mapping nuclear verification - princeton universityaglaser/pu131-mapping-verification-2017.pdf ·...

MappingNuclearVerification

TamaraPattonandAlexanderGlaserABSTRACT.Progress innucleararmscontroltowardlowernumbersofweaponswillrely inparton the availability of viable treaty verification options that account for the entire life cycle of aweapon.Thenatureof theseverificationoptionsdependson thedirection that future reductionstake(e.g.whetherreductionsemphasizewarheadcountingorfissilematerialbalances)aswellasthetypesofcompromisesthattreatynegotiatorsareabletoachieveintermsofbalancingtranspar-encyandsecurity.Asresearchersandpolicymakersworktomaketheseverificationoptionsavaila-ble,thereisasignificantneedforaconceptualmaptofacilitateorientationandprioritization,andtohelpexplainthecontextinwhichparticulartechnologiesarerelevant.Thispaperpresentsafic-tional statemodel–called “Nu”–asa tool to illustratevariousverificationstrategies in termsofbothoptionsandneeds.Nuhasbeenbuilttohostanuclearfuelcycleandweaponlifecyclethatisrepresentativeofmoststatesthatpossessnuclearweapons,includingtheelementsofproduction,assembly,deployment,disassembly,anddisposition.AlsoillustratedinNuarepossiblepre-existingverificationregimes,e.g.IAEAsafeguards,NewSTARTmeasures,andCTBTmeasures.Asatoolforachievingabirds-eyeview,aprimaryusefortheNumodelistoidentifyandhelpaddresspotentialdiversionpathwaysforfissilematerialorweaponsthroughverificationtechnologiesandapproach-es,withvaryinglevelsofintrusivenessandscope.Exampleapproachespresentedinthepaperad-dress futurearmscontrol treatyobjectives, includinganext incrementalbilateral treatybetweenRussia and the United States, aswell as a state joining the Treaty on the Prohibition of NuclearWeapons.Eachoftheapproachesoffersstrengthsandweaknessesintermsofoveralleffectiveness,andeachexhibitsuniquebenefitsanddrawbacksfromtheperspectivesofthehostsandinspectors.Readers should consider these approaches a startingpoint fordiscussion, as each canbebrokendownandrecombinedinnumerousotherconfigurations.1.BackgroundWithover15,000nuclearweaponsstillinexistenceinninecountries,nucleararmscontrolanddis-armamenteffortswillrely inpartontheavailabilityofviableverificationoptionsthatcanbetai-loredtomeettheneedsoffuturetreatyinstruments.WiththeUnitedStatesandRussiapossessingthevastmajorityoftheseweapons,theseneedsmayarisemostimmediatelyfornucleararmscon-trolmeasuresfollowingtheNewStrategicArmsReductionTreaty(NewSTART),whichremainsinforceuntil2021withthepossibilityofafive-yearextension.GivenNewSTART’sexclusivefocusonstrategicdelivery systems (specifiedby range), follow-onmeasureswill requirenewsolutions todealwithnon-deployednuclearweapons,weapons awaitingdismantlement, non-strategicweap-onsandweapon-gradefissilematerialstockpiles.

