Eugene S. Grecheck , DominioffVice President W W

Nuclear Development

Dominion Energy, Inc. • Dominion GenerationInnsbrook Technical Center5000 Dominion Boulevard, Glen Allen, VA 23060 August 11, 2010Phone: 804-273-2442, Fax: 804-273-3903E-mail: Eugene.Grecheck@dom.com

U. S. Nuclear Regulatory Commission Serial No. NA3-10-012Attention: Document Control Desk Docket No. 52-017Washington, D. C. 20555 COL/BCB

DOMINION VIRGINIA POWERNORTH ANNA UNIT 3 COMBINED LICENSE APPLICATIONPROBABILITY OF MISSILE GENERATION FROM LOW PRESSURE TURBINES(FSAR CHAPTER 10)

This letter submits Mitsubishi Heavy Industries, Ltd. (MHI) technical report MUAP-1 0005-PRev. 0, Probability of Missile Generation from Low Pressure Turbines (proprietary version),and MUAP-10005-NP Rev. 0 (non-proprietary version), for NRC review.

As discussed in COLA Part 7, Departure 10.2(1), the North Anna Unit 3 design of the lowpressure turbines (LPTs) and selected balance of plant power production equipmentperformance requirements are modified from the US-APWR standard plant design toaccommodate the use of a different set of LPTs. The enclosed MHI technical report, whichis referenced in FSAR 10.2.6, assesses the integrity and safety of the North Anna Unit 3LPT rotor design in order to establish requirements on the nature and frequency of in-service rotor inspections.

Enclosure 1 contains technical report MUAP-10005-P Rev. 0, which is marked"Proprietary." This report should be withheld from public disclosure in accordance with 10CFR 2.390(a)(4). An affidavit from MHI providing the justification for treating the report asproprietary is provided as Enclosure 2. Enclosure 3 contains technical reportMUAP-10005-NP, which is marked "Non-Proprietary."

If you have any questions or require additional information, please contact Gina Borsh at804-273-2247.

Very truly yours,

Eugene S. Grecheck

Serial No. NA3-10-012Probability of Missile Generation from LPTs

Page 2 of 2

Enclosures:1. MUAP-10005-P Rev. 0, Probability of Missile Generation

Turbines, June 2010 - Proprietary Version2. Application for Withholding and Affidavit3. MUAP-10005-NP Rev. 0, Probability of Missile Generation

Turbines, June 2010 - Non-Proprietary Version

from Low Pressure

from Low Pressure

Commitments made by this letter: None

cc: (distribution w/o enclosures except where noted with an *)U. S. Nuclear Regulatory Commission, Region II *C. P. Patel, NRC *J. B. Jessie, NRCT. S. Dozier, NRC *J. T. Reece, NRC

COMMONWEALTH OF VIRGINIA

COUNTY OF HENRICO

The foregoing document was acknowledged before me, in and for the County andCommonwealth aforesaid, today by Eugene S. Grecheck, who is Vice President - NuclearDevelopment of Virginia Electric and Power Company (Dominion Virginia Power). He hasaffirmed before me that he is duly authorized to execute and file the attached documentson behalf of the Company, and that the statements in the documents are true to the best ofhis knowledge and belief.

AkolVd fa--Acknowledged before me this day of ,2010

My registration number is "7/ 73o -

NA3-10-012Docket No. 52-017

Enclosure 1

Proprietary Version

MUAP-10005-P Rev. 0Probability of Missile Generation from Low Pressure Turbines

June 2010

NA3-10-012Docket No. 52-017

Enclosure 2

Application for Withholding and Affidavit

MITSUBISHI HEAVY INDUSTRIES, LTD.

AFFIDAVIT

I, Yoshiki Ogata, state as follows:

1. I am General Manager, APWR Promoting Department, of Mitsubishi Heavy Industries, LTD("MHI"), and have been delegated the function of reviewing MHI's US-APWR documentationto determine whether it contains information that should be withheld from public disclosurepursuant to 10 C.F.R. § 2.390 (a)(4) as trade secrets and commercial or financial informationwhich is privileged or confidential.

2. In accordance with my responsibilities, I have reviewed the enclosed document entitled"Probability of Missile Generation from Low Pressure Turbines MUAP-10005" dated June2010, and have determined that portions of the document contain proprietary information thatshould be withheld from public disclosure. Those pages containing proprietary information areidentified with the label "Proprietary" on the top of the page and the proprietary informationhas been bracketed with an open and closed bracket as shown here "[ ]". The first page ofthe document indicates that all information identified as "Proprietary" should be withheld frompublic disclosure pursuant to 10 C.F.R. § 2.390 (a)(4).

