ML16316A002
| ML16316A002 | |
| Person / Time | |
|---|---|
| Site: | Texas A&M University |
| Issue date: | 11/10/2016 |
| From: | Mcdeavitt S Texas A&M Univ |
| To: | Alexander Adams, Patrick Boyle Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 2016-0057 | |
| Download: ML16316A002 (30) | |
Text
Nuclear Science Center 1095 Nuclear Science Road, 3575 TAMU College Station, TX 77843-3575 Tel. (979) 845-7551 1
NUCLEAR SCIENCE CENTER Dr. Sean M. McDeavitt Director, TEES Nuclear Science Centerp Texas A&M University Texas A&M Engineering Experiment Station 1095 Nuclear Science Road, 3575 TAMU College Station, TX 77843-3575 November 10, 2016 2016-0057 Docket Number 50-59 / License No. R-23 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Ref: 10 CFR 50.90
SUBJECT:
Final Status Survey Plan Revision 1 for the Unrestricted Release of the Zachry Engineering Center Attn: Mr. Alexander Adams Jr., Chief, Mr. Patrick M. Boyle, Project Manager, Research and Test Reactors Branch Research and Test Reactors Branch Office of Nuclear Reactor Regulation Office of Nuclear Reactor Regulation The purpose of this letter is to submit Revision 1 of the Final Status Survey (FSS) plan for the unrestricted release of the Zachry Engineering Center. Texas A&M University (TAMU) submitted the original FSS plan on October 18, 2016 (NRC ADAMS Accession No. ML16299A537). Revision 1 of the FSS is being submitting to provide additional radiological information obtained during recent (October 2016) removal of the AGN-201M reactor and associated operational work in the Zachry Engineering Center, which supports the rationale for the proposed FSS plan methodology. TAMU will next be submitting a license amendment request (LAR) that will request the U.S. Nuclear Regulatory Commission (NRC) approval of the unrestricted release of the Zachry Engineering Center. The LAR is in its final review stages and TAMU anticipates submitting the LAR to the NRC soon. This FSS plan will also be an enclosure to the upcoming LAR.
Should you have any questions regarding the information provided in this submittal, please contact me or Mr. Jerry Newhouse at (979) 845-7551 or via email at mcdeavitt@tamu.edu or newhouse@tamu.edu.
Nuclear Science Center 1095 Nuclear Science Road, 3575 TAMU College Station, TX 77843-3575 Tel. (979) 845-7551 2
NUCLEAR SCIENCE CENTER Oath of Affirmation I declare under penalty of perjury that the foregoing is true and correct to the best of my knowledge.
Sincerely, Sean M. McDeavitt, PhD Director, TEES Nuclear Science Center Submitted with Level 2 Delegate Authorization from Dr. Yassin Hassan in letter dated February 8, 2016 (ADAMS Accession No. ML16043A048)
Enclosure:
FSS Survey Plan for the Unrestricted Release of the Zachry Engineering Center CC: next page
Nuclear Science Center 1095 Nuclear Science Road, 3575 TAMU College Station, TX 77843-3575 Tel. (979) 845-7551 3
NUCLEAR SCIENCE CENTER cc:
Mr. William Dean, Office Director United States Nuclear Reactor Commission Office of Nuclear Reactor Regulation Mr. Michael Young, President Texas A&M University 1246 TAMU College Station, TX 77843-1246 Dr. M. Katherine Banks, Vice Chancellor and Dean Dwight Look College of Engineering 3126 TAMU College Station, TX 77843-3126 Dr. Yassin Hassan, Department Head Nuclear Engineering Texas A&M University Nuclear Engineering Department 3133 TAMU College Station, TX 77843-3133 Dr. John Hardy Reactor Safety Board Chairman Texas A&M University 3255 TAMU College Station, TX 77843-3255 Dr. Latha Vasudevan Radiological Safety Officer Texas A&M University Environmental Health and Safety 1111 Research Parkway College Station, TX 77843-4472 Mr. Jerry Newhouse, NSC Assistant Director Texas A&M Engineering Experiment Station 3575 TAMU College Station, TX 77843-3575 Mr. Scott Miller, NSC Manager of Reactor Operations Texas A&M Engineering Experiment Station 3575 TAMU College Station, TX 77843-3575 Mr. Jeremy Osborn AGN-201M Reactor Supervisor Texas A&M University Nuclear Engineering Department 3133 TAMU College Station, TX 77843-3133
Nuclear Science Center 1095 Nuclear Science Road, 3575 TAMU College Station, TX 77843-3575 Tel. (979) 845-7551 4
NUCLEAR SCIENCE CENTER ENCLOSURE TEXAS A&M UNIVERSITY FACILITY LICENSE R-23, DOCKET NO. 50-59 AMENDED FACILITY OPERATING LICENSE AGN-201M REACTOR REVISION 1 FINAL STATUS SURVEY PLAN FOR THE UNRESTRICTED RELEASE OF THE ZACHRY ENGINEERING CENTER
SURVEYPLANFORTHE UNRESTRICTEDRADIOLOGICALRELEASEOFTHE AGN201MRESEARCHREACTORFACILITY ZACHRYENGINEERINGCENTER TEXASA&MUNIVERSITY COLLEGESTATION,TEXAS
Revision1 November10,2016
Contents ACRONYMS,ABBREVIATIONS,ANDUNITS...........................................................................................1
1.0 INTRODUCTION
.......................................................................................................................2 2.0 PURPOSEANDSCOPE.............................................................................................................3 3.0 SITEDESCRIPTION...................................................................................................................3 4.0 RADIONUCLIDECONTAMINANTSANDCRITERIA...................................................................9 5.0 IMPACTEDAREASANDSURVEYUNITS................................................................................13 6.0 SURVEYAPPROACH.......................................................................................................................14 6.1 General...........................................................................................................................14 6.2 SitePreparation.................................................................................................................15 6.3 IntegratedSurveyStrategy...............................................................................................15 6.4 FSSSurveyInstrumentation..............................................................................................17 6.5 SurfaceScans..................................................................................................................18 6.6 StaticSurfaceActivityMeasurements............................................................................19 6.7 RemovableContaminationMeasurements...................................................................19 6.8 SamplesandAnalyses....................................................................................................19 6.9 QualityAssurance/QualityControl...................................................................................19 7.0 DATAEVALUATION...............................................................................................................19 8.0 ISOLATIONANDCONTROL.20 9.0 REPORT20
10.0 REFERENCES
.......................................................................................................................20 APPENDIXA...................................................................................................................................A1 APPENDIXB...................................................................................................................................B1
1
ACRONYMS,ABBREVIATIONS,ANDUNITS
C carbon cm centimeter cm2 squarecentimeter cpm countsperminute Cs cesium dpm disintegrationsperminute Eu europium 3H tritium hr hour keV kiloelectronvolt m
meter m2 squaremeter MARSSIM MultiAgencyRadiationSurveyandSiteInvestigation Manual MDC minimumdetectableconcentration MDCR minimumdetectablecountrate MeV millionelectronvolts NRC NuclearRegulatoryCommission pCi picocurie pCi/g picocuriepergram PuBe plutoniumberyllium(neutronsource)
RSSI RadiationSiteSurveyandInvestigation TAMU TexasA&MUniversity TDSHS TexasDepartmentofStateHealthServices U
uranium Ci microcurie
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UNRESTRICTEDRADIOLOGICALRELEASESURVEYPLAN AGN201MRESEARCHREACTORFACILITY ZACHRYENGINEERINGCENTER TEXASA&MUNIVERSITY,COLLEGESTATION,TX
1.0 INTRODUCTION
TexasA&MUniversity(TAMU)isrenovatingtheZachryEngineeringCenter.ThisCenterhoused the AGN201Mreactor,licensedbytheNuclearRegulatoryCommission(FacilityLicenseR23).Italso containedofficesandlaboratoriesinwhichradiologicalmaterialswereusedinsupportofreactor operationsandotheractivities,asauthorizedunderTexasDepartmentofStateHealthServices (TDSHS)licenseL00448.Furnishings,materialsandequipmentweresurveyedandremovedfrom theStatelicensed areasofthefacility.Buildingsurfacesinthosenonreactorareasweresurveyed and demonstratedtosatisfytheTAMUcriterionfordemolitionwithoutneedfor radiological restrictions.Theseareashavebeenrazedinpreparationforrenovation.
