| OAK RIDGE NATIONAL LABORATORY | ENERGY DIVISION |
| REPORT NUMBER |
ORNL/TM-13401
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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 the Class L-II Disposal Facility |
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This report is a radiological performance assessment (PA) for the proposed
Class L-II Disposal Facility (CIIDF) on the Oak Ridge Reservation (ORR).
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| BACKGROUND |
Approximately 10,000 m3/year of low-level radioactive waste (LLW) is
managed each year on ORR. The proposed CIIDF will handle a relatively small
volume of this quantity. These wastes are expected to include a large number of
radionuclides, most of which are expected to have radionuclides with half-lives
less than 30 years. Wastes disposed of at CIIDF will be characterized and
certified by waste generators using waste acceptance criteria that are to be
developed from the results of this PA.
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| OBJECTIVE |
To provide data that will provide the basis for evaluating the performance of
the CIIDF and provide reasonable assurance that the performance objectives of
DOE Order 5820.2A will be met in the disposal of LLW at CIIDF.
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| APPROACH |
This PA considered radionuclides likely to be present in wastes to be
disposed of at CIIDF, and considered in detail those radionuclides with
half-lives greater than 5 years. Each radionuclide considered in
detail was analyzed by use of a series of models representing site-specific
behavior at CIIDF, to determine the maximum allowable inventory that could
be present on a tumulus pad. Scenarios examined were routes of contaminant
transport and inadvertent intrusions. The models used for analysis were the
Unified Transport Model (UTM), the SOURCE1 model, the PADSIM model, and the
FTWORK model. The results from the computer modeling were used to determine
the maximum concentration of each radionuclide in waste corresponding to the
performance objective for water resource protection of 4 mrem/year. The
calculated maximum concentration was then converted to the maximum allowable
inventory for each pad at CIIDF.
Estimates of the maximum allowable inventory on each pad which satisfies the performance objectives for inadvertent intrusion were calculated for the most restrictive scenarios for the CIIDF. The maximum allowable inventory for each radionuclide was then set based on the most restrictive limit calculated from the inadvertent intruder and environmental transport calculations. The analysis for CIIDF required the use of assumptions -- about the physical and chemical properties of engineered and geologic materials, the closure of the disposal facility, and the application of annual averages of data representing processes and events of short duration -- to supplement the available site characterization data. These assumptions were selected to provide a reasonable yet conservative representation of facility performance and were based on the limited information available. The methodology used to analyze the performance of CIIDF was based on the
available data about the waste anticipated to be disposed of at CIIDF, the
disposal methods to be used at CIIDF, and the CIIDF site characteristics.
Since the results were calculated to ensure that the performance objectives
were satisfied for each radionuclide, operation of the facility with waste
acceptance criteria consistent with the maximum allowable inventories ensures
that the performance objectives are satisfied.
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| RESULTS |
The results determined in this PA indicate that of the 60 radionuclides analyzed,
35 were limited by the surface water or the groundwater pathway. The results were
calculated to the time of maximum dose with the understanding that a time of
10,000 years would be appropriate for establishing a time of compliance.
Only one radionuclide had a peak after the 10,000-year time of compliance
(10Be), and all but four radionuclides had reached the their peak by 1,000
years. The analysis of direct intrusion indicated that extended periods of
institutional control would increase the maximum allowable inventories of 9 of
the 25 radionuclides limited by intrusion.
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| CONCLUSIONS |
The results presented in this PA provide a reasonable basis for evaluating the
performance of CIIDF and provide reasonable assurance that the performance
objectives of DOE Order 5820.2A will be met for the disposal of LLW at CIIDF.
Continued work to reduce uncertainties and improve the methodology used to
analyze the performance of CIIDF are likely to relax the allowable limits on
inventory determined in the analysis.
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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.
Document prepared by the Energy Division, Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the U.S. Department of Energy under contract DE-AC05-96OR22464. Neither the U.S. government nor any person acting on behalf of the U.S. government assumes any liability resulting from the use of the information contained in this document or warrants that such use will be free from privately owned rights.