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AnotherpathwayforreducingweaponstowardtheireliminationliesinthenewlyadoptedTreatyon the Prohibition of NuclearWeapons. This treaty,while establishing a number of prohibitionsrelatedtonuclearweaponpossession,allowsforastatethathasdecidedtodisarmtojoinasaStateParty and negotiate a protocol to ensure the verified and irreversible elimination of its nuclearweaponprogram. It furtherspecifies that statesparties to the treatyshalldesignateacompetentinternationalauthoritytoconductthisverification.Giventhecomprehensivenatureofsuchapro-cess,challengesrequiringnewsolutionswillarise,particularlysurroundingmeanstoensurethateliminationisastransparentandirreversibleaspossible.Otherpathways forreductionsanddisarmamentarealsopossible, including throughmultilateralagreementsthatmayemergebetweennuclearweapon-possessingstates,orthroughunilateralde-cisionsbyindividualstatestodisarm.Researchersarethereforetaskedwithdevelopingavarietyofoptions tomeet thediversityofpossiblescenarios.This task includesoptimizing individual tech-nologiestomaximizetheirsimplicityandrobustnessandtominimizetheirintrusiveness,aswellasbuildingcohesiveconfigurationsof technologiesandapproaches thatcancover thediversesetoffacilitiesandobjectivesunderanyagreement.2.MapandWebsiteOverviewAsresearchersandpolicymakersworktomakeverificationoptionsavailableforthescenariosde-scribedabove,thereisasignificantneedforaconceptualmaptofacilitateorientationandprioriti-zation,andtohelpexplainthecontextinwhichparticulartechnologiesarerelevant.Ourresearchgrouphasthereforecreatedafictionalstatemodel–called“Nu”–asatooltodevelopandillustratevariousverificationstrategies(availableat:www.verification.nu). Nuhasbeenbuilttohostanu-clear fuel cycle and weapon life cycle that is representative of most states that possess nuclearweapons.Asatoolforachievingabirds-eyeview,theNumodelcanbeusedtodevelopcomprehen-siveverificationsolutionsbyidentifyingandaddressingpotentialdiversionpathwaysforweaponsor fissilematerial throughverification technologies andapproaches,with varying levels of intru-sivenessandscope.TheNumappingprojectisalsointegratedwithaparallelprojectonvirtualreality.WhileNuallowsforthedevelopmentandassessmentofverificationapproachesfromabroad,strategicperspective,virtualenvironmentsallowresearcherstodivealeveldeepertofurtherinvestigatetechnical,archi-tecturalandproceduraldetailsassociatedwitheachuniquefacilitytype.Researcherscanexamineverificationapproacheswithinanimmersivevirtualenvironment,allowingwalk-throughsandper-son-to-person interaction, including theoperationofequipmentand the full simulationofvirtualradiation fields and real-time detector response. Combining Nu and virtual reality can allow forsubstantial and flexible collaborationamongst researchgroupsandgovernmentsworking to findsolutionstoverificationchallenges.Theprojectwebsitehostsagrowinglibraryofverificationtechnologiesunderdevelopmentintheresearchcommunity.Verification technology innovationcentersonansweringchallenges suchasdetermining theaccuracyofbaselinedeclarations, authenticatingaweaponwithout learningany

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classifiedinformationaboutit,andensuringtheabsenceofundeclaredtreaty-accountableitemsorfacilities.Theresearchcommunityhasmadestridestowardanswerstothesechallenges,butmoreworkandengagementareneededmovingforward.Thewebsitewillthereforeexistasoneavailablespace to aid in organizing and coordinating complementary verification technology developmentefforts.The facilityset featured in theNustatemodelcontains thekey facilitiesandelementsassociatedwithanuclearweaponprogram,includingtheelementsofproduction,assembly,deployment,dis-assembly,anddisposition.Themaplayoutremainsflexible,allowingforthefutureincorporationofadditionalfacilitiesrelevanttonuclearweapondevelopment,suchasresearchfacilitiesandthoseassociatedwithimportantnon-nuclearcomponentsofnuclearweapons.Initscurrentstateonthewebsite,theNumapprovidesanoverviewofkeyfacilitiesandhighlightssomeoftheverificationissuesassociatedwitheach.Thesehighlightsaresummarizedinthefollowingsections,whichpro-videanoverviewofNu’ssixregions.Figure1.The“Nu”VerificationLandscape

Forinformationonindividualfacilities,viewtheinteractiveversionofthemapatwww.verification.nu.Region1:Production |Theproductionregion features theessential infrastructure foranuclearfuelcycle.Afteruraniummining,conversionfacilitiesdealwithprocessinguraniumoreconcentratetoproduceuraniumhexafluoride(UF6),agaswhichwillbeabletoundergoenrichmentandwhichmustbeundersafeguards.Inrecentyears,the‘startingpoint’ofInternationalAtomicEnergyAgen-cy(IAEA)safeguardshasbeenmovedfurtherbacktoincludepurifieduranylnitrate,anintermedi-ateformofuraniumusedintheconversionprocess.Next,anenrichmentfacilityprocessesuranium