Thereactorandassociatedcomponentshavebeenpackagedandplacedinsecureoffsitestorage, awaitingreinstallationinanewfacility(notethatthePart50licenseisnotbeing terminated).
Remainingmaterialsandequipmentinthereactorfacilityhavebeen surveyed,removed,and dispositioned inaccordancewiththe TAMUcriteria. Radiological surveys performed over the operatinghistoryoftheAGN201MreactorhaveidentifiednocontaminationoverTAMUrelease limitsinthereactorareasofZachryEngineeringCenter.Inaddition,recentsurveysconducted duringreactordisassemblyandinsupportoftheremoval,packagingandtransportofthereactor fuelandSNMhavenotidentifiedcontaminationoverTAMUreleaselimitsonthereactorexternal surfacesoronreactorinternalcomponentsurfaces(e.g.,inthecoretank,oncontrolroddrive thimblesthatpassthroughtheuncladfueldisks,andonthelowercoreplate).
ReNukeServices,Inc.,ofOakRidge,TN,hasbeencontractedbyTAMUtoremoveandrelocatethe reactor,developasurveyplan,andconductunrestrictedreleasesurveysofthebuilding.Thefinal resultswillbesubmittedasasupplementtoalicenseamendmentrequestfortheunrestricted releaseoftheZachryEngineeringCenter.
Office furnishings, miscellaneous materials and nonreactor equipment have been surveyed in accordance with the TAMU Radiological Safety Program and removed from the facility. No contaminateditemswereidentified.Screeningsurveys ofthereactorfacilitysurfaceshavebeen performed,withnocontaminationdetectedandnoneedfordecontaminationidentified.Based upon reactor power history and neutron surveys during power operation, activation of the buildingstructureisconsideredveryunlikely.Concretesamplesfromshieldblocksaroundthe reactor support skirt and from walls in the reactor room have been analyzed by an offsite laboratory for the presence of neutron activation products, and support this assessment; no activation products were detected. Based upon these surveys, the AGN201M design
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characteristics,andthefacilityhistoricaluses,theareashavebeenclassifiedastocontamination potential.Radiologicalsurveysoftheimpacted areaswillbeconductedtodemonstratethatthe facility conditions satisfy requirements for unrestricted future use and thus enable building renovationstoproceedwithoutradiologicalsafetyconstraints.
2.0 PURPOSEANDSCOPE
ThepurposeofthereleasesurveysistodemonstratethatareasoftheTexasA&MUniversity ZachryEngineeringCenter,whichhousestheAGN201Mreactorfacility,satisfycriteriaofthe Nuclear Regulatory Commission, Texas Department of State Health Services, and Texas A&M University Radiological Safety, Environmental Health and Safety for unrestricted release. By satisfyingthesecriteria,theremainingstructurecanbedemolishedorreusedwithoutradiological restrictions.
TexasA&MUniversitywillcomplywiththerequirementsof10CFR20.1402,radiologicalcriteria fortheunrestrictedreleaseoftheZachryEngineeringCenter.Inaccordancewiththisrule,thesite will be considered acceptable for unrestricted use if the residual radioactivity that is distinguishablefrombackgroundradiationresultsinatotaleffectivedoseequivalent(TEDE)toan averagememberofthepublicdoesnotexceed25mrem(0.25mSv)peryear.Nocontamination hasbeendetectedonanysurfacesorcomponentsduringextensivesurveysconductedinsupport ofdefuelingandduringearlierscopingsurveys,andTAMUcommitstousingthedefaultscreening valuesforsurfacecontaminationaspresentedinAppendixHtoNUREG1757,Volume2,Revision 1asupperlimitsfortheproject.Sitecharacteristicssupporttheuseofthesevalues,asonly superficial surface contamination is expected. There are no buried pipes or potentially contaminatedstructures,andnounusualradionuclidesareanticipated.Thescreeningvalueshave been determined by the NRC to be ALARA; no further pathways evaluations are required (AppendixNtoNUREG-1757,Volume2).TAMUsselfimposedreleasecriteriaaremorelimiting (contamination is not to exceed twice background, using appropriate instrumentation), as explainedbelow.
3.0 SITEDESCRIPTION
Figure1isasitemapoftheTexasA&Mcampus,indicatingthelocationoftheZachry Engineering Center,onBizzellStreetnearUniversityDrive. This Centerwashometo EngineeringStudent ServicesandAcademicProgramsOffice,aswellastheDepartmentof NuclearEngineeringandthe DepartmentofElectricalandComputerEngineering.Thebuilding isalargeconcretestructureand consistsofabasementlevel,agroundlevel,andthree additionalfloors. AsdepictedinFigure3, theAGN201MreactorwaslocatedinRoom61Bonthe groundfloor,inthesouthwestportionof thebuilding. Itisafullyselfcontainedunit,withno externalcoolantorirradiationsystems.The reactorcoreisarightcylinder,approximately26cmdiameterby24cmhighconsistingofninefuel discsandfueledcontrolrodscontainingnominally665gramsofU235atanenrichmentofjustless than20%.ThefuelisamixtureofUO2microspheresina polyethylenematrix. Thecoreandthe controlandsafetyrodsaresurroundedbyaleaktight, 95cmdiameterby148cmhighcoretank.
