tank closure topics · associated processing facilities. tank closure topics barriers slowing the...

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

Special accommodations:If you need this publication in an alternative format, please call 509-372-7950. Persons with hearing loss, call 711 for Washington Relay Service. Persons with speech disability, call 877-833-6341. Nuclear Waste Program

hanford@ecy.wa.gov * 800-321-2008

Toolbox, continued from p. 3

andbreakupthewaste.Ifthesluicersdonotremovewastetolessthan360cubicfeetofwasteremain-ing,thentheConsentDecreerequiresasecondtechnologybeusedtoremovemorewaste.

MARSiscurrentlyworkinginC-107andisexpectedtoremovewastetolessthan360cubicfeetwithallthetoolsincorporatedintoit.Thedirectwaterpressureandalargebackstopcanbothbeusedtomovemorewastetowardthepumpthananyotherretrievaltoolsusedtodate.

Retrievalplansvaryfromtanktotank;however,wasteretrievalisexpectedtobecompletedinC-Farmtanksby2014.Thecurrentplanistousethetoolsinthegraphicabove.ThewasteintheSSTswillbere-movedinthemostefficientmannerandwiththebestretrievaltools.Thetoolboxofretrievaltechnologiesisfairlyfull.Wehavehighexpectationsthatwasteretrievalwillbecompletedby2014.Doyou?

VisitourFacebookpagetoshareyourthoughtsonHanfordcleanupandtankclosure:www.facebook.com/HanfordEducation

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.