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toincreasetheamountofuranium-235inthematerial,withmostmodernenrichmentplantsusinggascentrifugetoseparateuraniumisotopes.Aftermaterial is fabricatedintofuelandburnedinareactor, spent reactor fuel is chemically treated to extract plutoniumanduranium,which canbereusedasnuclearfuelorusedinweapons.Safeguardsatthesefacilitiescanbechallenging,asnu-clearmaterialcannotbeaccountedforonanitem-by-itembasis(insteadexistinginbulkform),andinspectorscannotdirectlyaccessmaterialbecauseoftheitsradioactivity.Region 2:Assembly | At a nuclear warhead assembly facility, weapon-grade fissile material ismanufactured into weapon components and combined with non-nuclear components. Access toassemblyfacilitieswillbemostrestrictiveduetotheexposureofclassifieddesigndetails.Thein-trusivenessofverificationmeasuresmaydependheavilyonwhetherastateisstillactivelyproduc-ing or modernizing weapons. If production has ceased, verification might include more basicmeasures toverify shutdown. Ifproduction isactive,verificationwouldbemorecomplex,withaboundarysystemservingasonepossibility.Region3:Deployment |Deployment sites refer tomilitarybaseshostingnuclearwarheads andtheirmeansofdelivery, includingbombers, submarines,and land-basedmissiles.Theregionalsoincludesanumberofsmallerstoragesites,referringtositeswherewarheadsarestoredinclosedcontainers,conceivablyatorneardeploymentsitesandundermilitarycustody.Whileverificationmeasureshavebeenestablishedfordeliverysystems,therearenotyetmeasuresforverifyingwar-heads,which,inadditiontobeingpresentondeliverysystems,mayalsobepresentinnearbystor-age and maintenance facilities. Verification measures that attempt to account for warheads, inaggregatenumbersandpossiblywithunique ID systems,mayneed tobeable to account for themovementandmaintenanceoftheseitemsthroughoutandbetweenstorageanddeploymentsites.Perimeterorportalmonitoringtechniquescouldeitherfocusonindividualstoragesitesoronmuchlargerdeploymentsites.Region4:Dismantlement |Warheaddismantlementfacilitiesprimarilydealwiththeseparationofaweapon’sfissilematerialcomponentsfromnon-nuclearcomponents,includinghigh-explosives,whichcanentail rigoroussafetyandaccessrequirements.Disassemblycan takeplace inmultiplestages and over extended time periods, possibly requiring continuity-of-knowledge or chain-of-custodyverificationmeasures.Verificationmeasuresatdismantlementfacilitiesmaybecomplicat-edbythefactthatseveralstateshavedual-purposeassemblyanddisassemblyfacilities.Region5:Disposition |Adispositionorconversion facility isconcernedwith furtherprocessingfissile-materialextractedfromnuclearweapons.Dispositionmayinvolverenderingfissilematerialintoanunusableform,throughmeasuressuchaspermanentstorageorvitrification.Thismayalsoinclude downblendingHEU to LEU andmore drasticmeasures such as irreversibly changing theshapeofweapon components (for example, “pit squashing”). Verification challengesmay includehowtoconcealper-itemmassandisotopicswhilemaintainingadequateaccountancyorcontinuity-of-knowledge.

