The Tumulus Disposal Demonstration (Tumulus 1), Tumulus 2, and the Interim Waste Management Facility (IWMF) are being utilized to demonstrate the acceptability of tumulus disposal technology while at the same time providing disposal capacity for solid low-level radioactive waste (LLW) generated at Oak Ridge National Laboratory (ORNL). The planning process resulting in selection and ultimate implementation of tumulus disposal technology for the Oak Ridge Reservation is still on-going and consists of four major phases: alternatives identification and evaluation; technology demonstration; limited operational implementation; and full operational implementation at a new site. This document discusses these phases. 2 figs., 1 tab

Jordan, E.A.

Mezga, L.J. (Oak Ridge Gaseous Diffusion Plant, TN (United States))

Radcliffe, L.L. (USDOE, Washington, DC (United States))

Van Hoesen, S.D. (Oak Ridge National Lab., TN (United States))

Jordan, E. A.

Radcliffe, L. L.

Van Hoesen, S. D.

Mezga, L. J.

UNT Digital Library

__/' CONF-9110229--IDE92 000434OVERVIEW OF TUMULUS DESIGN,CONSTRUCTION, AND OPERATING EXPERIENCEE. A. Jordan, DOE/HQL L. Radcliffe, DOE/ORS. D. Van Hoesen, Martin Marietta Energy Systems, Inc.L J. Mezga, Martin Marietta Energy Systems, Inc.MARTIN MARIETTA ENERGY SYSTEMS, INC.Oak Ridge, TennesseePrepared for the U. S. Department of EnergyUnder U. S. Government Contract DE-AC-O5-840R21400DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither the United States Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsi-bility for the accuracy, completeness, or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privately owned rights. Refer-ence herein to any specific commercial product, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof. The viewsand opinions of authors expressed herein do not necessarily state or reflect those of theUnited States Government or any agency thereof.MASTER.... ,.,.,r,.,.u rtr:rUl._qflrlIMENTIS UNLIMITE9UI_I IIlDU I lUWl u, ........INTRODUCTIONThe Tumulus Disposal Demonstration (Tumulus I), Tumulus II, and the Interim Waste ManagementFacility (I'_,'3fF) are being utilized to demonstrate the acceptability of tumulus disposal technolo_while at the same time providing disposal capacity for solid low-level radioactive waste (LLW)generated at Oak Ridge National Laboratory (ORNL). The planning process resulting in selectionand ultimate implementation of tumulus disposal technology for the Oak Ridge Reservation is stillon-going and consists of four major phases: (1) alternatives identification and evaluation, (2)technolo_ demonstration, (3) limited operational implementation, and (4) full operationalimplementation at a new site.The alternatives evaluation conducted as part of the Low-Level Waste Disposal Development andDemonstration Program (LLWDDD) considered a full range of technical alternatives (shallow landburial to above- and below-grade engineered disposal facilities) based upon the fundamental technicalability of each alternative to meet individual facility performance objectives. As a result of thisevaluation, above-grade engineered disposal was identified as the preferred technology formanagement of approxSmately 30,000 ft:' per year of predominantly short half-life, mixed fissionproduct LLW. However, a number of technical and operational questions remained to be answered,thus establishing the need for the tumulus demonstration project.Tumulus I was designed as a technology demonstration project. Tumulus I construction began in1986 and was operated from 1987-89. Tumulus II, designed as a bridge between the technologydemonstration (Tumulus I) and limited operational implementation (IWMF), was constructed during1989 and operated during 1990-91. As such, design and operational modifications incorporated"lessons learned" from the demonstration phase. Construction of IWMF began in May 1990 andoperation is expected to begin in late 1991 and last through 1996. IWMF is considered "limitedoperational implementation" became it is being constructed on an existing disposal site <i.e., SolidWaste Storage Area 6 (SWSA 6) at ORNL> and because waste certification actMties as beingdefined for the new LLWDDD facilities will not be fully implemented. Full operationalimplementation _511begin with operation of the new LLW Disposal Facility beginning in 1997pending completion of the project Environmental Impact Statement which identifies tumulustechnology as the preferred alternative for short half-life LLW.PROJECT PLANNINGThe strategic planning process that culminates in the identification, selection, construction, andttltimate operation of treatment, storage, and disposal facilities