3. The information identified as proprietary in the enclosed document has in the past been, andwill continue to be, held in confidence by MHI and its disclosure outside the company islimited to regulatory bodies, customers and potential customers, and their agents, suppliers,and licensees, and others with a legitimate need for the information, and is always subject tosuitable measures to protect it from unauthorized use or disclosure.

4. The basis for holding the referenced information confidential is that it describes the uniquemethodology developed by MHI for assessing the integrity and safety US-APWR integratedturbine rotor. That methodology was developed at significant cost to MHI, since it requiredthe performance of detailed design calculations, analyses, and testing extending over severalyears. The referenced information is not available in public sources and could not begathered readily from other publicly available information. MHI knows of no way theinformation could be lawfully acquired by organizations or individuals outside of MHI.

5. The referenced information is being furnished to the Nuclear Regulatory Commission ("NRC")in confidence and solely for the purpose of supporting the NRC staff's review of Dominion'sApplication for a Combined License for the North Anna Power Station (Unit3).

6. Public disclosure of the referenced information would assist competitors of MHI in theirdesign of new nuclear power plants without the costs or risks associated with the design ofnew systems and components. Disclosure of the information identified as proprietary wouldtherefore have negative impacts on the competitive position of MHI in the U.S. nuclear plantmarket.

I declare under penalty of perjury that the foregoing affidavit and the matters stated therein aretrue and correct to the best of my knowledge, information and belief.

Executed on this 6 th day of July, 2010.

Yoshiki Ogata,General Manager- APWR Promoting DepartmentMitsubishi Heavy Industries, LTD.

NA3-10-012Docket No. 52-017

Enclosure 3

* ( Non-Proprietary Version

MUAP-10005-NP Rev. 0Probability of Missile Generation from Low Pressure Turbines

June 2010

Probability of Missile Generation from Low Pressure Turbine ftA1i AP_10 nN Jr;--KP IlP'lI /

ProbabUlity of Missile Generationfrom Low Pressure Tuerbines

INon Proprietary .Vrsionl

June 2010

©02010 Mitsubishi Heavy Industries, Ltd.All Rights Resered

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Probbbilitv of MissileGeneration from Low Pressure Turbine MUAP.10005-NP t'R0)Piobabilitv of Missile Generatioh from Low Pressure Turbine MUAP-1 0005-NP (R0~

Designed :

Ch'ehked:

Shingo Hira ý-Sbnior. EngineerT.urbinie Plaht. Engi6eerinhp SectionNuciea4r Turbihe ,Planit Engineerring Dep rtment

Kohji Tanaka Senior En:gin !er"Turbine Plant Engineering.SectionNuclearTurbine PintiE:n eering.Department

Hideo Tateishi M6a6a@Igeq .r ""Turbie Pliant Enginebieihg4 SectionNuclear Turbine Plant'EnginpeIring Department:

Date

9aW

Date

Aproed

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Probability of Missile.Gen'eration from Low Pressure-Turbiqne'

Revision History

Revision Pa e De0 1 All I Oidiinal lssue.

• MUAP-1,0005-,NP (R0)

I sizription

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Probability of Missileý'Generaition from Low Pressure Turbine MUAP•10005-•NPI (R)Probability of MissileGeneration from Low Pressure Turbine MUAP~1 0005-NP (RO)J

Abstract

The purpose6of this document and ana!yses is.to show the probability of missile generationfrom inte'gral low pressure rotors.

Four fail uren mechanisms are evaluated; deStructiv6' oveierspeed burstihg, fracture due to bi•h•cycle fatigue, low cycle fatigue and stress corrosion. Stress corrosion cracking was identifiedto be the dominant, mechanism to determine the probabilitY Of missile generation.