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A10cmthickleadshieldsurroundsthecoretank and20cmthickgraphitereflectors. A198cm diameterby213cmheightwatershieldtanksurroundsthereactorcoreassembly(Figure2). The maximumauthorizedsteadystate operatingpowerlevelis5watts,thermal.Thereactorhasnot operated for several years. The design of the AGN201M reactor precludes the possibility of groundwaterorsoilcontamination,astherearenoexternalcoolantpumps,heatexchangers,or coolantmakeup/cleanupsystems,andnoexternalirradiationloops.Inaddition,thebasicdesign precludestheneedforradioactivewasteprocessingsystems(e.g.,nowastecompaction,liquid waste treatment, or contaminated off gas treatment systems). Accordingly, the FSS does not addresssoilorgroundwatersampling.
Room60Cwasprimarilyusedforofficespaceandaccesscontrol.Room61Awasusedinsupport of reactor operations (e.g., safeguards laboratory work, experiment preparation). Room 61B contains the reactor control console and a small inner room where radioactive sources were stored.AccesstothetopofthereactoristhroughRoom135onthe1stfloorlevel,directlyabove thereactorroom.Rooms60C,61A,61B,and135(whichalsopreviouslycontainedanionimplant particleaccelerator)constitutetheprimarysitesecurityboundariesforthereactor.Theserooms occupy approximately 170 m2 on each level. They have 1m reinforced concrete walls; the acceleratorroomceilingisalso1mthickconcreteandasteelplateliner.Figures3and4showthe layoutsofthereactorfacility;boldedoutlinesindicatePrimaryReactorSiteboundaries.
ApolyethylenetankwaslocatedintheBasementdirectlybeneaththeprimaryreactorfacilityand wasconnectedtoafloordraininRoom61Btoallowcollectionofwaterintheunlikelyeventof leakage from the reactor shield tank (radiologically uncontaminated chromated water). This capabilitywasnotused,andthetankremainedemptyuntilitssurveyandremoval.ThesinglePVC drainlinedidnotcontaindetectableradioactivitywhenexaminedduringscopingsurveys.Itwas removedandallsectionssurveyed,alongwiththepolyethylenetank.Rooms135and61Awere alsoequippedwithsinkdrainspreviouslyconnectedtoasumpintheStatelicensedareaofthe building.Nocontaminationwasdetectedintheglassdrainlineortheinlinetrapinthereactor areas,andnocontaminationwasidentifiedduringsamplingofthesumportheStatelicensed laboratorydrains.Thesedrainswereterminatedandthesumpreleasedaspartofthelaboratory decommissioning.
ThefacilityshareselectricpowerandairsupplywiththeremainderofZachryEngineeringCenter building. During normal power operation, ventilation for the reactor area was provided by a ventilationfaninRoom135,which pulledairthroughagratedopeningintheRoom61Bceiling.
Portionsoftheventilationsystem weresurveyedinearly2016duringlaboratoryfacilitysurveys, andfoundtomeetthe applicablereleasecriteria.
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Figure1-MapofTexasA&MCampus,indicatinglocationofZachryEngineering
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Figure2-CutawayViewofAGN201MReactor
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Figure2a-AGN201MReactorwithoutblockshielding,ascurrentlylocatedinZachry EngineeringCenter
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Figure3ReactorFacilityGroundFloor;BoldedoutlineindicatesSecurityBoundary
Figure4-ReactorFacilityFirstFloor;BoldedoutlineindicatesprimaryReactorSite Boundary
Sampled block wall
48 ---------------------------
27 -------------
27 ------------
48 --------------------
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4.0 RADIONUCLIDECONTAMINANTSANDCRITERIA
AGN201MreactoroperationsintheZachryEngineeringCenterbeganin1972andconcludedin 2014. Duringtheschoolyearsof1999/2000through2009/2010,thereactorwasnotoperated.
Inotheryears,annualoperatingwatthoursrangedfrom4.32to82.36. Sincethe2009/2010 schoolyear,thetotaloperatingtimehasbeenapproximately138watthours.Therehasbeenno reactoroperationsince2014.RecordsandanecdotalinformationfromthepreviousSeniorReactor Operatorhave not revealedanyreactorincidentsoroccurrenceswhichmayhaveresultedin contaminationof surfacesexternaltothereactorshieldtank. Resultsofsurveysperformedby theTAMURadiologicalSafetystaffdidnotidentifyanydetectableremovablecontaminationon reactorcomponentsorreactor roomsurfaces.Recentscopingsurveysdidnotdetectanyfixed orremovablecontaminationonsurfacesinrooms61Aand61B. Consideringthelowpowerlevel andlimitedoperatingtime,low neutronfluencerate(1.5x108n/cm2sec,averageatthe5watts maximum licensed power), inherent shielding provided by the reactor components and containmenttank,andthedecaytimesince lastoperation,thelikelihoodofdetectableactivity infacilitystructuralmediaisconsideredtobenegligible.
Conservative,boundingcalculationsestimate152Eu(likelythepredominantactivationproductin concrete)specificactivityintherangeof103pCi/ginconcreteshieldblocksthatwerelocated around the reactor support skirt. Sampling and analyses was conducted to validate the calculationbased conclusion that no activation products are present at detectable levels.
Candidate radionuclides for concrete activation include 152Eu, 154Eu, 60Co, 134Cs, 3H, and 14C.
Laboratoryanalyses(gammaspectrometryandliquidscintillationcounting)ofcoresamplesare summarizedbelow.Samplesincludedcoresfrom4innermostshieldblockspreviouslyaroundthe reactorskirt(shieldingsubjecttothehighestneutrondose),1corefromtheNorthroomwall, collecteddirectlyacrossfromthegloryhole,3coresfromtheSouthblockwallinlinewiththe gloryhole,2coresfromthenominal31/2concretereactorpad,2coresfromtheconcretefloor directlyunderthereactorpad,and1corefromthewallintheaccesshallway,anareawithno significantneutronexposure.Noneofthesampleswerefoundtocontaindetectableactivation products,withminimumdetectableconcentrationsfortheradionuclidesofinterestlessthan10%
oftheNUREG1757soilscreeningvalues.EuropiumMDCswerealso<10%oftheEPAvaluesfor residentialsoils.ThesescreeningvaluesaredirectlyapplicableasaportionoftheSouthwallwas openedforremovalofthereactorshieldtank.Exposureratesurveys1meteroverthereactorpad werenotdifferentthanthenominal5microR/hambientexposureratesthroughoutthefacility.
SampleresultsarepresentedinTable1.
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Table1.