for ali types of LLW generated on theOak Ridge Reservation was conducted under the LLWDDD Program. This program consideredmanagement of various concentrations of short half-life radionuclides generated principally at ORNLand long half-life radionuclides (principally uranium) generated at the Y-12 Plant and the Oak RidgeK-25 Plant. The overall schedule of major activities under the LLWDDD Program is shown inFigures 1 and 2.As indicated previously, the planning process resulting in selection and implementation of tumulusdisposal technology for the disposal of short half-life LLW is still on-going and consists of four1phases: (1) alternative identification and evaluation, (2) technolo_ demonstration, (,3) limitedoperational implementation, and (4) full operational implementation. These phases are discussed inthe following sections.Alternative Identification and EvaluationThe alternatives evaluation phase consisted of the identification of the range of technical alternativesto be considered, identification of evaluation criteria for ranking the alternatives, and the actualevaluation and ranking of the alternatives. The technical alternatives considered were narrowed downto seven using broad screening criteria. These criteria considered the technical feasibility of actualimplementation (e.g., do the hydrology and geology of the site allow implementation) and theappropriateness of the technology to the types of LLW to be managed. The seven alternativesconsidered were (1) landfill, (2) shallow land burial, (3) earth covered tumuli, (4) above-gradeconcrete structures, (5) deep trenches, (6) augured shafts, and (7) below-grade concrete structures.Criteria used for evaluating the alternatives considered the ability of each technology to meet thefundamental facility performance objectives, the anticipated performance of the technology, theacceptability of the technology to the regulators and the public, and the anticipated cost. Facilityperformance objectives were based on the requirements of Department of Energy Order 5820.2A"Radioactive Waste Management" which defines dose limits to the public and the intruder from LLWdisposal facilities. In addition, State of Tennessee groundwater protection standards were alsoconsidered. In evaluating the anticipated performance of the technologies, the operating record ofeach technology at other facilities was re,,iewed and, to the extent practical, extrapolated to the OakRidge Reservation. Maintenance and monitoring requirements, complexity of operation,and actualperformance history were reviewed. Regulatory and public acceptability were gauged based ondiscussions with sta.te and federal regulators, reviews of technology selection processes underway inthe state compacts and in foreign countries, and comments received during the public scoping meetingfor the project Environmental Impact Statement. Finally, general construction, operation, andmaintenance cost information were considered where available. Based upon this evaluation, above-grade disposal in an engineered facility (i.e., tumulus disposal technology) was identified as thepreferred alternative for short half-life radionuclides and i._being carried forward as such in theproject Environmental Impact Statement.The Environmental Impact Statement, which is currently being prepared, is a key component of thetechnology selection process. It documents the alternatives considered, the anticipated impacts, andthe basis for the decision on the _._zhnology selected. The Environmental Impact Statement iscurrently planned to be issued in draft form in September 1991 with the final report targeted forApril 1993.Technology' DemonstrationPreliminary evaluations indicated that tumulus disposal technology offers significant potential toovercome Oak Ridge Reservation (ORR) site limitations related to a shallow, complex groundwaterflow system and a surface water system that provides for rapid movement of any releases off-site(Figure 3). The concrete vaults provide enhanced confinement and structural stability for the waste.The concrete pad provides a "cut-offf for communication with groundwater, thus making the approachsuitable for areas with shallow depths to groundwater. The proposed disposal configuration alsoprovides capability to monitor ali water flo_,s that may come in contact with the waste and facilitatcsrecovery should disposal unit performance not be acceptable.As a result, the _ _VSA 6 Tumulus Disposal Demonstration was conducted to develop experience andinformation to help in evaluating the suitability of this technology for the management of solid LLWon the ORR (Figures 4 and 5). Information was developed on