The probability of missile.;generation by thtis mechanism does not exceed 1i0. per year evenafter ( ] of running tiinme; It is concluded that' the NRC safety guidelines can be satisfied

:troughethbperiodictinspetionin a p'Oiper interval withini

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P.robabiiitv of Missile Generalion fromn Low :Pressure Turbine, ,MUAP-.10005-NP (R0)PoailtofMsieG ertofrrLoPrsueTrieMA- 005N (RO

Table of Contents

List of TablesList of FiguresList of Acronyms

1•0, INTRODUCTION

2.0 DESIGN FEATURES2.1 Material Feature:

3.0 PROBABILITYWOFMISSILE GENERATION3.1 Ductile Bdrst.3.2 Fracturieq u D6ueT7o" HighCycle Fatigue (HCF)133 Fracture Due To.Low ycle Fatigue (LCF) -

, Startup/ShutdownCycles

3.4 'Fracture• Due TStriess'.rr'doiorsn Cracking (SC C).

4.4: DISCUSSIONAND CONCLUSIONS

5.0 REFERENCES

IV,

1-1

;2-1

3-.1

'3.:2-13.3-1

3.4•-1

4-l1

'5-1

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P'robabilitY of Missile Generation from Low Pressure Turbine, M UAP-;I0005,-NP (R0)

List of Tables

Table 3.1-, ,safety .Factors for Ductile BurstingTable 3.2-1 HCF-PeakAlternating Stresses and Safety Factors due to

Gravity Bending and Possible Misalignment of the BearingsTable 3'3;I 3.5% Ni-Cr-Mo-V RotorSteel, An and C0Q Parameters in the

Paris EquationTable 3:3-2. Probability of Low Pressjfe Rotor Brittle RuptL'.e due to

Low Cycle Fatigue (start-up/shut-dbwn 9ycle)TabIe,4;4'.4- 3"5% Ni-Cr-Mo-, Rotor Steeil Crack Growth Rate Deviation

from CalculationTabl, 3.4-2 -Probability ofMissile.Generati'on (per year) due to Stress

Corrosion racaking

3.-2T3

3.3-3

3.3-3

3.3-334-3

3.4-5

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Pfobability 6f Missile Generation from •Low Pressure Turbine ,MUAP-1 0005'-NPý (FRO)Probability of Missile Generation fromLow Pressure Turbine MUAP-10005-NP (RO)

LiSt ofL Fiures

Figure'.2-1Figure 21-1Figure 3.3-1

Figure 3.4- 1

Ty pical Integral Rotor StructureTypical Integral Rotor Material Test LocationsTemperature Distributions in the LP Rotor (at RatedCondition)Probability of Missile Generation (per year) due to StressCorrosion Cracking

2-12.1-13,3-4

3.4-5

WMitsubishi Heavy Industries, LTD. iii

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Probabilitv'ofMissileýGeneiration from Low Pressure Turbineý MUAP-100054NP (RO),

List OfAcrdOnyms

The foilowing list defines the acronyms used in this document.

a Crack, Size in Depthai Initial Critical -Crack 'Size. in. Depthacr .Critical Crack Size in DepthF Flaw, Shape Parameter = SQRT (Q1.2 1,),FATT Fracture Appearance Transition TemperatureHCF High Cycle.FatigueKic Fractuire.Toughness (of the rotor)LCF Low. Cycle FatigueLP rotQr Low"Pressure Turbine RotorN Number of Cycles (ex. NumberQf .Start &: Shut-d6wn).Ni ý4 U Number:of Cycles of FailureOS: .Over SpeedPscc Psro'bability of Missile Generat"ion due'to SCC'qI Prbbbabiiity of Crack InitiatiOn.Oar Probability of Flaw Propagation to-.Cr.itidtcal Crack Size.qos Probability of Reaching Design OerspeedQ Flaw Shape ParameterSCC Stress C0rrosion CrackingSF Safety. Factor (ex. A jaia• /An" peak ),T TemperatureTS Tensile StrengthYS 'Yield Strengthy Crack. Depth Growth RateE ýLUncertainty Terma Stress

U fail Failure Stressays YieldStr'engthA u Stress Range.A o al, Allbwable' Stress Range'A :Failure Stress RangeA"peak .Pek (Maximum) Stress Range4 C pek, - ': ., - e ... ,. . .AK Stress Intensity, RangeAKIh, Threshold Stress Intensity Range.

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Probabilitv.;of Missile Generation fr'om •LoWv Pressure Turbine- ..MUAP-10005-NP.('R0)

1,.0 INTRODUCTION.

A typical steam turbine for modern nuclear power stations consists of a double flow highpressure element and two or three double flow low pressure elements in tandem. The rotor ofthe high pressure element generally consists of a single forging with blades being attached ina fashion dependent upon 'the specific manufacturer's preferences. On the other handrecently, a larger size of nuclear low pressure rotors has been used to structure together theindividual shaft and discs. Each disc is usually shrunk on and keyed to the shaft.