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Region6:Hinterland|TheHinterlandrepresentsanyareainastatewiththepotentialtohostun-declared fissilematerial, nuclearweapon componentsornuclearweapons.VerificationmeasuresshouldinpartbedesignedtopreventthediversionofitemstotheHinterlandortheillicitproduc-tionof items in theHinterland.Verification topreventdiversion can include chain-of-knowledge,accountancy, boundary or provenancemeasures. Detectionmeasures could include challenge in-spectionsorremotesensing.Ingeneral,verificationmeasuresshouldalsoincludemeanstodetectundeclaredsitesandactivitiesthatmayexistindependentlyfromthedeclaredinfrastructures;thiscouldinclude,inparticular,satelliteimageryorwide-areaenvironmentalmonitoringorsampling.3.ExampleApproachesThissectiondetailstwoexamplesofhowNucanbeusedtoassembleaverificationapproachforagivensetof treatyobjectives.The firstexample focusesonahypothetical follow-onarmscontroltreatytoNewSTARTconcernedwithwarheadlimits.Thesecondexamplepresentsahypotheticalcaseofanuclear-weapon-possessingstatejoiningtheTreatyontheProhibitionofNuclearWeap-onsandeliminatingitsnuclearweaponprogram.Thedistinctobjectivesofeachtypeofagreementinfluencethenatureofverificationmeasures.Ver-ifyingreductionsorlimitsonwarheadswillbemoreeasilyreversiblegiventhattheinfrastructureneededtorebuildthearsenalwouldlikelyremainintacttosupportthemaintenanceoftheremain-ing force. Verification of reductions or limits also faces the challenge of longevity anddurability,giventhatanyverificationmeasuresinthedeployment,disassemblyanddispositionregionswouldneedtobemaintainedoveralongperiodtoretainconfidenceincompliance.Any“breaks”betweensuccessivearms-controlagreementswouldintroduceuncertaintiesaboutcompliance;anexampleofthisistheIntermediateRangeNuclearForces(INF)Treaty,whereintheabsenceofthenowex-tinctverificationsystem,uncertaintiesaboutcompliancehaveemerged.Finally,verificationofre-ductionsorlimitsposesthechallengeofgreatersecrecythatislikelytobedesiredbypartiestoanagreement. Given that some nuclear weapons are understood to remain deployed, parties willtherefore likelywant to avoid giving an adversary toomuch information about deployment pat-terns,andverificationmeasureswouldneedtotakethisintoaccount.Alternatively,verifyingtheeliminationofanuclearweaponprogrammaybemorestraightforward.Inparticular,thechoicetoeliminateanuclearweaponimpliesalesserneedforsecrecysurround-ingdeploymentpatterns.Inthiscontext,warheadsmightbeabletobeuniquelyidentifiedtopro-videgreaterconfidence that theyhavebeeneliminated.Elimination isalsodistinct in that itmayinitiallyinvolveinspectionsatawiderarrayoffacilities,includingthoseassociatedwithproductionandmaintenance.However,ifthereductionsarepartofasustainedmovetowardelimination,mostof thesemeasureswouldbe temporary,with anyenduringverificationmeasuresbuildingon theInternationalAtomicEnergyAgencysafeguardssystem,includingmeasuresincludedinacompre-hensivesafeguardsagreementandadditionalprotocol.

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Each strategybelowoffersparticular strengths andweaknesses in termsof overall effectiveness,andeachexhibitsuniquebenefitsanddrawbacksfromtheperspectivesofthehostsandinspectors.Readersshouldconsiderthesestrategiesstartingpointsfordiscussionandfurtherdevelopment,aseachcanbeexpanded,brokendownorrecombined innumerousotherconfigurationsdependingontheprioritiesandavailableresourcesineachcase.Example1:WarheadLimitAgreement|Afollow-onagreementtoNewSTARTcouldincludeanincremental reduction to U.S. and Russian nuclear forces consisting of limits on warheads. TheObamaadministrationproposedin2013thatanextbilateralagreementcouldincludeareductionofaboutone-thirdofeachcountry’sarsenal,includingreductionstonon-strategicnuclearweapons.NewSTART’sverificationregimefocusesonlyontheverifiedconversionoreliminationofstrategicdelivery systems (i.e.missiles and bombers), and does not dealwith verification at thewarheadlevel.Afollow-ontreatywouldthereforefacenewverificationchallenges,includinghowtoverifytheeliminationofindividualwarheads,non-deployeddeliveryvehicles,andnon-strategicweapons.The verification tasks inherent in an agreement of this naturewould include, among others, as-sessingbaselinedeclarationsofnon-deployedwarheadsandaccountingandmonitoringthefissilematerial components extracted from them. While there are numerous ways to approach thesetasks,thebasicchallengeliesinbalancingtheneedstoachieveinspectorconfidencewhileminimiz-ing intrusiveness.Thebasesetofmechanisms for thisexampleverificationapproach includesanextensionoftheNewSTARTnon-repeatingidentifiersystemtowarheads,1hasheddeclarationsforassessingbaselinedeclarationsandaportalmonitoringsystemformonitoringextractedfissilema-terialcomponents(Figures2and3). Figure2.Mainmechanismsusedinwarheadlimitagreementverificationstrategyexample