Volumetricsampledata
134Cs 60C 152Eu 154Eu 3H 14C Noactivationproductsdetected MDC, pCi/g MDC, pCi/g MDC, pCi/g MDC, pCi/g MDC, pCi/g MDC, pCi/g Wall:hallway(noneutronirradiation) 5.82E02 7.23E02 1.12E01 1.73E01 5.43E+00 1.41E+00 Wall:Nside,oppositegloryhole 8.97E02 9.91E02 1.90E01 2.97E01 5.44E+00 1.37E+00 S.Wall1:IW1(wallremoved) 4.77E02 4.30E02 1.09E01 1.01E01 7.63E+00 6.26E01 S.Wall2:IW2(wallremoved) 4.52E02 4.11E02 1.40E01 1.30E01 7.85E+00 6.01E02 S.Wall3:IW3(wallremoved) 7.01E02 6.72E02 1.29E01 2.26E01 8.08E+00 6.21E01 Reactorshieldblock:E1 7.87E02 7.69E02 1.31E01 2.17E01 7.96E+00 5.98E01 Reactorshieldblock:S1 8.06E02 7.64E02 1.70E01 1.86E01 8.07E+00 6.14E01 Reactorshieldblock:N1 5.54E02 7.87E02 1.64E01 1.99E01 7.88E+00 6.07E01 Reactorshieldblock:W1 6.01E02 5.80E02 1.30E01 1.84E01 8.06E+00 1.00E+00 Reactorpadconcrete1 5.89E02 5.19E02 1.26E01 1.55E01 6.85E+00 6.34E01 Reactorpadconcrete2 5.59E02 5.20E02 1.14E01 1.41E01 6.30E+00 6.35E01 Floorunderreactorpad,1 9.17E02 6.72E02 1.77E01 2.07E01 6.27E+00 6.51E01 Floorunderreactorpad,2 6.87E02 5.17E02 1.69E01 1.98E01 6.58E+00 6.30E01
SouthWall(IW1toIW3)
ShieldBlockWall(4Samples)
ReactorPadConcrete(4samples)
Coveringshavenotbeen appliedoveranyknownlocationofcontamination. Thelocationinthe facilityconsideredmost likelytohavebeenimpactedbyreactoroperationsistheconcretefloor directlybeneaththe reactorshieldtank. Potentialactivationradionuclidesincludethe same radionuclidesintheabovetable.Thecoreassemblycontainsenricheduraniumfueland(likely) verysmallquantitiesof longerhalflifefissionproductsincluding 137Cs,90Sr,144Ce,and 95Zrand activation productssuchas60Coincomponents;however,thereisnohistoryofcontaminationby theseradionuclidesonsurfacesexternaltothereactor.
TheNRCreactorlicenseincludesa239PuBespecialformneutronsourcecontainingupto16grams of239Puforuseinreactoroperation.Thissourcewasleaktested(nocontaminationwasdetected),
removedfromtheAGN201Mreactor,andtransportedtooffsitestorage
Section 17.1.4 of NUREG1537 establishes the following criteria to release nonpower reactor facilitiesforunrestricteduse
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- 1. a)nomorethan5microremperhourabovebackgroundat1meterfromthesurface measured for indoor gamma radiation fields from concrete, components, and structures,or
b)nomorethan10milliremperyearforgammaemittersabovebackgroundabsorbed dosetoanyperson,consideringreasonableoccupancyandproximity(NRCletters dated March17,1981andApril21,1982).
- 2. residualsurfacecontaminationconsistentwithRegulatoryGuide1.86.
Regulatory Guide 1.86 was withdrawn by NRC, effective August 12, 2016, although similarnumericalguidanceremainsinRegulatoryGuides8.21,HealthPhysicsSurveys forByproductMaterialatNRCLicensedProcessingandManufacturingPlants,and8.30, Health Physics Surveys in Uranium Recovery Facilities. The table of surface contaminationvalueshasbeenretained(seeTable2)fortheprojectasthesevaluesare alsoinTexasRegulation25TAC§289.202(ggg)(6),Acceptablesurfacecontamination levels(Ref2),andareapplicabletoStatelicensedactivitiesatTAMU.
Table2.
AcceptableSurfaceContaminationLevelsbasedonDetectability Nuclidea Total Removable Unat,U235,U238,andassociateddecay products 5000 dpm/100 cm2 1000dpm/100 cm2 Transuranics,Ra226,Ra228,Th230,Pa231,Ac227, I125,I129 100dpm/100cm2 20dpm/100cm2 Thnat,Th232,Sr90,Ra223,Ra224,U232,I126,I 131,I133 1000dpm/100cm2 200dpm/100cm2 Betagammaemitters(nuclideswithdecaymodes otherthanalphaemissionorspontaneousfission) exceptSr90andothersnotedabove 5000dpm/100cm2 1000dpm/100cm2 a.Wheresurfacecontaminationbybothalphaandbetagammaemittingradionuclidesexist,thelimits establishedforalphaandbetagammaemittingradionuclidesapplyindependently.
TheTAMUradiationsafetyprogramhasapolicyofnodetectableactivityfor unrestricteduse and release. No detectable activity is interpreted by TAMU as not exceeding twice the backgroundlevel(Ref1).
DuetootherZachryEngineeringCenterrenovationworkstartingpriortothereactorrelocation project,suitableconcretesurfacesoutsidethereactorcomplexwerenotavailableforreference backgroundmeasurements.BackgroundmeasurementswereperformedinaClass3area(Room 60C)onasectionofpouredconcretefloorunlikelytohavebeenimpactedbyreactoroperations.
Thisarea,aswiththeotherfloorareas,wascoveredwithfloortilesincethestartofreactor operations.Thetilehassincebeenremovedfromallareas.Thepouredconcretebackground levelsforthe126cm2gasflowproportionaldetectorsareeffectivelytheobservedambientbackground levels of 3 alpha cpm and 250 beta cpm. As expected, the larger (nominally 580 cm2) gasflow proportionalfloormonitorexhibitshigherambientbackgroundlevelsofapproximately9alphacpmand
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300betacpm.Initialsurveyworksupportstheconservativeuseofambientbackgroundlevelsfor scanningsurveysofthefloorsandtheremainderofthefacilitysurfaces(primarilypouredconcrete walls,steelandglass).Theambientbackgroundvalueswillalsobeconservativelyappliedtosurveys oftwohigherdensityblockshieldwallsinRoom61B.Laboratoryanalysisdemonstratesahigher concentrationofthe232Thseriesradionuclidesrelativetootherblockandconcreteusedinfacility construction,andtheimpactonsurveysisanincreasedbackgroundcountrateof100cpmonthese blocks.Thismaterialspecificbackgroundwillnot,however,beapplied.Theambientbackground will also be used for scanning surveys of these walls. To summarize, no materialsspecific backgroundcountrateswillbesubtractedfromscanningsurveysoffacilitysurfaces.Notethat2 stepsurveyswillbeusedforstaticmeasurements,asdescribedinsection6.3,IntegratedSurvey Strategy.
The nominal ambient background values are used to calculate the sensitivity of the scanning surveys to ensure they are adequate relative to the surface contamination Screening Values presentedNUREG1757,AppendixH.Becausenoresidualradioactivityhasbeenidentifiedduring extensivesurveysofthereactor,associatedcomponents,andthefacility,nospecificradionuclides ofinteresthavebeenidentified.TheNUREG1757,AppendixHsurfacecontaminationscreening valuefor 60Co(7,100dpm/100cm2)hasbeenconservativelychosenforevaluationofpotential building contamination. Table 3 presents a summary of the minimum detectable surface contamination,theNRCscreeningvalue,andthesurfacecontaminationlevelscorrespondingto twicethebackgroundlevels(theTAMUconstraint).
