Nuclear Waste Program Publication 11-05-012 October 2011
In This IssueBarriers slowing the spread of contamination
What’s in the toolbox for retrieval?
Why It Matters
The 586-square-mile Hanford Site is located in south-central Washington along the Columbia River. Hanford’s mission included defense-related nuclear research, development, and weapons production activities from the early 1940s to approximately 1989. During that period, Hanford operated a plutonium production complex with nine nuclear reactors and associated processing facilities.
Tank Closure TopicsBarriers Slowing the Spread of Contamination
Eachyear,EcologyandtheU.S.Dept.ofEnergymeettodiscussinterimmeasuresforprotectingtheenvironmentuntilcleanupiscompleteatHanford.Theimplementationofinterimbarriersovertankfarmsisaresultofthosemeetings.
Untilthewasteisretrievedfromthesingle-shelltanks(SSTs)andthetanksareofficiallyclosed,soilcontaminantswillcontinuetomovetowardground-water,drivenbynaturalprecipitationandinfiltration.AsthecurrentscheduleforSSTretrievalextendsoverthenextfewdecades,interimbarrierswereconstructedovertwotankfarms,TandTYfarms.
Thebarrierscollectanddrainanyprecipitationawayfromthetankfarmsandintoadjoininguncontaminatedareas(Tinterimbarrier)orintoanevapotrans-pirationpond(TYinterimbarrier).
Theseinterimbarriersarebeingmonitoredtodeterminetheirperformanceintheshallowvadosezone.Thevadosezoneistheareabetweenthegroundsurfaceandthewatertable.
Whilethesebarriersdonotstopcontinuedtransportofcontaminantsinthedeepvadosezone,interimbarriersreducethevolumeofwateravailabletofurtherspreadcontaminants.
Continued p. 3 - see Toolbox
What’s in the Toolbox for Retrieval?
The2010ConsentDecreedeclaredthatwasteretrievalbecompletedfortheremaining10C-Farmsingle-shelltanks(SSTs)bySeptember2014.TheU.S.Dept.ofEnergy(USDOE)OfficeofRiverProtection(ORP)knowsitwilltakesomegoodplanning,efficientretrievaltools,andtimelyimplemen-tationtoreachthatdeadline.Sometoolsaresimple,othersintricateandcomplicated.
Insometanks,thetoplayerofwasteissimilartochunkyordriedmud.Inothertanks,thetoplayerisadissolvablesolid,likeananimalsaltlickblock.
Continued p. 2 - see Barriers
Providing the Washington State Department of Ecology’s views on Hanford tank closure activities
FormerlyUpdate: C-Farm Closure Volume2,Issue2
Nuclear Waste Program Publication 11-05-012 October 2011
Tank Closure Topics (formerlyUpdate: C-Farm Closure) Volume 2, Issue 2
Barriers continued from p. 1
ExtensivesoilsamplingandmonitoringwelldataintheHanfordtankfarmsshowscontaminationdistributedthroughoutthevadosezone.
Ecologydoesn’tthinkthevolumeofcon-taminantsbelievedtohaveleakedfromtheSSTs,orspilledthroughoutyearsoftankfarmoperations,isbigenoughtoinfiltratethroughtheentirevadosezonetogroundwater.That’sadepthmorethan200feetbelowthetanks!Butwebe-lievewateraddedtothesoilfromnaturalprecipitation,andbothplannedandun-plannedreleasesofwater,hascontributedsignificantlytodrivingreleasedcontami-nantstogroundwater.
ATri-PartyAgreementchangepackagetoMilestoneM-45-98-03wassignedinMarch2001.Threenewmilestoneswereadded:M-45-56,M-45-57andM-45-59.Theyaddressedinterimandcorrectivemeasuresthatwouldminimizetheadditionofliquidthatcoulddriveexistingsoilcontamina-tiontogroundwater.
Oneobjectivewastoreducethevolumeofunplannedreleasesofliquidstothesoil.Historically,unplannedreleasesofwatertosoilaroundtankfarmshaveincluded:
1.Floodingofthetankfarmsfromrapidrunoffandinfiltrationofsnowmelt(usuallyasaresultof Chinookwinds).2.Acuteandchronicleaksfromwaterdistributionlinesinandaroundtankfarms.3.Testingoffirehydrantsbyturningthemonandallowingdischargetosoil.4.Washingcontaminantsintothesoiltoreducehazardstoworkers.5.Hydro-excavation(diggingwithahigh-pressurewaterstream).6.Dustcontrol.
Atwo-stageapproachwasadoptedtocorrectthefirsttwo:1.Constructasystemofbermsandgutterssurroundingeachtankfarmtodivertrunofffromthetank farms.2.Testallwaterdistributionpipelinesinandaroundthetankfarms.Thoseinneedofrepairwere remediated;thosenolongerneededwerecutandcappedtopreventfurtherreleasesofwater. Most,ifnotall,ofthesepipelineswerewellpasttheirdesignlife.
Thelastfourdriverswerestoppedbyadoptingproceduresprohibitingtheactivities.
Theseinterimmeasureswerecompletedin2001and2002.InterimbarriersarebeingconsideredinthenearfutureattheSX,BXandBYtankfarms.
