ML17037B931

Nine Mile Point Unit 2 - Letter Regarding an Enclosed Progress Review of Program for Evaluation of Geologic Structural Discontinuities as of April 30, 1977 - Cooling Tower Unit

ML17037B931
Person / Time
Site:	Nine Mile Point
Issue date:	05/06/1977
From:	Rhode G K Niagara Mohawk Power Corp
To:	Case E G Office of Nuclear Reactor Regulation
References
Download: ML17037B931 (14)

Text

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FNCLOSURE APPENDIXSUMMARIZING TPEWORKANDTHE'INTHRPRE-TATIONSOF.APPLICANTS INVESTICATXVE PROGRAM..

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II.Y.I3202~,lMay6,1977gavx>>~77il04%KRMM7MMEll:ilL3lINP7;Mr.EdsonG.Case,ActingDirectorOfficeofNuclearReactorRegulation U.S.NuclearRegulatory Commission Washington, D.C.20555Re:NineMilePointUnit2DocketNo.50-410

DearMr.Case:

Wehavepreviously informedmembersofyourstaffandtheOfficeofInspection andEnforcement ofcertaingeologicfeaturesatourNineMilePointUnit2construction site.OnApril11and12,1977,wediscussed additional discontinuities observedinthecoolingwaterintake-discharge shaftandon'April29andMay2,1977wediscussed adiscontinuity observedinthewalls'fadrainageditchconstructed adjacenttoandparalleltooureastpropertyline.Observations ofthesediscontinuities andcomparison withotheron-sitefeaturesleadtotheconclusion thatthesenewlydiscovered featuresarealsoinactiveandofnoseismo-tectonic significance.

Thesenewobservations areentirelyconsistent withtheearlierinterpretation ofotheron-sitefeatures.

Evaluation ofthesenewobservations willbeconsidered inthecontextoftheinvestigative programdescribed inmyletterofJanuary24,1977.Theprogramisexpectedtocontinueforseveralmoremonthsandtoaddressthecombination ofgeologicfeaturesnotedatthesitetodate,including thediscontinuity foundinthewallsofthedrainageditch.

.~4'0lI~ult4Wrl\41 Mr.EdsonG.Case.U.S.NuclearRegulatory Commission PageTwoMay6,1977DuringourmeetingwithmembersofyourstaffonApril14,1977,DamesandMooreprovidedadditional information tosupportearlierinterpretations ofthecoolingtowerfeatures.

WehaveattachedheretoanAppendixwhichsummarizes todatetheworkandtheinterpretations ofourinvestigative program.Asindi-catedintheAppendix, DamesandMoorecontinues tointerpret theevidenceassupporting thepositionthatthecoolingtowerfaulthasnoseismo-tectonic significance anddoesnotrepresent ahazardtotheoperating unitsatthesite.Verytrulyyours,NIAGARAMOHAWKPOWERCORPORATION GeaidK.odeVicePresident

-ngineering

/sjzAttachment Xc:Mr.T.K.DeBoer,DirectorTechnical Development ProgramsNewYorkStateEnergyOffice

APPENDXXProgressReviewofProgramforEvaluation ofGeologicStruc-turalDiscontinuities atNineMilePointasofApril30,1977-CoolingTowerFaultExcavation

-ofTrenches-Todateaseriesoffivetrenchesandanexploratroy pathavebeenexcavated acrossthetraceofthefaultexposingtheoffsetsinthebedrockforadistanceofapproximately 2500feet(Figure1).TrenchesNo.1and2tothenorthwest ofthecoolingtowerareawereexcavated tobedrockandthefaultzonewasnotpresentateitheroftheselocations.

PitNo.1wasexcavated overthefaulttobedrock.TrenchesNo.3and4havebeenexcavated tobedrockandaslotapprox-imately3'x10'x8'eep hasbeencutintothebedrockacrossthefaultzoneateachlocation.

TrenchNo.5hasbeenexcavated tobedrockandasimilarrockslotispresently beingcut.Thelastsignificant episodeoffaultingappearstohaveoccurredduringtheCretaceous Periodwithnotectonicmovements withinthelast70to100millionyears.Themostrecentsurficial movements involving sediments havebeenplaced"within thelast13,000years.Webelieve,atthe'presenttime,thatsufficient evidencecanbeobtainedattheexistingexploratory sitesforanevaluation ofthepossiblemechanisms of'surficial deformation andtheprobability ofreactivating thiszone.2.'rill'ing

-Adrillingprogramtoexplorethenatureandorrentation ofthefaultinghasbeeninprogresssincelateFebruary.