Duringscanningsurveys,netcountratesexceeding450cpmbetawhenusingthe126cm2detectors, or800cpmbetaforthe580cm2 detector, willbeindicativeof contaminationexceedingthe screeningvaluefor60Co.
Theassumptionthattheremovableactivityfractiondoesnotexceed10%willbeevaluatedif contaminated areas are identified. Table 3 clearly demonstrates that meeting the TAMU Radiological Safety criteria for release will also satisfy the NRC requirements. As noted, no contamination has been detected and no specific radionuclides have been identified during extensivescopingsurveys; 60Cohasbeenconservativelyselectedasapossibleradionuclideof concern.Grossalphaandbetagammasurveyslimitswillbeapplied(i.e.,nottoexceedtwice background,alphaandbetagammaactivityevaluatedindependently).Alsonotethatnetcount ratesexceeding3cpmalphaor250cpmbetawhenusingthe126cm2detectors,or9cpmalphaor 300cpmbetaforthe580cm2detector,willbeindicativeof contaminationexceedingtheTAMU criteria(twicebackground)andwillrequirefurtherinvestigation.
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Table3.
SummaryData Detector/Application MDA (dpm/100 cm2)
NRC Co-60 Default Screening Value (dpm/100 cm2)
TAMU twice background equivalent (net dpm/100 cm2) 126 cm2 gas proportional/scan Alpha - N/A
- 1500 beta Alpha - N/A*
7100 N/A 3000 126 cm2 gas proportional/static 63 alpha 470 beta Alpha - N/A*
7100 26 alpha (< MDC) 2200 beta 580 cm2 gas proportional/scan Alpha - N/A*
2280 beta (for a 100 cm2 spot)
Alpha - N/A*
7100 A > 2 x background reading will be investigated with a 126 cm2 detector Laboratory counter/removable activity 19 alpha 90 beta Alpha - N/A*
710 4 alpha 500 beta
- No potential alpha-emitting contaminants have been identified
MeasuredbackgroundexposurerateswithintheZachryEngineeringCenterare5to8microR/hr.
TheTAMUlessthantwicebackgroundcriterionwill bemetby confirmingthatdoseratesfrom backgroundplusresiduallicensedmaterialarenomorethan10microR/h,measuredat1meter frombuildingsurfaces.Thisisconsistentwiththepreviouslynoted guidancefromNUREG1537.
5.0 IMPACTEDAREASANDSURVEYUNITS
The MultiAgency Radiation Survey and Site Investigation Manual (MARSSIM) (Ref 3) defines impactedareasasthosewithapossibilityofresidualradioactivityinexcessofbackground levels.
Radiologicalsurveysofimpactedareasarerequiredtodemonstratethatestablished criteriahave been satisfied. Nonimpacted areas are those with no reasonable expectation of residual contamination;nosurveysofnonimpactedareasare required. Impactedareasareclassifiedas tocontaminationpotentialasfollows:
Class1: Areasthathave,orhadpriortoremediation,apotentialforradioactive contamination(basedonsiteoperatinghistory)orknowncontamination(basedon radiologicalsurveys)expectedtobeinexcessofestablishedunrestrictedrelease criteria.
Class2: Areasthathave,orhadpriortoremediation,apotentialforradioactive contaminationorknowncontamination,butarenotexpectedtoexceedestablished criteria.
Class3:Areasthatarepotentiallyimpactedbutarenotexpectedtocontain any residualradioactivity,orareexpectedtocontainlevelsofresidualactivityatasmall fraction oftheestablished criteria,basedonsiteoperatinghistoryandprevious radiologicalsurveys.
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Therigorofareleasesurveyisbasedonthesecontaminationpotentialclassifications.Structure surveyunitsareestablishedwithsizelimitationspresentedinTable4.
Table4.
SurveyUnitAreabyClassification Classification MaximumArea(m2)
Class1 100 (floor surface)
Class2 100 to 1000 Class3 No limit
Table5containsapreliminarylistofAGN201Mreactorfacilityimpactedareasandsurvey units.
Thislistisbasedonusehistoryandpreviousmonitoringrecords.Screeningsurveys, conducted during removal of furnishings, materials, and equipment from the facility support the recommendedclassifications.
Table5.
ImpactedAreasandSurveyUnits
Class
Level
Room(s)
Surfaces
Numberof SurveyUnits
Class1
Ground
61A
Floorandlowerwalls
1
Ground
61B
Floorandlowerwalls
1
First
135
Floorandlowerwalls
2
Class2
Ground
61Aand61B
Upperwallsandceiling
1
Class2
First
135
Upperwallsandceiling
1
Class3
Ground
60C
All
1
6.0 SURVEYAPPROACH
6.1 General Thissurveyplanwaspreparedinaccordancewithguidelinesandrecommendations,presented in theMultiAgencyRadiationSurveyandSiteInvestigationManual. Theprocessdescribedin this reference emphasizes and incorporates the useof Data Quality Objectives and Data Quality Assessment,alongwithaqualityassurance/qualitycontrolprogram. Aqualityassuranceprogram forsurveyactivitieswillbeimplemented. Thegradedapproachis followedtoassurethatsurvey effortsaremaximizedinthoseareashavingthegreatest potentialforresidualcontaminationor thehighestpotentialforadverseimpactsofresidual contamination.
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Trainedandqualifiedradiologicaltechnicianswillconductfieldmeasurements,followingstandard procedures and using calibrated instruments, sensitive to the potential contaminants.
Professionalhealthphysicspersonnelwillassessandevaluatethesurveydataandpreparea reportofthefindings.
6.2 SitePreparation Furnishings,materialsandequipmenthavebeenremovedfromthefacilityinaccordancewith TAMURadiationSafetyProgramprocedures.Followingremovalandtransferofthereactorand associated components, drains, ducts, diffusers, grates, cable trays, etc., were accessed and surveyed. Nominal100cm2dualphosphordetectors(LudlumInstrumentsModel4393)have been used with dual channel scaler/ratemeters (Ludlum Instruments Model 2360) for health physicssurveysconductedinsupportofdefuelingandcleanupwork.Notethatbackgroundand efficienciesforthesescintillationdetectorsareidenticaltothegasflowproportionaldetectors selectedforfinalstatussurveys.Useofthemodel4393scintillationdetectorswasaugmented with thinwindow pancake GeigerMueller detectors with scaler/ratemeters (Ludlum InstrumentsModel439detectorswithModel3scaler/ratemeters)toaccesssmallerdiameter penetrations(e.g.,usedforelectriccables,watersupplylines,naturalgaslines,etc).Todate,no buildingsurfaceshavebeenfoundtocontaindetectableresidual activity,withMDCswellbelow theNRCandTAMUreleasecriteriaaspresentedinTable2andnoremediationhasbeenrequired.