Advancement in steel making technologies and facilities mitigated the restriction for the size, ofhigh quality ingot and the size of forging in the manufacturing process of low pressure rotors.This advancement made possible the application of the: high quality integral low pressure rotorto the nuclear turbine. The advantage of applying integral low pressure rotorsi, which are-tobe applied to US-APWR, is discussed in the following sections.

The purpose of this document is tob assess the integrity and safely of US-APWR integral LProtor designs in order to establish requirements on the nature. and frequency ofin-iservice rotorinspections. This assessment is accomplished by evaluating the possibility of a rotor fracturewhich could lead to bursting and missile generation from the low pressure turbine.

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Probability of MissileGeneration from Low Pressure Turbine MUIAP-i0005-NP (R0

2.0 DESIGN FEATURES.

A typicali'ntegral rotor is shown in Figure 2•1. A major advantage of this design is theelimination of the disc bores and keyways. Rotors with, shrunk-on discs have peakl stresses:around the locations where' the discs are shrunk-on and keyed to.the shaft. The eliminationofthese structures ha's shifted. .the lo'ation of peak stress from thie keyWas to blade fasteningregions at the rim (of the rotor, whose lo'cal stress is much lower than that of the shrunk-ondiscs. Since cracks ,iarelikely to occur in high stfessedjregions, reduction of the peak stressthroughout the ýrotor significantly contributes to the reduction.of the rotor burst probability.,

In addition- to lower' local stress throughout theý rotor,,t•e integral structure also has the benefitof 'reduced "averaige etangential stress of-the discs and this fact allows ,us to apply6 loweryieldstrength mate, ria ,With traditional safety margins rebaining as they are.. The inte ral ritorforgin-g-s ar heat-titreatOd to- obtain minimum yiel#dstrengths of [ ] depending: u-pon the;requirements o•the particular application. Many.,yearsof experience and testing of.the -36:5%Nir-d'r-Mo-V alloy steel rotor material have .demonstrated better ductility, toughness andresistance to'^str~ess corrosion cracking at a lower yield, strength,. These, benefits can beimportIantfactor-sto reduce-the possibility of'tur'bire missile generation.

C

Figure 2-1 Typica inHtegral Rotor Structure

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Probability of, Missile. Generation from Low. Pressure.Turbine MUIAP,-10005-NP (R0)roaiiyo isl eeainfo o rsueubn MA105-NP (R

2.1 Material Feature

In addition to increased :capability of manufacturing large size Of rotor forgings, improvementsin the steelmaking process has. resulted in improved toughness, uniformity of properties andreductions in undesirable embrittling elements than were. previously achieved.

The ispecification for integral rotors-requires testing at the"locations shown in Figure 2.1,1 toconfirm uniformity of the rotor. Usihg these specimens, the tensile test (tensile strength; yieldstr I ength; elongation and area"reduction), and impact test (absorbed energy, 50% FATT an.dupper..shelf en•rgy) shall 'be performed ,and confirm if thekiequired:speqifications .are satisfied.

TargetýSPectmen/ ,.YUJ7IlgFfr7] Ti

Figuree 2.1-1 ýTypical Integral Rotor Mateeial Test Locations

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Probability of Missile Generation frorm Low Pressure Turbine MUAP-10005-NP (IRM

3.0 PROBABILITY OF MISSILE GENERATION

Four potential failure mechanisms are considered for the assessment of the missile generationprobability of an integral low pressure rotor;

1, Ductile burst,

2. Fracture due to high cycle fatigue(HCF),

3. Fracture due to low cycle fatigue(LCF),

4, Fracture; due to stress corrosion &a~cking(SCC).

For the purposes of conservative analyses, a rotor burst is considered sufficient to create amissile: although it 'is recognized that the turbine casing could provide resistance againstmissiles breaking out to the external, The methodology and results~for each of the failuremechanisms are analyzed and discussed in the following sectiOns.