Theinterimbarriersarenotthefinalremediationofthesetankfarmsandwillnotaffectpermanentcorrec-tivemeasuresthatwillbeimplementedwhenthetankfarmsareclosed.
Nuclear Waste Program Publication 11-05-012 October 2011
WMA-C Closure Actions
Complete2019
Tri-Party AgreementDates for TankClosure
2003 - First SST emptied - C-106, followed by C-203
2014 - Complete WMA-CClosure Demo
2019 - Waste Treatment Plant begins treating waste
2040 - Complete retrieval of waste-from all SSTs
2043 - Complete closure of all SSTs
Current C-Farm timelines are based on landfill closure.
Barriers to water intrusion, will be placed over tank farms which will prevent the spread of contamination left in the soil.
Toolbox, continued from p.1
Bothtypesofwastecanbebrokenapartanddislodgedfromthetankwithwaterandpressure,likebeingdousedwithafirehose.The“firehose”processiscalledmodifiedsluicinganduseshigh-pressurewa-terjetsplacedthroughrisersintothetank.Thewaterbreaksupandmovesthewastetowardapump.Modifiedsluicingusesliquidwasterecycledfromdouble-shelltanks.Thisreuseofliquidreducestheoverallretrievedwastevolume.Also,anenhancedmodifiedsluicingmethodwasrecentlydeveloped.Withthisnewimprovement,thejetsareloweredveryclosetothewastesurfacetobreakupthewasteparticleswithmoreforce.
Ifthewastebecomesdifficulttobreakup,itmaytakealargertooltoaidinwasteremoval.TheFOLDTRACKtractorhasbeensuc-cessfullyusedintheSSTsandisreadyforfurtherdeployment.TheFOLDTRACKisaremotely-operated,track-mountedsystemthatusesawidebladetomovewastefromthebottomofthetanktoacentralpump.Thefrontofthisequipmentisfittedwithtwowaterjet-tingsystemstohelpmovewaste.Theequipmentcanactuallyfoldopenafterbeingloweredthrougha12”diameterrisermakingitcon-venienttopositionintheSSTs.Operatorsdirectthetractor’smove-mentremotely,fromatraileroutsideofthetankfarm.ControlledmovementoftheFOLDTRACKallowstheoperatorstodirectwasteoutofthereachofmodifiedsluicingjetstothecentralpump.
Insometankwasteremovaloperations,alargerbut“gentler”toolisnecessarytoreach,breakupandmovethewasteoutofthetank.ThistooliscalledtheMobileArmRetrievalSystem(MARS).TheMARScanbeusedintanksthataresuspectedtohaveleakedorhavequestionableintegrity.Thecompletesystemincludesaroboticarm,acentralpumpandancillaryequipmenttotransferthetankwaste.Thearmhasawiderangeofmotionandatelescopingca-pabilitytoreachallpartsofthetank.Itusessmallvolumesofhighpressureliquidstomoveandbreakupthewaste.OneMARSunitwillbedesignedwithavacuumattheendofthearmtoassistinwasteremoval.
ChemicaldissolutionwillbeanotherretrievaltooltoremovewastefromtheSSTs.Thisprocessconsistsofmanysteps,includingwash-ingthewastewithwater,addingchemicalslikesodiumhydroxide,soakingandpumping.Theexactsequenceandtimingoftheindi-vidualdissolutionprocessesiscommonlydeterminedfromlaboratorytestingwithanactualwastesample.
ModifiedsluicingwassuccessfullyusedintankC-103.Wastewasretrievedtolessthanoneinch(depth)ofwaste.Enhancedsluicerswiththeextendablearmwillbeplacedinatleastthreetanks.Itisexpectedthatthewasteinthesethreetanksishardandcementedandwillbenefitfromtheabilityofthesluicingarmstoreachclose
Toolbox, continued on p.4
Tank Closure Topics (formerlyUpdate: C-Farm Closure) Volume 2, Issue 2
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Toolbox, continued from p. 3
andbreakupthewaste.Ifthesluicersdonotremovewastetolessthan360cubicfeetofwasteremain-ing,thentheConsentDecreerequiresasecondtechnologybeusedtoremovemorewaste.
MARSiscurrentlyworkinginC-107andisexpectedtoremovewastetolessthan360cubicfeetwithallthetoolsincorporatedintoit.Thedirectwaterpressureandalargebackstopcanbothbeusedtomovemorewastetowardthepumpthananyotherretrievaltoolsusedtodate.
Retrievalplansvaryfromtanktotank;however,wasteretrievalisexpectedtobecompletedinC-Farmtanksby2014.Thecurrentplanistousethetoolsinthegraphicabove.ThewasteintheSSTswillbere-movedinthemostefficientmannerandwiththebestretrievaltools.Thetoolboxofretrievaltechnologiesisfairlyfull.Wehavehighexpectationsthatwasteretrievalwillbecompletedby2014.Doyou?
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C-Farm is the first waste management area scheduled for closure. Retrieving the waste to 360 cubic feet or less as required in the Tri-Party Agreement will be challeng-ing and take many different tools. The current schdeule is shown below.