Buildingsurfaceshavebeenappropriately griddedtoprovideameansforreferencingsurvey locations. Measurementswillbeidentifiedbygridcoordinateor,ifnotpractical,byreferencingto buildingfeaturesorbyphotograph. Surfaceswherecontaminationwasdeemedlikely(Class1)or possible(Class2)havebeengriddedat1meter intervals,asispracticalfortheconditions. Grid originsareinthesouthwestcorneroftheroom. If,duringthesurvey, contaminationabovelimits isidentifiedinClass2orClass3areas,therigorofthesurveyunitwillbeincreased tothatofClass 1areas.
6.3 IntegratedSurveyStrategy
Radiologicalsurveyswillconsistof:
surfacescansforelevatedlevelsofgrossalpha,beta,andgammaradiationlevels, staticmeasurementsofgrossalphaandgrossbetaactivity, smearsforremovablegrossalphaandgrossbetaactivity,and samplingforlaboratoryanalysisofspecificradionuclidecontaminants,ifnetactivityis found
Baseduponfacilityhistoryandsurveysperformedinsupportofreactordisassemblyandremoval oftheshieldtank,therigorofsurveyswillfollowagradedapproachbasedonthelikelihoodof contamination. Table6indicatesthesurveyrigorforvariouscontaminationclassifications.
16
Table6.
SurveyRigorforEachSurveyUnit Contamination Class Alpha,Beta, andGamma Scan StaticAlphaandBeta Removable Alphaand Beta 1
100%all structure surfaces Systematic static measurement at a minimum of 18 locationsandatadditionallocationsofhighest potentialcontamination,basedonprofessional judgmentandscanresults Ateachstatic measurement location 2
50%floorand lowerwalls; 10%upperwalls andceiling surfaces Systematicstaticmeasurementataminimumof18 locationsandatadditionallocationsofhighest potentialcontamination,basedonprofessional judgmentandscanresults Ateachstatic measurement location 3
10%floor and1m2 aroundeach static measurement locationon lowerwalls Onefloormeasurementand1lowerwall measurementper10m2offloorareaineach room,andmeasurementsandatadditional locationsofpotentialcontamination,basedon professionaljudgmentandscanresults(minimum of18datapointspersurveyunit).
Ateachstatic measurement location
Becausetheacceptablereleasecriterionoftwicebackgroundislow,ScenarioB,as recommended byNUREG1505(Ref4),isthebasisforthesurveydesign.TheNullHypothesis forthatScenariois:
Thesurveyunitmeetsthereleasecriterion.
TheobjectiveofthereleasesurveyistoacceptthisNullHypotheses,bydemonstratingata TypeI
() decision error level of 0.05 and a Type II () decision error level of 0.025 that residual contaminationislessthantwicebackground. Therearemultiplebuildingsurfacetypes (concrete, metal,wood,glass,etc.)inmostsurveyunitsand,backgroundlevelswilllikelyvary, byinstrument, material,timeofday,andlocationwithinthefacility. Tofacilitateadjustingmeasurementsfor appropriatelocalizedbackgroundcontributions,apairedmeasurementapproach willbeused. To performpairedmeasurements,ameasurementisfirstperformedbyplacinga pieceofnominal1/4 inchplasticormetalshieldmaterial,betweenthesurfaceandtheLudlum4368detectorface. The static measurement is repeated without the intervening shield material, and the difference betweenthesecondandfirstmeasurementindicatesthenetcontaminationlevel.
Eachmeasurementwillbeindividuallyevaluatedandnoindividualmeasurementmay indicate detectableactivityinexcessoftheprojectlimits(e.g.,allnetmeasurementsmustbelessthanthe 3alphaand250 betacpmnominalcountratesasmeasuredwiththe4368detectorsthemore restrictiveTAMUlimits). Nostatisticaltestwillberequiredtodemonstratecompliance with releasecriteria.
Toestablishthenumberofmeasurementsneededtodemonstratethatresidualcontamination criteriahavebeensatisfied,aparameterknownastherelativeshift,whicheffectively describes thedistributionoffinalsampledata,iscalculated,asfollows:
17
(1) /=(DCGLLBGR)/
where:
/
= relativeshift DCGLCriteria= cleanupcriteria LBGR
= lowerboundofthegrayregionandisdefinedintheDQOsas50percent oftheDCGL. Wherefinalsampledataarenotyetavailable,MARSSIM guidance(Section5.5.2.2)assignsavalueofonehalfoftheDCGLforthe LBGR.
= standard deviation of the sample concentrations in the survey unit.
Where final sample data are not yet available, MARSSIM guidance (Section5.5.2.2)recommendsavalueof30percentoftheDCGL.
UsingtheequationforrelativeshiftandMARSSIMguidanceforsituationswherefinalsample data arenotyetavailable,therelativeshiftfordesignpurposesis(1-0.5)/0.3foravalueof1.67. Based ontherelativeshiftof1.67andTypeIandTypeIIdecisionerrorsof0.05and 0.025,respectively, thenumberofrequireddatapointsfromeachsurveyunittoperformthe evaluation,asobtained fromMARSSIMguidance(Table5.5)is18.
ForstaticmeasurementlocationsonClass1andClass2roomsurfaces,arandomstartpoint will beidentifiedonthefloorandadditionalmeasurementlocationswillbesystematically selectedon atriangularspacingfromthatstartpoint.Spacingdistance,L,isdeterminedby
L=[(SurveyUnitArea)/0.866xnumberofdatapoints]0.5
Internal surfacesofductwork and piping will be accessed, scanned, and static measurements performedattheentranceanddischargeandadditionalpointsatafrequencyof1 measurement per4m2ofinternalsurfacearea.
Static measurement locations on Class 3 room surfaces will be at locations of highest contaminationpotential,asselectedbyprofessionaljudgment.
6.4 FSSSurveyInstrumentation Table7isalistofradiologicalsurveyinstrumentationthatwillbeusedtoimplementtheAGN201M reactor facility surveys. These instruments will be maintained, calibrated, and operated in accordancewithwrittenprocedures.Forapplicationtounrestrictedrelease,instrument response (efficiency)isbasedonNIST-traceablesourcesofTc99(betaEMAX=292keV)andTh 230(alpha E=4.68MeV). Theenergiesoftheseradionuclidesarerepresentativeofthe dominantpotential contaminants.Notethatthe126cm24368gasflowproportionaldetectorshavedetectorefficiencies andambientbackgroundcountratesthatareidenticaltothe100cm24393dualphosphorscintillation detectorsusedforhealthphysicssurveysduringfacilitypreparationsforrelease;surveydataaredirectly comparable.
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Table7.
