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Title: Unreviewed Disposal Question Evaluation: Waste Disposal in Engineered Trenches 3 and 4

Abstract

Revision 0 of this UDQE addressed the proposal to place Engineered Trench #3 (ET#3) in the footprint designated for Slit Trench #12 (ST#12) and operate using ST#12 disposal limits. Similarly, Revision 1 evaluates whether ET#4 can be located in and operated to Slit Trench #13 (ST#13) disposal limits. Both evaluations conclude that the proposed operations result in an acceptably small risk of exceeding a SOF of 1.0 and approve these actions from a performance assessment (PA) perspective. Because ET#3 will be placed in the location previously designated for ST#12, Solid Waste Management (SWM) requested that the Savannah River National Laboratory (SRNL) determine if the ST#12 limits could be employed as surrogate disposal limits for ET#3 operations. SRNL documented in this Unreviewed Disposal Question Evaluation (UDQE) that the use of ST#12 limits as surrogates for the new ET#3 disposal unit will provide reasonable assurance that Department of Energy (DOE) 435.1 performance objectives and measures (USDOE, 1999) will be protected. Therefore, new ET#3 inventory limits as determined by a Special Analysis (SA) are not required.

Authors:
 [1];  [1];  [1]
  1. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
Publication Date:
Research Org.:
Savannah River Site (SRS), Aiken, SC (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1414387
Report Number(s):
SRNL-STI-2013-00393
DOE Contract Number:
AC09-08SR22470
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES

Citation Formats

Butcher, T., Hamm, L., and Flach, G.. Unreviewed Disposal Question Evaluation: Waste Disposal in Engineered Trenches 3 and 4. United States: N. p., 2017. Web. doi:10.2172/1414387.
Butcher, T., Hamm, L., & Flach, G.. Unreviewed Disposal Question Evaluation: Waste Disposal in Engineered Trenches 3 and 4. United States. doi:10.2172/1414387.
Butcher, T., Hamm, L., and Flach, G.. 2017. "Unreviewed Disposal Question Evaluation: Waste Disposal in Engineered Trenches 3 and 4". United States. doi:10.2172/1414387. https://www.osti.gov/servlets/purl/1414387.
@article{osti_1414387,
title = {Unreviewed Disposal Question Evaluation: Waste Disposal in Engineered Trenches 3 and 4},
author = {Butcher, T. and Hamm, L. and Flach, G.},
abstractNote = {Revision 0 of this UDQE addressed the proposal to place Engineered Trench #3 (ET#3) in the footprint designated for Slit Trench #12 (ST#12) and operate using ST#12 disposal limits. Similarly, Revision 1 evaluates whether ET#4 can be located in and operated to Slit Trench #13 (ST#13) disposal limits. Both evaluations conclude that the proposed operations result in an acceptably small risk of exceeding a SOF of 1.0 and approve these actions from a performance assessment (PA) perspective. Because ET#3 will be placed in the location previously designated for ST#12, Solid Waste Management (SWM) requested that the Savannah River National Laboratory (SRNL) determine if the ST#12 limits could be employed as surrogate disposal limits for ET#3 operations. SRNL documented in this Unreviewed Disposal Question Evaluation (UDQE) that the use of ST#12 limits as surrogates for the new ET#3 disposal unit will provide reasonable assurance that Department of Energy (DOE) 435.1 performance objectives and measures (USDOE, 1999) will be protected. Therefore, new ET#3 inventory limits as determined by a Special Analysis (SA) are not required.},
doi = {10.2172/1414387},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month =
}

Technical Report:

