performed using a set of linked models. Each
model was consistent with the conceptual model of the performance
of the disposal facility to the extent that data were available
describing disposal facility performance. The natural processes
considered included the generation of leachate from the disposed
waste, the transport of contamination through the shallow subsurface,
and the transport of contamination in groundwater.
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| RESULTS |
The results of this revised PA demonstrated that all of the closed
disposal units meet the performance objectives of DOE Order 5820.2A.
Furthermore, the doses associated with the closed disposal units
were sufficiently low to allow for disposals of LLW at IWMF for
all 63 radionuclides considered in the PA. Allowable inventories
of waste for IWMF disposal were determined to be predominantly
limited by the consideration of inadvertent intrusion. The
existing disposals on IWMF were well below the allowable inventory
limits calculated in the analysis. Based on the analysis of the
uncertainty in the results, additional restrictions on the disposal
of problematic radionuclides were identified to provide additional
assurance the performance objectives of the order will be met
from all remaining waste disposal operations at IWMF.
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| CONCLUSIONS |
The results presented in the PA provide a reasonable basis for
concluding that LLW disposals at SWSA 6 provide adequate protection
to public health and the environment as expressed in the performance
objectives of DOE Order 5820.2A. The PA provides limits for continuing
and future operations at IWMF that will ensure that compliance with
the performance objectives of the order will be maintained in
the future.
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