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Probability of Mis~sile.iGenhbratibn from Low, Pressure Turbine M ULAP- 10005.NIP.4 1RO)

3.1 Ductile Burst

Tests have been performed'by a number of investigators in which-mbdel' turbine discs havebeen spun to the point of failure. The results demronstrate that ductile failure' can bepredicted by assuming.the a-veragetangential Stress equalto the tensile strength of the dis:c at

burst. It becomes possible to calculate the speed at which failure" would occur by .knowihgthe stress -required, for failure., The integral' rotor body is divided into individual discs asshown in, Table 3.1-1 .for this analysis. To be more conservative, it is :assumed that failure.occurs when the average tangential stress in any individual disc is.equal to the [ ]of the disc .rather than the tensile strength.

The.,r.esults bf, this !analysis are' summarized: in'Table 3.1-1.. We ccan conclude from thiSt.analysisthat ductile bursting of the r6tor willnot occurf untiltheo:speed of the rotor is increasedtol equal or be, grieater than [ 66, alth#gh tisth analysis is conserativelyevaluated ýby using[f . . Since this is-well beyqnd:the-design overspeed, the rotorcannotfail by, thismirechanism unlessAthe I`

]. Thelprobabiity of thiS event is therefore deterrhinerid.by thei],,,,and periodic rotor insPections have ho effect on the probability Of

failure.by thi.s riechKnism,

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Probability of Missile Generation from Low Pressure Turbine MUAP_-10005-NP (R0)

Table3.1-1 -Safety Factors for.Ductile Bursting

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Probability of Missile Generation from Low Pressure Turbine N MUAP-IOOO5-N WRO),.

3.2 Fracture :DueTo High Cycle Fatigue (HOF)

'In this scenario itis, postulatedlthat a failure can occur'from a fatigue crack which propagates:in a plane transverse to the rotor axis as a result of!cyclic"bending loads on the rotor. These-loads are developed by gravity bfOrces.-a'nd by possible misalignment of the bearings. Missilegeneration b~y th'ismechan~ismis highly'unlikeIy since:1. Large safety factors used in thedesign rnnimize-thelinitiation and propagation of a fatigue

crack.2. 2Ak large 6ransverse' crack will create eccentricity and the resulting higt vibrations willicause,

ft-he iit.'tb be removed~ fromn service beftorefactr ocurs.

In ordeIr to as sure that the rotor burst ,by this scenaio' ,will not occur during service.operation.,the folloWingn Welss are to be done;

1. Initiation o6f HCF cracks,

2. .Propagation of:;cracksby HCF.

initiating. a HC Fcradc-ksar6eevaluated by comparig,'the magnitude of the bending ,stress with:the failure bstress§aa obtained from a Goodman Diagram' and reduced to account for size",effects. Table_:.2 3_.2-1shows the. calculated safety 'factor, against 'HCF at. each surface positionof each 1ow pressuredrotor.-I t is seen that [ - is the location whereitIhe.minimum safety factor :f [. ] is observed, while the -safety factor on the same position is'.bigenoughtob preveht,,the, initiation of cracks due to H&IF These'rotors therefore have s fficient-strength ag.inst-thee HCF 'fracture from theviewpjint••of•a'k initiation.

The propagatio, n of apostulated.'pre-existing crack"isevai.uated as follows:

The rotors have he thereshold stress'ntensity range Lth', for fatigue crack, propagation .and

that is •obtained frorq , thisrIelation:,

(3.1)- AK th=F.A ,*a

Where .&0."i the all: t dianannating bending stress and, ia i: the• xisting crack size in depth, Andthe flaw shape parameter: F' is obtained as, below:'

(3.2)- ,F=:• 1:1

where. Q,.the.:flaw shape, parameter is' also determine4d by assuming a semi-elliptical crack atthe materialsurface: Thernumber of Q is'[ ]'when assuming the depth to length:-ratio off[ 1].

For the purpose of 6o-servative analysis and obtaining allowable vibration stress AOca,, thethreshold stress intensity range AKth is assumed to be.,[

].I nitial crack size, a, 'is assumed tobe[

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Probability,"of Missile.Generation from Low Pressure TurbineMR NUAP-1 0005-NP,(,R0)

(3.3), A o;,AKA Q.7n

By com paring the peak stress withthe allowable vibratorystress, in Table 3.2-1, all of the peakstresses A crp,,, are well below the minimum allowable vibratory stress AJ 'I; It is. thereforeobvious that the rotors have a sufficient safety margin in regard to the, propagation of apostulated pre-existing crack.

It is concluded that low pressure rotors have sufficient safety factors adgainst HCF. Andperiodic in-service inpcin ortases fatigue fractures are not~ required.