Fromlefttoright:Non-robustwarheadIDsystem,hasheddeclarationsforbaselinewarheaddeclarations,andportalmonitorforperimetercontrolsystem.Images:FrommariuseviaTurbosquid(left)andfromPrincetonNuclearFuturesLab(centerandright).Tosupport thecountingofwarhead totals, thisexampleverificationstrategyconsidersanexten-sionoftheidentifier(ID)systemfordeliveryvehiclesunderNewSTARTtowarheads.NewSTARTdefinesanIDasanon-repeatingalphanumericnumberthathasbeenappliedbytheinspectedpar-tytothefirststageofaballisticmissileortoaheavybomberandtotheoutsideofanyassociatedcanisterusedtomaintain,storeortransportthemissile.Additionally,thesameIDisreplicateddi-

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rectlyonornearlaunchersinaplaceaccessibletoinspectors.Theagreementdoesnotcallforanytamper-preventionmeasuresandallows the state todetermine theexact sizeof the ID.2Underawarheadlimitagreement,thissystemmightbeextendedtowarheads.ThiscouldinvolveapplyinganIDtobothawarheadanditsassociatedcontainer.AsintheNewSTARTprocess,thehostcoun-trywouldthentrackandreportthisIDasrequiredasthewarheadmovesthroughoutthecountry.ThisprocesscouldbelimitedtotrackingtheIDandwarheadatthelevelofbases,storagesitesorfacilities.Underaninspectionprotocolandwithincertainconstraints(someofwhicharedetailedinthefollowingsections)inspectorscouldbeallowedtoreadtheIDsatsitesassociatedwithnon-deployed warheads during inspections. Given the unlikelihood that inspectors would be able toreadanIDonawarheadif itisdeployedandonadeliveryvehicle, inspectorscouldsimplybeal-lowedtoviewalistoftheIDsofwarheadsthataredeployedatabaseunderinspection.Figure3.ExampleverificationstrategyforawarheadlimitagreementusingtheNuMap

Thisexamplestrategyutilizesanon-robustwarheadIDsystemforaccountinginthedeploymentanddisassem-blyregions,hasheddeclarationsforbaselinewarheaddeclarationsinthedeploymentregion,andaperimetercontrolsystemforsecuringthedisassemblyprocess.Proceduresandtechniquestoconfirmupperlimitsonthenumberofnuclearwarheadswithoutre-vealingsensitiveinformationaboutdeploymentpatternsmaybeseenasanimportantverificationtask as warheads are further reduced. One mechanism for facilitating this objective is throughhashed declarations, which are privacy-preserving declarations thatmight be usefully combinedwith the IDsystemforwarheads.Hasheddeclarationswouldnot list the locations(orotherrele-vant data) of treaty-accountable items in cleartext. Instead, only, a hash (or “messagedigest”) ofeachentrywouldbemadepublic.Suchahashismuchshorterthantheoriginalmessageitself,but