InstrumentationforReleaseSurveys Detector Display Application Ludlum4337 Ludlum2360 Alpha/betascans Ludlum4368 Ludlum2360 Alpha/betascans Ludlum4368 Ludlum2360 Alpha/betastaticmeasurements Ludlum4310 Ludlum2929 Removablealpha/betameasurements (scaler)
Ludlum19 N/A Gammascans/directgammameasurements
For field measurement applications, calibration represents 2 response. Effects of surface conditionsonmeasurementsareintegratedintotheoverallinstrumentresponsethroughuse ofa sourceefficiencyfactor,inaccordancewiththeguidanceinISO75031(Ref7)and NUREG/CR 1507(Ref8). Defaultsurfaceefficienciesof0.25foralphaemittersand0.25forbeta emitterswill beused.
Detection sensitivities are estimated using the guidance in MARSSIM and NUREG/CR1507.
Instrumentation and survey techniques are chosen with the objective of achieving detection sensitivities of <50% of the criteria for structure surfaces, for both scanning and direct measurement.Thesedetectionsensitivitiesassureidentificationofareaspotentiallyexceedingthe establishedproject criteria. Minimumdetectableactivitylevels(refertoAppendixA)forthis surveysatisfythe Table1values.
6.5 SurfaceScans Scans of surfaces will be performed to identify locations of potential residual surface contaminationandinducedactivity. Gasproportionaldetectorswillbeusedforalphaandbeta scans. ALudlumModel4337gasproportionaldetector(580cm2)willbeusedwitha Ludlum Model2360scaler/ratemetertoscanthefloorsurfaces. Surfacesnotaccessiblewith thislarge detector will be scanned with the smaller Ludlum Model 4368 gas proportional detectors (126cm2) used with Ludlum Model 2360 scaler/ratemeters. Alpha/beta scanning will be performedby maintainingthedetectorwithin1/4inchofthesurfaceandpassingthedetectorover thesurface atarateofapproximately1/2detectorwidthpersecond,whilemonitoringtheaudible outputof thescaler/ratemeterforimmediateidentificationofincreasesincountrate. When2 alpha countsaredetectedwithinapproximately2seconds,thedetectormovementwillbehalted atthelocationforapproximately10 secondstodetectapossibleelevatedcountrate.Thisis consistentwithAppendixJguidanceintheMARSSIMdocument(NUREG1575).
ALudlumModel19gammascintillationdetectorwillbeusedforgammascans. Generalarea gammamonitoringwillbeperformedwiththedetector approximately1mabovethefloor.
19
6.6 StaticSurfaceActivityMeasurements
StaticmeasurementofalphaandbetasurfaceactivitywillbeperformedusingLudlumModel 43 68gasproportionaldetectorswithLudlumModel2360scaler/ratemeters.Measurementswillbe conductedbyholdingthedetectorinpositionwithin1/4inchofthe surfaceandintegratingthe countovera2minuteperiod.Twomeasurements,1shieldedand1unshielded,willbeperformed ateachstaticmeasurementlocation,withthenetcountratebeingthedifferencebetweenthe twomeasurements,foralphaandbetadetection.
6.7 RemovableContaminationMeasurements
Asmearforremovableactivitywillbeperformedateachstaticsurfaceactivitymeasurement location. A100cm²surfaceareawillbewipedwithanominal2inchdiameterclothsmear,using moderatepressure.
6.8 SamplesandAnalyses
SmearswillbeanalyzedonsiteforgrossalphaandgrossbetaactivityusingaLudlumModel 2929 scalerwithaModel43101dualscintillationdetector(orequivalentinstrumentation).
6.9 QualityAssurance/QualityControl
Measurements will be performed in accordance with the survey plan by qualified personnel followingwritteninstrumentoperatingprocedures. InstrumentcalibrationpracticesmeetANSI standardsanddailybackgroundandsourceresponsechecksofinstrumentswillbeperformeddaily.
Forqualitycontrolpurposes,replicatestaticandremovableactivitymeasurementswere obtained at2locationsineachsurveyunit.
7.0 DATAEVALUATION
Surface contamination measurement data will be adjusted for background contributions and convertedtounitsofnetcountsperminute.Datawillbeassessedtoverifythatthetype, quantity, andqualityareconsistentwiththesurveyplananddesignassumptions.Individual datavalueswill becomparedwiththecountratelimitderivedfromNUREG1757surfacecontaminationscreening values for 60Co and the TAMU criteria of twice background. Residual contamination limits establishedfortheproject(seeSection4)arepresentedinTable3,includingacomparisonofthe TAMUlimitsandtheNRCscreeningvalues.
EvaluationofvolumetricsampledataisdiscussedinSection4,RadionuclideContaminantsand Criteria
20
8.0 ISOLATIONANDCONTROL Followingcompletionofthereleasesurvey,thefacilitywillbeisolatedandaccesscontrolled until NRCapprovalforunrestrictedreleaseisreceived. ItisrecognizedthattheNRCmay chooseto conduct independent surveys to confirm the findings of this survey. These areas will not be availableforgeneralaccessorworkuntilNRCapprovalforunrestrictedreleaseisobtained.
9.0 REPORT
Adraftreportdescribingthesurveyproceduresandfindingswillbeprepared. Thisreportwill standaloneandprovideacompleterecord,documentingthefacilitysradiologicalstatus satisfies established project criteria and that the facility is therefore ready for unrestricted release.
AppendixB isasampleofthereportcontent. Thereportwillincludeallsampledatasupporting this determination.Commentsonthedraftreportwillberesolvedandafinalreportpreparedand submittedtotheNRCforreviewandapproval.
10.0 REFERENCES
- 1. RadiologicalSafetyProgramManual,RadiologicalSafetyEnvironmentalHealthand Safety Department,TexasA&MUniversity,July2004.
- 2. Texas Regulations for acceptable contamination levels for unrestricted use, 25 TAC§289.202(ggg)(6).
- 3. MultiAgencyRadiationSurveyandSiteInvestigationManual(MARSSIM),NUREG1575 (Rev.
1),U.S.NuclearRegulatoryCommission,2000.
- 4. A Nonparametric Statistical Methodology for the Design and Analysis of Final Status DecommissioningSurveys,NUREG1505(Rev1)U.S.NuclearRegulatoryCommission, 1998.
- 5. EvaluationofSurfaceContamination-Part1:BetaEmittersandAlphaEmitters,ISO 75031, InternationalOrganizationforStandardization,1988.
- 6. MinimumDetectableConcentrationswithTypicalRadiationSurveyInstruments for Various ContaminantsandFieldConditions,NUREG/CR1507,U.S.NuclearRegulatory Commission, 1997.
- 7. ConsolidatedDecommissioningGuidanceCharacterization,Survey,and Determination of RadiologicalCriteria,NUREG1757,Vol.2,Rev.1,U.S.Nuclear RegulatoryCommission,2006.