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ProbabilitVo• oMissile Generation.from Low Pressure Turbine ..MUAP-1,0005-NP (RD).

Table 3.2-1 HCF Peak alternating Stresses' and Safety Factors due to GravityBending and Possible Misalignment of the Bearings

F E D C

B

A ...

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Prob~ability of Missile. Geneiration from~il•0w Pressure Turbine ,MUAPF 10005-N P.(R0)

3.3T Fracture Due To Low Cycle Fatigue (LCF)- Startup/Shutdown Cycles

An analysis was carried out to.deiermine the probability of turbine. missile generation due to;.startup-shutdown cycle fatigue crack growth. In this postulated scenario, the failuremechanism'is a brittle fracture, where. a crack.initiates at the center ofthe rotor, and grows to acritical size as a result.of speed cycdling, during the operating life of the turbine.

Such prob'ability of failure depends on the magnitudes and interrelatidnships of the following,,six factors:

1. The size of cracks at the center• of ,the rotor at the beginning of Iturbine operation

2. The shape pfjthese cracksf3. Thesize of the critical track (depenhdent on, the exposed :stresses-at running speed ordesig h.Verspeed and toughnessruofnthe rostor)

4.4 The magnitude of'the stre ssrang ecyclesexperienced dui'ng th•e peration of machines

o&6. The!two parameters, co and ninthe Paris fatigue crack growth ateý,eqat ion:

da(3.4) - ýC0 (AK)n

wherie da/dN is the crack&grOWth rate. per cycle, AK is .the ýst•ess intensitV range, and nad C-0 are, parametersý to'. determine the fatigue crack growth rate which ':are 'determined-experimentally.

:These-factors are'related:to,:thernumbýer ofcyciesof.failure Nf by :theequation"

i 3 . ) ' N , . . . 2 _ '( a ' -2 ,) / 2 .' • =( n -2 ) / 2 •( ) N, = . '" 2 \a 0 n jc "

where

N, = The number of.,cyc esi;to reach criticai crack size

.M =7r/Q

SQ =Flaw shape parameter

a1l Initial largest crackideptht

.at .= Critical crack deptft.

Ad =Range of stress (yclesin operation:

In the .estimation of the pTrobability of rupture by this sceniario, both 'C6. 'and n factors

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Pqrobabilitv of'Missile Ge'neratibn,ý,r,6m-Lo*w'Fressure Turbine MUIAP-10005-NP ('R0)

described above are considered to, be random variables, and other parameters are.conservatively determined. The hu-mber of cycles to failure Ni. is then dependent on theprofile of the above variables. The profilesof the random variables and other parameters aretaken as follows:

The flaw shape parametere Q is:.determined by .:assuming that a semi elliptical crack with a.qdepth:t6'lenrgth ratio of[, I isý formed at the center"of the rotor. Sucb a flaw cracks.hapeparameter would be[ ], which is independent on the stress. Q can,tbe set to be[ I as a:conservative number..'Thecriti'cal crack size ab,, is obtainedtf•i. the relation:

(3;6), ar

'where K•c is

Probability of Missile Generation from Low Pressure, Turbine MUAP-1 0005-NP (R0)

Table 3;3-1 3.5%' NiCr-Mo-V Rotor Steel, n and Co Parameters in'the Paris Equation:

da =

Table 3.3-2 Pirbability of Low PressUre Rotor Brittle Rupture due tb LoW Cycle'Fatigue (start-uplshut-dOwn, 6cyl)

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Probabilit of Missile Generation fiem tLowPressre Turbine MUAP-10005-NP (R0)Probability of Missile Generation from Low Pressure Turbine MUAP-10005-NP (RO)

Figur 3.0!3-l' Temper#ature Distributions' in the LP Rotor (At,.Rated :Cond0tiorn)

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Probability ofMissile- IGeneration fromLow Pressure Turbine M UAP-,10005,-NP :(IR )I,Prbb-t of ,isl eeaio rmLwPesr Tubie.UA .005N (R

3.4 Failure Due-To Stress Corrosion Cracking (SCC)An anralysis -Was perf•ormedlto deteemine the probability ofintegral rotor bursting dueto SCC.