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theunderlyingcryptographichashfunction isdesignedsuchthat it isextremelydifficult to findavalidmessageforagivenhashortoconstructtwodifferentmessagesthatproducethesamehash.3In preparation for an onsite inspection, the inspecting partywould announce the storage or de-ploymentlocationthatitwouldliketoinspect,andthehostpartywouldthenprovidethecleartextforalltreaty-accountableitemsthatarepresentattheselectedsite.ThiscleartextcouldincludetheIDsforwarheadspresentatthegivensite.Especiallyifconductedonshort-noticeandoverseveraliterations,theseinspectionscanbuildconfidencethatthehoststateisreportinganaccuratenum-berofweapons.Confidence in any agreed reductions could be supported by a perimeter control and portal-monitoring process, which would monitor vehicles and containers entering the complex. Suchscreeningcouldbebasedononeorseveralsensors,forexampleradiographicimagingtoobtaintheshapeofobjects,orradiationmeasurementdevicestodetectthepresenceofnuclearmaterialssuchasuraniumorplutonium.4NewSTARTprovidesneutron-countcriteriafordeterminingthatanob-ject isnotanuclearweapon,theinverseofwhichcouldprovideaninitialmeasureforidentifyingwarheadsenteringaportal.5Asweaponsenterthisperimeter-controlledcomplex,theirIDswouldbe recorded. After this point, disassembly of theweapons could take placewithout an inspectorpresentas longas the fissilematerialcomponentsremain in theperimeter-controlledarea.Upondisassembly,theIDsshouldbetransferredtothecontaineroftheassociatedfissilematerialcom-ponents. Either periodically or at a later point in the agreement’s timeline, the inspection teamcouldperformaninspectiontoreviewandaccountfortheextractedweaponcomponentsandfis-silematerial.Theseitemscouldconceivablybeescortedbyinspectorsortrackedwithothertech-nologiestoaseparateconversionordispositionsite,whereinspectorscoulddirectlymeasurethematerialonceitreachesanunclassifiedform.WhilethestrategydescribedprovidesassurancebeyondwhatisofferedinNewSTARTforverify-ingwarhead limits and reductions, there are still numerous gaps that should be recognized andwhichcanbeillustratedusingNu(Figure4).Theseincludedivertingfissilematerialextractedfromweaponseitherbackintonewweaponproductionortoanundeclaredsite.Additionally,giventhatIDs are not linked towarheads in physically uniqueways, there remains the risk thatwarheadscouldbedivertedfromtheproductionordeploymentregionsandreplacedbyotheritemsbearingthesame IDas longasrobustunique identifiers (UID)can’tbedemonstratedand fielded for thispurpose.Thesystemisalsoweakenedbytheuncertaintythatwarheadsbeingcountedanddisas-sembledarereal.Additionaltechnologies(includingthosededicatedtowarheadconfirmation),ap-proachesorinspectiontypescouldbedesignedandaddedtodealwiththeseremainchallengesasneeded.

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Figure4.Remainingdiversionpathwaysforwarheadlimitagreementverificationstrategy

Theexampleverificationstrategyhasanumberofremainingdiversionpathwaysandwaystoreconstituteweapons.Additionaltechnologiesorapproacheswouldneedtobeincorporatedtoclosethesegaps.Example2:WeaponEliminationAgreement|Thisnextexamplepresentsaverificationapproachforthehypotheticalcaseofastateeliminatingitsnuclearweaponprogram,forexample,aspartofjoiningtheTreatyontheProhibitionofNuclearWeapons.Thestrategyexhibitsanumberofvaria-tions fromthepreviousexample, includingbyestablishingcontinuity-of-knowledgeon individualitemsratherthanusingaperimetermonitoringsystem.Giventhattheobjectiveofthisagreementwould be complete and irreversible elimination of a nuclear arsenal, there is less of a need formeasurestoprotectsensitiveinformationrelatedtodeploymentpatternsandweaponmovements.This approach thereforeaims tooffer greater certainty thatwarheads,havingbeen tracked fromtheirdeliverysystemstothepointofconvertingordisposingoftheextractedfissilematerial,areindeedirreversiblydismantled.Thebasesetoftechnologiesforthisexampleverificationapproachinclude buddy tags for assessing baseline declarations, a passive inspection system with infor-mationbarrierexperimentalforconfirmingtheauthenticityofwarheads,andamodaltestingsys-temformaintainingcontinuity-of-knowledgeonanitem(Figure5).For the taskof assessingbaselinedeclarations, this strategyemploysbuddy tags,whichcouldbeusedatbothdeployedandnon-deployedweaponsites.Giventhatattachinguniqueidentifiersdi-rectly towarheadscouldbeproblematicdue toarangeofconcernsby thehostrelated tosafety,security, and intrusiveness, buddy tags function as tokens that are physically separate from thetreaty-accountableitem.6Thehostmustbeabletoproduceonetagforeachitemwithoutdelay,andverificationwouldthereforerelyonshortnoticeinspections.Sensorsinthetagwouldshowthatit