A1
AppendixA
Measurement/DetectionSensitivitiesofSurveyTechniques
ThemethodsforcalculatingsurveydetectionsensitivitiesarepresentedinMARSSIM(Ref1)and NUREG1507(Ref2).Detectorparametersusedinthesecalculationarebackgroundcountrate, efficiency(instrumentresponseandsurfacecorrectionfactors),anddetectorarea.Thefollowing tablepresentstypicalvaluesoftheseparametersfordetectorsusedfor surveysofconcrete structuresurfacesoftheAGNreactorfacility.Backgroundlevelsforconcretearethehighestfor surfacemediaremaininginthisfacility,andthereforedirectmeasurementsonothermediawill bemoresensitivethanthosepresentedhereforconcrete.
Detector/
Instrument Probe Area (cm2)
Background(cpm)
Detectorefficiency Surfacecorrection
alpha beta alpha beta alpha beta 4337 580 9
300 0.50 0.46 0.25 0.25 4368 126 3
250 0.36 0.36 0.25 0.25 2929 N/A 1
25 0.25 0.20 N/A N/A
AlphaScans
SurfacescansforalphaactivityareconductedusingLudlumModel4337andModel4368gas proportional detectors, coupled with Ludlum Model 2360 scaler/ratemeters. MARSSIM recommendstheuseofPoissonsummationstatisticstoestimatetheprobabilityofdetectinga smallnumberofcountsthatmayindicatethepossiblepresenceofalphacontaminationduringa relativelyshortobservationperiod.Theequationforestimatingtheprobabilityofdetecting1or morecountsis:
P(n>1)=1-e[((GE+B)t))/60]
where:
P(n>1)=Probabilityofgetting1ormorecountsduringthetimeinterval G=Sourceactivity(disintegrationsperminute,dpm)
B=Backgroundcountrate(countsperminute,cpm)
E=Detectorefficiency(counts/disintegration) t=Dwelltimeoversource(sec)
Theprobabilityofdetecting2ormorecountsisgivenby:
P(n>2)=1-(e[((GE+B)t)]/60]-((GE+B)(t))/60).e[((GE+B)t)]/60]
Using these parameters, detection probability calculations for a contamination level of 100
A2
dpm/100cm2wereperformedforascanrateof1/2detectorwidthpersecond(i.e.,dwelltimesof 2seconds)Theprobabilitiesofdetectingasinglealphacountduringa2seconddwelltimeare approximately33%forthe4368detectorand52%forthe4337detector.Becauseofthehigher backgroundcountrateassociatedwiththe4337floormonitordetector,MARSSIM(AppendixI) recommendsusing2countsasascreeningvaluewhenscanningforalphacontamination.The probability of detecting 2 counts with the larger detector increases to approximately 82%.
Whenever a count is detected, the detector is paused over the surface for 10 seconds to determine whether there is actually elevated alpha activity present, in which case, a static measurementisthenperformed.A10secondpauseresultsina90%orgreaterprobabilityof identifyingthepresenceofalphaactivityexceeding100dpm/100cm2.Althoughthecalculated scandetectionprobabilitiesmayappearrelativelylow,itshouldbenotedthathistoricrecords andcharacterizationsurveyshavenotidentifiedanypotentialforalphacontaminationinthis facility.
AlphaActivityStaticMeasurements
Staticmeasurementsofalphasurfaceactivityareperformedusing4368detectors,withthesame background and response characteristics as indicated above for alpha scanning. A static measurementisperformedbyplacingthedetectoronthesurfaceandallowedtointegratethe countforaperiodof2minutes.Theminimumdetectablealphacontaminationlevel(MDC)is calculatedasfollows:
MDC=[3+4.65(BKGD)1/2]/(efficiencyfactors)(detectorarea/100)(counttime)
Theresultingvalueisapproximately63dpm/100cm2.
BetaScans
SurfacescansforbetaactivityareconductedusingLudlumModel4337andModel4368gas proportional detectors, coupled with Ludlum Model 2360 scaler/ratemeters. The detector is passedoverthesurfaceatarateof1/2detectorwidth/sec,whilemaintainingthedistancefrom thedetectortothesurfaceatapproximately0.5cm.Theaudiblesignalfromtheinstrumentis monitoredbythesurveyor.Detectablechangesinthecountratearenoted,andtheimmediate arearesurveyedatareducedspeedtoconfirmthechangeinaudiblesignaland,ifapplicable,to identifytheboundaryoftheimpactedarea.Theminimumdetectablecountrate(MDCR)isa functionofthebackgroundcountrate(BKGD)incountsperminute(cpm)andthetime(i)in secondsthatthedetectoriswithincloseproximitytothesourceofradiation.Equation66of NUREG1507providesthefollowingrelationship:
MDCR=d[BKGD*i/60]1/2*60/i
Ahighprobability(95%)oftruedetectionistheobjective,andthesurveyiswillingtoaccepta highprobabilityoffalsepositivedetections(60%)withresultinginvestigations.Thevalueofdis selectedfromTable6.1inNUREG1507tobe1.38.
A3
Toaccountforlessthanidealsurveyperformance,asurveyorefficiencyfactor(p)of(0.5)1/2was alsoincorporatedintothefinalcalculationofbetascansensitivityasfollows:
(B2)
(0.5)1/2*(cpm/dpm)(probearea/100)
Theresultingvaluesareapproximately1500dpm/100cm2forthe4368detectorandanaverage of390dpm/100cm2forthe4337detector.Ifonlyasingle100cm2areaispresent,thescan sensitivityforthe4337detectorwouldbeapproximately2280dpm.
BetaActivityStaticMeasurements
Static measurements of beta surface activity are performed using 4368 detectors. A static measurementisperformedbyplacingthedetectoronthesurfaceandallowingittointegratethe countforaperiodof2minutes.Theminimumdetectablebetacontaminationlevel(MDC)is calculatedasfollows:
MDC=[3+4.65(BKGD)1/2]/(efficiencyfactors)(detectorarea/100)(counttime)
Theresultingvalueisapproximately470dpm/100cm2.
RemovableAlphaandBetaActivityMeasurements
Smearsforremovableactivityarecountedfor2minutesinaLudlumModel2929alpha/beta counter.Thebackgroundsare1alphacpmand25betacpm;4detectionefficienciesare0.25 alphaand0.20beta.Usingthesameequation(withoutprobeareacorrection)asabovefordirect measurementsyieldsremovableactivityMDCsofapproximately19alphadpm/100cm2and90 betadpm/100cm2.
References
- 1.
MultiAgencyRadiationSurveyandSiteInvestigationManual(MARSSIM),NUREG 1575(Rev.1),USNuclearRegulatoryCommission,2000.
- 2.
MinimumDetectableConcentrationswithTypicalRadiationSurveyInstrumentsfor VariousContaminantsandFieldConditions,NUREG/CR1507,USNuclearRegulatory Commission,1997.
B1
APPENDIXB
SampleOutlineofReleaseSurveyReport
1.0 ExecutiveSummary 2.0 Introduction 3.0 PurposeandScope 4.0 SiteDescription 5.0 RadionuclideContaminantsandCriteria 6.0 SurveyApproach 7.0 SurveyResultsSummary 8.0 Conclusion 9.0 References
Attachments
Fielddata(electronic)