A cralck is. assumed to.jinitJate at the rim where the stresses are.the highest, and propagateinward'inradial direction until it reaches the critical cracksizpe before bursting, The probabiity

of rotor'fracture due to this failure mechanism is..a"function of the- probability of crack initiation,the rateat"which acrack' cdula, grow due to stress corrbsionj, and, the critical crack, depth that,will lead to a burstý at-:either the runnihg speed, orthe design overspeed. Each of thesefactorspis di¢scussed below.For this~analysi's; it is only necessary to'consider[:

on the rotor.' [ ].of the LP rQtor'is exposed to .superheated steam andexperience has, demonstrated that SCC does not:occur in dir:superheated steam.

The probability dof missile generation due to SCC is,'expressed' as follows:

(8.7~) pscc; qiq~r*-qo5

where',q isitheo probabilhityof crack initiation, q&. is he probability ofz flaw propagati on ,up to t.he.critical sizte bySC,SQ and q0o is' the probabilitythat the unit will reach design overspeel. Forthe' purpos of conservativ-e evaluation, it is asumed that q1 is. regarded as 100%,. ,even

througbh MHI has. hot found cracking during ihspections on integral rotors. . is alsoasslued to0 beýb- 1A00%, nevertheless it is presumed to- e in the .Order of 10 undebr properinspection and maintenance for turbine:valves-and the* control system.

Thanks to',the full integral'rotor design withouVt-zshrunk-on and keywaysland-to a relatirely lowyield strehgth of about [ ], we have no experience of emanating SCC oh Jfullintegral 'VIrpressure: rotors. However, probability:"analysis for r'otor failure due to SCC iscarriedo9ut. base.don ex",ýppe rimental, and field"data of high!yield. stress.'materials for'conservativepurposes;

3.4. ,Crack, GrowIth Rates.

The crack -growth rate model! used 'in .this analysis 'isexpressed as follows:

(3.81) ]S ..i I Iwhere'.[

The actual numbers,,usedfor this analysis 'are the srame as those obtained in the experiencefor keyway stress-corrosion crack growth rate in built-up rotors:

[ ,L

[I

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P robability of Missile Generation'from Low Pressure Turbine, MUAP-,40005-NP.IR0Pobiit ofMsieGnrtofrmLwPesr ubieMA-00-P(O #

Normal distribution of ze with a mean -value of I was used.The distribution of E. was obtained from crack growth rate data for the 3:5% Ni-Cr-Mo-V rotorsteel presented in Table 3.4-;1. Although these'rotors have different. mechanical propertiesfrom that of the integral rotor, the crack growth rate uncertainty e can be regarded-to be thesame because of.the same, chem-ical compositions.

The calculations were caarried out;for

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Probability of Missile Generation fromLow Pressure-Turbine - MUAP.10005-NP (R0)

Table3.4-1 3.5% Ni-Cr-Mo-V Rotor Steel Crack Growth RAte Deviation from'Calculation

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.Probability, of Missile Generatibn 'from LOW Pressure Turbine MUAP-10005-NP,( (1)

3.4.2 Critical CrackSize

The critical crackdepths were obtained for [ ]of integral rotors by using, therelationship between fracture -toughness and stress intensity, as is done in LCF evaluation inSection 3.3. Critical crack, depths Were determined at running. speed'and design overspeedconsidering stress-diStribution 'change along with the crack prpagat'ion inward.

3.4.3 Numerical Results

Based.on the distribution, andrvariance of crack growth rates and critical crack sizes describedin the previo'us sections;, analyses were. made to determine the probability in a manner that a,Crack would grow to, the critical size within any time interval t. This ;probabilitY of rotot-bursting is.. modified by the number of discs being considered.,

The final probability p•ofiless are, given in terms of discrete'iin~spection i ntervals in Table 3.4-2and are shown in .Figure, 3.4-4. The results show-that-the necessary inspection interval to:satisfy the requirement of missile generation probability lpespthan. 1o&iper year is

even under the conservativeassumptions incorporated into thisanalysis

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Probability2 o:fMissile Generation from LoWPressure Turbine. MUAP-1 0005-NP,(RO)

Table3.4-2 Probability of Missile Generation (per year) due. to Stress Corrosion,Cracking

Figure3.34-1 Probability of Missile Generation (per year) due to Stress CorrosionC racking

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PrO'babiiitv~f fMis sile :Generation fromn Low;.Pres~sUriiýTurbi ne! MULAP-11O005-NP1'R0)

.4.0 DISCUSSION AND CONCLUSIONS

Except for the destructive overspeed mechanism, previous discussions demonstrate that theintegral low pressure rotor design is unlikely to generate .a turbine missile by any of ,themechanisms considered in this cdocument and satisfy the requirement in regard to missile.generation'. The probability of reaching destructive overspeed is primarily dependent uponthe'[ .. Detailed discussion on this matter is addressed inReference 12.