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hadnotbeenmovedtotheinspectedsiteaftertheinspectionwasdeclared(forexample,withinthelast24–48hours).Thesetagscanbeusedatbothdeployedwarheadsitesandnon-deployedwar-headsitesgiventherequirementthattheyonlyneedtobewithinthesamecomplexastheassociat-edweapon,andcouldinfactbeinacompletelyseparatebuilding.Figure5.Maintechnologiesintheweaponeliminationagreementexampleverificationstrategy

Fromlefttoright:Buddytagsforbaselinewarheaddeclarations,informationbarrierforwarheadconfirmation,modaltestingforchain-of-knowledge.ImagesfromPrincetonNuclearFuturesLab.Buddy tag inspectionswould ideallybe supportedbyawarheadconfirmation technology tohelpensure that the tags are associatedwith realweapons.For the taskof confirmingwarheads, thisstrategy employs a passivewarhead confirmation systembased on gamma spectrometry and aninformationbarrierusingatemplate-matchingapproach.7Template-matchingfirstentailsrecord-ingaradiationsignaturefromawarheadtrustedtobegenuine.Thesignatureofaninspecteditemisthencomparedagainstthereferencesignature,anddependingontheagreementofthetwosig-natures,thepassorfailsignalappears.Atawarheadstoragesite,theinspectionteamcanrandomlyselectacontainertoperformaconfirmationmeasurementusingtheinspectionsystem. Theexamplestrategyalsoenvisionsthattheinspectionsystemwiththeinformationbarrierwouldbeusedforwarheadsjustpriortodisassembly.Afterconfirmation,inspectorswouldthenneedtoremainnearby a secureddismantlement areauntil disassembly is complete in order tomaintaincontinuity-of-knowledgeontheextractedfissilematerialcomponent(e.g.“pit”).Afterdisassembly,continuity-of-knowledge on the extracted fissilematerial components could be achieved throughuniquelyidentifyingpit-containercombinationsthroughtheuseofmodaltesting.Modaltestingisaspecializedformofresonantvibrationanalysisoftenusedforthepurposeofstructural identifica-tion, conditionmonitoring, and damage detection. It has been postulated that amodal vibrationsignaturemightbeusedtoidentifyaparticulartreaty-accountablecontaineroritem-containersys-tem,orprovideevidenceoftampering.8Amodaltestingsignaturewouldthereforebeacquiredbytheinspectionteamimmediatelyfollowingthewarheaddisassemblyprocess.Thecontainercouldthenbeplacedininterimstorageandwouldnotneedtobeexaminedbyinspectorsagain(throughasecondmodaltestingmeasurement)untiljustpriortoconversionordisposition.

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Figure6.ExampleverificationstrategyforaneliminationagreementusingtheNuMap

Thisexamplestrategyutilizesbuddytagsinthedeploymentregionforbaselinewarheaddeclarations,confirma-tionmeasurementsinthedeploymentregionandjustpriortodisassemblywithaninformationbarrier(IBX),andamodaltestingmeasurementimmediatelyfollowingdisassemblytomaintaincontinuity-of-knowledgeontheextractedfissilecomponentsuntilthepointofconversionordisposition.Overall,thisstrategyprovidesahigherlevelofconfidencethatitemsoriginatingfromdeliverysys-temsareconvertedordisposedofdue inparticulartotheuseofawarheadconfirmationmecha-nisminboththedeploymentregionanddismantlementregion.However,itisaresource-intensivestrategy thatwouldrequireasignificant levelof inspectorpresence throughout theprocess.Thismightbemitigatedbyaddingadditionaltechnologiesormonitoringapproachestothestrategytoreducetheloadoninspections.Inparticular,inspectorloadmightbesignificantlyreducedifsolu-tionsaredevelopedtoensurecontinuity-of-knowledgefromaconfirmedwarheadtoitscontainer-ized fissile material components. Given that warhead disassembly can be a lengthy process,technicalorproceduralsolutionsatthisparticularjuncturewouldbebeneficial.