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  • Because Engineered Trench #3 (ET#3) will be placed in the location previously designated for Slit Trench #12 (ST#12), Solid Waste Management (SWM) requested that the Savannah River National Laboratory (SRNL) determine if the ST#12 limits could be employed as surrogate disposal limits for ET#3 operations. SRNL documented in this Unreviewed Disposal Question Evaluation (UDQE) that the use of ST#12 limits as surrogates for the new ET#3 disposal unit will provide reasonable assurance that Department of Energy (DOE) 435.1 performance objectives and measures (USDOE, 1999) will be protected. Therefore new ET#3 inventory limits as determined by a Special Analysis (SA) aremore » not required.« less
  • The Closure Plan for the E-Area low-level waste facility assumes that dynamic compaction performed at the end of the 100-year institutional control period will adequately stabilize all waste in Slit Trenches. However, some non-crushable waste containers with significant void space will not be stabilized by dynamic compaction. These non-crushable containers will gradually corrode, eventually collapse and cause the final closure cap to subside resulting in an increase of the infiltration rates. After subsidence occurs, the waste zone will be significantly reduced to concentrate waste in the lower portion of the slit trench, therefore increasing waste concentration. The trench subsidence maymore » have an adverse impact on the 1000-year compliance specified in DOE Order 435.1. This study addresses the issue of trench subsidence, evaluates the resulting concentrations at the hypothetical 100-m well against those obtained based on the PA approach, and provides the maximum number of trenches that can subside without causing the well concentrations to be out of compliance.« less
  • Operational inventory limits for the disposal of solid low-level waste in Slit Trenches 1-7 were established by the Special Analysis (SA) performed by Collard and Hamm (2008). To determine disposal limits for the Slit Trenches, the SA followed the methodology used in the 2008 PA (WSRC, 2008) which assumed that the inventories in each trench were instantaneously placed in 12/1995, which is the date when SLIT1 began operation. The 2008 SA analyzed the impact from placing storm-water runoff covers simultaneously over Slit Trenches 1-7 at 5, 10 and 15 years after the inventory was introduced. To include a measure ofmore » conservatism in the limits, the lowest of the limits calculated for any storm-water runoff cover placement time or that calculated in the original 2008 PA was chosen as the operational limit for each radionuclide. Through the availability of funding provided by the American Recovery and Reinvestment Act (ARRA), storm-water runoff covers were placed over Slit Trenches 1-5 in December 2010. SRNL was requested to perform a UDQE for this accelerated action. Table 1 below lists the operational dates for Slit Trenches 1-5 and the time elapsed between when the first waste package was disposed in each Slit Trench and when the storm-water runoff covers were placed. As shown in Table 1, SLIT1 was covered 15.0 years after the date of the first waste package disposal. SLIT2 was covered 9.2 years after the date of the first waste package disposal in SLIT2 which falls within the window of {+-} 1.0 year within which the 2008 SA cover time analysis was assumed to be valid (Crowley and Butcher, 2008). Therefore, the analysis of SLIT1 and SLIT2 in the 2008 SA is considered adequate. However, the cover timings for SLIT3, SLIT4 and SLIT5 are from 2.2 to 1.6 years beyond the nearest cover time of 5 years assumed in the 2008 SA analysis and fall outside of the acceptable one-year margin. Therefore, an additional study was conducted by Collard et al. (2011) that assessed the impact on Slit Trench performance from a covering date that is between 12/2010 and 9/2011. Accelerated placement of storm-water runoff covers over Slit Trenches 1-5 put the cover timing outside of the range considered in the 2008 SA (Collard and Hamm, 2008) which establishes Slit Trench disposal limits. Results from a recent study (Collard et al., 2011) demonstrate that the actual cover installation in December 2010 produces acceptable Slit Trench performance. Additionally, covering Slit Trench 5 separately from Slit Trenches 6 and 7, which will be operationally closed at a later date, does not adversely affect performance of the operationally closed trenches.« less
  • Solid low-level waste disposal operations are controlled in part by an E-Area Low-Level Waste Facility (ELLWF) Performance Assessment (PA) that was completed by the Savannah River National Laboratory (SRNL) in 2008 (WSRC 2008). Since this baseline analysis, new information pertinent to disposal operations has been identified as a natural outcome of ongoing PA maintenance activities and continuous improvement in model simulation techniques (Flach 2013). An Unreviewed Disposal Question (UDQ) Screening (Attachment 1) has been initiated regarding the continued ability of the ELLWF to meet Department of Energy (DOE) Order 435.1 performance objectives in light of new PA items and datamore » identified since completion of the original UDQ Evaluation (UDQE). The present UDQE assesses the ability of Solid Waste (SW) to meet performance objectives by estimating the influence of new information items on a recent sum-of-fractions (SOF) snapshot for each currently active E-Area low-level waste disposal unit. A final SOF, as impacted by this new information, is projected based on the assumptions that the current disposal limits, Waste Information Tracking System (WITS) administrative controls, and waste stream composition remain unchanged through disposal unit operational closure (Year 2025). Revision 1 of this UDQE addresses the following new PA items and data identified since completion of the original UDQE report in 2013: New K d values for iodine, radium and uranium; Elimination of cellulose degradation product (CDP) factors; Updated radionuclide data; Changes in transport behavior of mobile radionuclides; Potential delay in interim closure beyond 2025; and Component-in-grout (CIG) plume interaction correction. Consideration of new information relative to the 2008 PA baseline generally indicates greater confidence that PA performance objectives will be met than indicated by current SOF metrics. For SLIT9, the previous prohibition of non-crushable containers in revision 0 of this UDQE has rendered the projected final SOF for SLIT9 less than the WITS Admin Limit. With respect to future disposal unit operations in the East Slit Trench Group, consideration of new information for Slit Trench#14 (SLIT14) reduced the current SOF for the limiting All-Pathways 200-1000 year period (AP2) by an order of magnitude and by one quarter for the Beta-Gamma 12-100 year period (BG2) pathway. On the balance, updates to K{sub d} values and dose factors and elimination of CDP factors (generally favorable) more than compensated for the detrimental impact of a more rigorous treatment of plume dispersion. These observations suggest that future operations in the East Slit Trench Group can be conducted with higher confidence using current inventory limits, and that limits could be increased if desired for future low-level waste disposal units. The same general conclusion applies to future ST’s in the West Slit Trench Group based on the Impacted Final SOFs for existing ST’s in that area.« less
  • The Saltstone Facility 0.2 Curie/gallon MAVRC (Mixer At Vault Roof Concept) Project will utilize various pieces of process equipment that have not been analyzed from a Performance Assessment perspective for future disposal. The proposed activity will involve the disposal of Saltstone process equipment in an empty Vault 1 cell and encasing the equipment in clean (nonradioactive) grout. An examination of this activity indicates that the disposal of up to 20 pieces of each specified component should not affect the assumptions, results, and conclusions of the approved Performance Assessment (PA) and Special Analyses (SA) for Saltstone, and that the activity ismore » within the bounds of the Disposal Authorization Statement (DAS).« less