TodatetenNXboreholes havebeendrilledtoanaveragedepthofapproximately 200feet.Theseholesarepositioned attwoseparatelocations andarepatterned toprofiletherockstrataacrossthefaultzone.Rockcoresanddownholegammaraylogsarebeingcombinedtoproducestratigraphic logsforeachboringtoaidinthedetailedcorrelation ofbed-rockunitsacrossthefault.3.M~apin-Geologicmappingandstructural analysisofthebedrockandoverlying materials hasbeencompleted forthewallsandfloorsofTrenchesNo.3,4,and5.ThemappinginPitNo.1istocommenceshortly.SlotscutintothebedrocktoexposethefaultincrosssectionhavebeenmappedinTrenchesNo.3and4;SimilarmappinginTrenchNo.5willbeperformed whenthatrockslotiscompleted.

eeee 4~SamplinandAnalysis-Rockcoreshavebeenextracted fromboththe.sandstone andshaleunitsandlaboratory testedforadetermination ofthestrengthcharacteris-ticsoftheserocks.5.TrenchesNo.3and4andapollenanalysishasbeeninitiated forcorrelation purposesandtoascertain therelativeagesofdeposition ofthesediments over-lyingthe'edrock fault.Samplesfromtheoverlying peatboghavebeentakenandarebeingdatedbyradio-carbonmethods.Rockcoreshavebeencollected andanalyzedformineral-ogicalcontent.Geochemical analyseshavebeenperformed onmineralcrystalssampledfromthefaultzone.Thesedataaidinevaluating thedepthofburial,temperature offormation andageofthematerials.

6.Geomorphology

'andStrati'aohy ofGl'acialandPostGlacial'epos'z'ts

-Regionalgeology.c andgeomorphic literature searcheshavebeenconducted.

Thesestudiesinvestigated thepossibility ofsimilargeologicstructures intheareaandtherelationship'of thestructures atthesitetothegeologichistory.Emphasishasbeenplacedonthegeologichistoryoftheareaforthelast15,000years.lakeandlandlevelsforthisperiodhavebeenplottedandstudiedtoevaluatethereboundcharacteris-ticsresulting fromunloading theglacialiceandwaterthatcoveredthearea.Thepossiblerelevance ofpop-upsduringthistimeofunloading isalsounderinvestigation.

7~Stre'ss'ea'surement

-Stressconditions intheregionhavebeenevaluated andaprogramisunderwaytomeasureinsitustressconditions atthesite.Themeasurement ofstressesinthebedrockutilizestheovercoreandtheovercore/undercore techniques.

Oneovercoreboreholehasbeencompleted toadepthof95feetanddrillingatasecondlocationisinprogress.

8.Sei'smi'ci'ty

-Areviewofseismiceventsintheregion1tectoniceventsintheareaanditsrelationship tothesite.'INTERPRETATION ANDCONCLUSIONS

-Dames&Moorebeganitspre-lrmrnaryrnvestrgatron oftttocoolingtowerfaultsoonafteritsSeptember 29,1976discovery.

OnDecember13,1976adetailedgeologicinvestigation wasinitiated.

Thisinves-tigationisongoingandisscheduled tocontinueforseveralmoremonths.Agreatmanyoftheplannedtaskshavebeen

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Amajorpartoftheincompleted work,asofthisdate,isrelatedtotheboringprogram.NXcoreboringsacrossthefaultzonesareapproximately 80percentcomplete.

Theovercorestressmeasurements are15percentcompleteandthesurfaceovercore/undercore programisjustgettingunder-way.Thecompletion ofthesetaskswillprovideanunder-standingoftheinsitustressfieldanditsrelationship topastandanypossiblefuturerecurrence ofmovementatthefaultzone.Ananalysisandevaluation oftheevidencetodatecontinues tosupportmajorportionsofourearlierinterpretation.

Thereappeartobethreedistinctmovements associated withthefaultzone.Thefirstmovementwastheformation ofthestrikeslipfaultduringthePaleozoic Era,morethan200millionyearsago.Thisfaultexperienced about,3feetofleftlateralstrike-slip movement.

Asecondmovementproducedthemonoclinal flexuring.

Analysisofmineralsthatcoatdipslipslickensides suggestthismovement.

mayhaveoccurredduringtheCretaceous Period,70to100millionyearsago.Thethirdandlastmove-mentwaspreviously judgedasapop-upalongapre-existing fault.Itischaracterized bysmoothfoldinginthebedrockclosetothefaultzone,foldedbrecciated zones,beddingplaneslip,andsmallhigh-angle reversefaultsintheglacialandpost-glacial deposits.

Althoughthesefeatureswereprobablyproducedbythesameconditions thatarethoughttoproducepop-ups(glacialiceandlakeunloading andhorizontal stresses),

therateofreleaseisconsidered tobedistinctly different fromthatcommonlyassociated withpop-ups.Weinterpret thisQifference tobeaslowenergyreleasethatcouldnotproduceaperceptable seismiceventinsteadofthealmostinstantaneous stressreleasegenerally associated withtheformation ofpop-ups.DamesaMoorecontinues tointerpret theevidenceassupporting thepositionthatthefaulthasnoseismo-tectonic significance tothesiteandwefeel,atthistime,thatthereisnoreasontosuggestthatthefaultrepresents ahazardtotheoperating unitsatthesite.

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