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4.OutlookAsresearchersworktodeveloptechnicalandpolicysolutionstofuturearmscontrolanddisarma-mentchallenges, itremains importantto increaseunderstandingoftherelationshipsbetweenex-istingandpossiblefuturetreaties,andtoexplorethepotentialsynergismsofdifferentverificationtechnologiesandapproaches.TheexamplesshownhereillustratehowNucanbeusedtoassembleandevaluateaverificationapproachthatconsidersthewider landscapeofacountry’s infrastruc-ture,andhowitcanilluminateremaininggapsandchallengestowardtheimprovementofthegivenstrategy.FutureresearchusingNuwouldseektobuildadditionalstrategyoptionsusingdifferentcombinationsofverificationtechnologiesandapproaches,includingboththosedescribedhereandadditionaltoolsfeaturedonthegrowinglibraryoftechnologiesontheNuwebsite.Inclosecoordi-nationwithourteam’sworkonvirtualreality,futureeffortswillalsobegearedtowardrefininganevaluation framework to aid inunderstanding the relative strengths anddeficiencies ofdifferentverificationstrategiesatbothbroadanddetailed facility levels,withthegoalofgeneratingviableoptionsetsforfuturearmscontrolanddisarmamentagreements. 1UnderSTARTandNewSTART,identifiersarecalled“uniqueidentifiers”(UID),buttheseidentifiersarehostsuppliedandhostapplied.AsJimFullernoted,theSTART“end-gameunderBushIAdministrationresultedininspectingpartyhigh-technologytaggingbeingsacrificed,”JimFuller,USSTARTTIDDevelopmentProgram:TheQuestforExtremeSecurityUniqueIdentifiers(1986–1992),April2006,www.inmm.org.2SeeprovisionsonuniqueidentifiersinNewStrategicArmsTreaty,ProtocolandAnnexonInspectionActivi-ties.Availableatwww.state.gov/t/avc/newstart/c44126.htm.3MonitoringNuclearWeaponsandNuclear-ExplosiveMaterials:AnAssessmentofMethodsandCapabilities,NationalAcademyofSciences,Washington,DC,2005;AlexanderGlaserandSébastienPhilippe,“HashedDec-larationsofNuclearWarheadInventoriesforEarlyCommitmentandNon-intrusiveVerification,”58thAnnualINMMMeeting,IndianWells,California,July2017.4J.P.Harahan,On-SiteInspectionsUndertheINFTreaty:AHistoryoftheOn-SiteInspectionAgencyandINFTreatyImplementation,1988–1991,On-SiteInspectionAgency,Washington,DC,1993;D.Mureretal.,“FLASHPortals:RadiationPortalMonitorSNMDetectionusingTimeCorrelationTechniques,”54thAnnualINMMMeeting,July2013.5DefininganuclearweaponisacomplextaskandisexploredfurtherinAlexanderGlaser,“CeciN’estPasuneBombe:TowardaVerifiableDefinitionofaNuclearWeapon,”58thINMMAnnualMeeting,IndianWells,Cali-fornia,July2017.6SabinaE.Jordan,BuddyTag’sMotionSensingandAnalysisSubsystem,SandiaNationalLaboratory,Albu-querque,NewMexico,1991;S.DeLand,A.Glaser,J.K.Brotz,A.Kim,D.Steingart,andB.Reimold,MinimallyIntrusiveVerificationofDeepNuclearWarheadReductions:AFreshLookattheBuddy-TagConcept,57thAnnualINMMMeeting,Atlanta,Georgia,July2016.7J.Yan,A.Glaser,NuclearWarheadVerification:AReviewofAttributeandTemplateSystems,Science&GlobalSecurity,23(3),2015,scienceandglobalsecurity.org/archive/sgs23jieyan.pdf.8ThispreliminaryworkhasmainlybeenconductedbytheUKAtomicWeaponsEstablishment(AWE).SeeHelenWhite,PhilipDaborn,PaulaHayden&PhilipInd,“TheUseofModalTestingwithinNuclearWeaponDismantlementVerification,”Science&GlobalSecurity,22(2),2014.