The low pressure~rotors are unlikely to'burst,.as-,a:result of HCF since the maximum alternatingstress on the rotor is less than its endurance, and the safety factors are more than' 3.0.Additional assurances against bursting by thit mechanism are derived from;

1. The locations of maximumi stress in integral rotors, are readily accessible for inspe'tionduring normial maintenance,

2. The, existence 'of a large transverse craak is detectable by high vibrations due. to fiotor,unbalance.

It is reasonable to exclude HCF as a controlling mechanism to-determine in-service inspection,intervals.

Analysis of the LCF mechanism demonstrates that the probability of'failure by thiS scenario is'extremely low! even under conservative assumptions[ I. 'it 'isconcluded that a low pressure rotor rupture can not happen beforef

], and the NRC safety guidelines can be satisfied by the periodic inspection.in a properintervalwithin [

The SCC has the greatest influence on rotor integrity. The probability of failure by thismechanism is however significantly reduced by the application of integral rotor design. Theanalysis shows that a running time ]ay elipse befqre the first inspectionwithout exceeding the NRC safety. guidelines 'even Linder highly conservative assumiiptions,Considering 'the• fact that crack, locations are readily accessible during normal turbineinspections and maintenance, itis concluded from the design view point that the NRC safetyguidelines can be•satisfied by the periodic inspection in a proper interval within [ '.

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Probability of Missile Generation from' Low Pressure Turbine ,M UAP, 10005wNP (R0)

5.0 REFERENCES

1. S. Kawaguchi, R. Yanagimoto, S. SaWada, and T. Ohhashi, "Historical View ofManufacturing Large Mono-Block Rotor F~rgings and Future Outlook", International,Forging Conference 1981, Volume 1, May 4-9, 1981.

2. J. M. Barson and S. T. Rolfe, "Correlations Between KIC and Charpy V-Notch TestResults in the Transition Temperature Range", Impact Testing of Metals, ASTM STP 466,1970, pp. 281-302.

3. Walden, N.E.; Percy, M.J.; and Mellori P.B., "Burst Strength of Rotating Discs",Proceedings of the Institute of Mechanical Engineers,, 1965-66.

4. Peterson, Mochel, Conrad. and Gunther, "Large: Rotor Forgings for Turbines andGenerators", ASME Annual Meeting, November 1955.

5. Robinson, E.L., "Bursting Tests of Steam'Turbine Disc Wheels", ASME Annual Meeting,1943.

'6. P.- C. Paris, "The, Fracture Mechanism Approach: toFatigue", Fatigue -An InterdisciplinaryApproach, Proc. 10 h Sagamore Army Materials Research Conference, Sy'acuseUniversity Press, 1964.

7. H. Itoh, T. Momoo, S'. Tsukamoto," SCC, Suceptibilly of 3:5NiCrMoV Steel. in An ActualLow-Pressure Turbine Environment", ICONE-81 1t3, 2000.

8. F. F. Lyle Jr., H.. C. Burghard Jr., "'Steam Turbine Disc Cracking Experience", EPRINP-2429-LD RP 1389-5, Vo1.1-7, 1982.

9. B. W. Roberts, PR. Greenfield, "Stress Corrosion of, Steam Turbine Disc and Rotor Steels',CORROSION-NACE Vol. 35, No,9,p.402, 1979.

1.0. T; Endo, H. Itoh, Y. Kondo, H. Karato, "Material Aspect for the, Prevention ofEnvironmentally Assisted Cracking in. Low Pressure Turbine", PWR-Vol.21, The SteamTurbine Generator Today: Materials, Flow Path Design, Repair and Refurbishment, 1993.,

11. MUAP-07028(RO)-P, Proprietary and MUAP-07028(RO)-NP, Nonproprietary, "Prolbabilityof Missile Generation from Low PressureTurbines," Revision 0, December2007

12. MUAP-07029(R1)-P, Proprietary and MUAP-07029(RI1)-NP, Nonproprietary, "ProbabilisticEvaluation of Turbine Valve Test Frequency,' Revision, 1, June 2010.

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