environmental and health,operational, and construction aspects of the technolo_.The Tumulus demonstration unit was constructed with monitoring features which should ultimatelyallow measurement of the environmental performance of this technology. The curbed pad on whichthe waste is placed was designed to collect ali water which may come in contact with the w.a_tecontainers. This water drains from the pad to a monitoring station where the flow is measured andsamples collected. In addition, a plastic liner was placed under the pad to allow monitoring of anyinadvertent leakage and to provide an additional barrier against groundwater contamination.Monitoring features were also included in the cap design to allow evaluation of its performance.One major goal of the demonstration was to gain experience in the construction of the Tumulus Unit.The Tumulus Technology is a significant departure from the past and current practices employed atthe ORR for Low Level Waste Disposal (i.e., earth moving and trenching operations). Further, theTumulus Demonstration required unusually large amounts of reinforcing steel to provide a very highstrength and durable concrete pad. Also, extraordinary construction techniques as well as QAprocedures were required to meet the performance criteria for the Tumulus Unit.In order to meet demonstration objectives, the following criteria were developed for the facility:- must have at least 2-ft. depth to highest recorded groundwater elevation;- may not be located on top of old disposal areas;- may not be located in areas suitable for below-grade disposal;- land area should be large enough to accommodate earthen cover 6-ft thick ,_th 4:1slope to sides;- should be located in level area (e.g., slope < 10%);- may not be constructed on fill area;- must be accessible by fork lift and crane from staging area;- should be located as far as possible from surface drainage features;- location should be compatible with overall SWSA 6 surface water monitoring scheme;- lifetime should be approximately 300 years;- should be constructed to support 10-16 fr,of waste contained in concrete vaults, soiloverburden of 4-6 ft, concrete cover of up to 2 ft., and earth moving equipment;- should be constructed with curbed perimeter and drainage systg-mto accommodatecollection of rainwater during loading operations and collection of leachate afterclosures; and . --- should be sized to hold approximately one year waste generation.Actual experience from the Tumulus I and II and IWMF is provided in later sections of the paper.Limited Operational ImplementationAs a result of the successful implementation of the technology demonstration phase, limitedoperational implementation of the technology is being undertaken in the form of the IWMF.Implementation is considered "limited" for several reasons: (1) the IWMF is located in SWSA 6 (thecurrent LLW disposal site at ORNL) and did not require a new site selection process, (2) the spaceavailable in SWSA 6 limits the size and the operational life of the IWMF to approxfmately 5 to 6years, (3) waste acceptance criteria and characterization programs that will be developed for the newfacilities are not yet in piace. Within that context, construction is currently being finalized andoperation is scheduled to begin in late 1991 or early 1992.Full Operational ImplementationFull operational implementation will occur in the form of the new LLW Disposal Facility currentlyplanned for SWSA 7 at ORNL, contingent upon completion of the Environmental Impact Statement.As currently planned, facility construction will begin in 1994, and it ,,,,'iiiprovide approximately 20years of disposal capacity, beginning in 1997.TUMULUS OPERATING EXPERIENCE AND LESSONS LEARNEDTumulus disposal technology_ has been successfully utilized at ORNL for almost four years, and todate approximately 50,000 ft" of solid LLW have been disposed of via the Tumulus. The followingsections summarize the important "lessons learned" from tumulus operations to date.Pad ConfigurationThe size of disposal pads have been reduced from 65-ft by 110-ft on Tumulus I to 60-ft by 90-ft inTumulus II and IWMF. The pads were reduced in size to eliminate the construction difficultiesassociated with the integral pour approach which was utilized. The 30-mil plastic liner utilized onTumulus I was eliminated on later units due to construction difficulties and significant in-leakage ofgroundwater from the underpad gravel system. The pad thickness was increased to 15-in. forTumulus II and IWMF tc, accommodate a three high waste vatilt stack.Drain Line GalleryDifficulties were encountered in both Tumulus I and II with leakage of the below-grade drain piping.A concrete utility tunnel system has been adapted for use as a drain line gallery for the IWMF toprovide access to the drain lines for inspection and monitoring. The gallery entrance will be extendedto the earthen cover surface to provide access after closure.Disposal VaultsThe handling mechanisms for the disposal vaults were changed form forklift slots on the Tumulus Ivaults to choker cable lift rings for the Tumulus II. Significant difficulties were encountered with theforklift movements during loading of Tumulus I which resulted in damage to the vault edges andincreased vault loading times. No difficulties have been encountered with the removable lift ringsv,'hich are currently being utilized. Chamfers were added to ali edges of the Tumulus II vault whichhas reduced the chipping and spalling noted with the Tumulus I vaults.The efficiency of loading of the containerized LLW into the vaults and backfilling with grout hasbeen improved by the development of special hold-down f'ex'turesto prevent container float.Operational MonitoringMonitoring has been conducted for worker exposures during vault loading and placement operations.To date worker exposures have been kept within control limits and appear to actually be reducedfrom exposures experienced during the previously utilized trench loading operations. It appears thatthe concrete vaults provide significant shielding for the workers once the waste is placed inside.Monitoring of the pad drain discharges has noted only one significant radioactivity release. Elevatedtritium levels were detected in the drain from Tumulus II in June 1991. A suspect leaking vault wasidentified and removed in July 1991. Gross beta levels from Tumulus I are slightly above backgroundlevels, due to the presence of Potassium-40 (K-40). The K-40 is thought to be the result of leachingof naturally occurring materials form the large concrete surface areas present in the tumulus disposalsystem.The elevated K-40 levels appear to be consistent with the high pH levels noted in the pad drainwater. The pH levels are in the range of 8-10, and appear to be dependent on the number of vaultsplaced on the pad. The drain lines from both pads have been closed and water is being collected andhauled to treatment since the high pH violates the regulatory discharge limits. The impact ofplacement of the planned earthen cover on the pH levels is currently being evaluated.COST SUMMARYThe estimated cost for the alternatives identification and evaluation phase is appro:dmately $7 million.This is a working estimate since the Environmental Impact Statement has yet to be finalized.A summary of the cost of the design, construction, and operation and the tumulus demonstrationprojects is provided in Table 1. Design costs include Title I'and II efforts, as well as additionaldocumentation on construction experience that was developed by the demonstration program as apart of Title III design. Construction costs include the f'Lxedprice contract for site preparation,tumulus pad and monitoring station construction, as well as in-house costs for monitoring instrumentprocurement and installation, and utility hookups. The vault costs reflect the f'Lxedprice manufacturecontract for the vaults currently being utilized. Operating costs include waste container placementin the vaults, concrete backfill, vault lid placement and sealing, and vault placement operations. Thecost of the cover is based on estimates developed during a conceptual cover design effort conductedduring 1987.It is estimated that the design, construction,_ operation, and closure costs for the tumulusdemonstration phase are approximately $62/fr' on an "as disposed" basis. Projected design,construction, operation,, and closure costs for the IWMF on an "as disposed" basis are approximately$88/ft 3 . Costs on an 'as generated" basis could be much lower, depending on the degree of wastecompaction achieved in waste container loading. It should be recognized that these costs may changesignificantly for future tumuli as a result of site characteristics, technology evolution, and effects ofscale.TABLE 1TUMULUS DISPOSAL DEMONSTRATION COST SUM.",LARYTumulus I IWMF- Design $ 60.000 $ 200,000- Tumulus Construction $ 180.000 $ 2,650,000- Vault Manufacture $ 234.000 $ 4,300,000- Tumulus Operations $ 660.000 $ 4,800,000- Tumulus Closure $ 425.000 $ 2.300,000Total $1,559,000 $14,250,000$62/ft3 $88/ft3I|° , ..... •..... ..... 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Overview of tumulus design, construction, and operating experience

Overview of tumulus design, construction, and operating experience

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