ML20059G739

Accepts Util 890601 & 1218 Responses to Item 1.b of Bulletin 88-11, Pressurizer Surge Line Thermal Stratification. Certain Issues Must Be Resolved Before Plant Meets All Appropriate Code Limits for 40-yr Plant Life

ML20059G739
Person / Time
Site:	Crystal River
Issue date:	09/06/1990
From:	Silver H Office of Nuclear Reactor Regulation
To:	Beard P FLORIDA POWER CORP.
References
IEB-88-011, IEB-88-11, TAC-72172, NUDOCS 9009130123
Download: ML20059G739 (3)

Text

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. UNITED STATES q

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NUCLEAR REGULATORY CGMMISSION

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iL WASHINGTON, D. C. 20655 p,

September 6L1990; L

Docket No. 50-302.

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'Mr. Percy M. Beard $ Jr.

Senior Vice President,.

Nuclear Operations Florida Power. Corporation.

~ ATTN: Manager, Nuclear Operations 4

Licensing.

P. O. Box 219-NAL21 Crystal River,iFlorida 32629

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SUBJECT:

CRYSTAL RIVER UNIT 3 - NRC; BULLETIN NO. 88-11. " PRESSURIZER SURGE h

LINE THERNAL STRATIFICATION" - EVALUATION Of BABC0CK AND WILCOX 1

OWNERS GROUP BOUNDING ANALYSIS'(TAC NO. 72172)

By letters dated June-1,1989 and December 18, 1989, you responded to Item 1.b-of NRC Bulletin No. 88-11 " Pressurizer Surge Line Thermal Stratification."

a' These letters stated that a bounding analysis performed by the Babcock &.

Wilcox 0wners Group (B&WOG). indicated that the. pressurizer surge -line (PSL) may not satisfy the ASME Section III Code criteria.for the 1ife of the plant, taking into account the effects of thermal stratification. The analysis did, however, state that the integrity of the PSL was adequate to = justify-continued operation of the faci.11ty for several years..

The staff has completed its review of the B&W9G bounding: analysis and find's.

that sufficient infvmation has been provided to justify continued plant operation until Cr3 Cil River 3 con.pletes its final report in accordance with l

the schedule delinea a d by the Bulletin;.however, there are~ issues that need to be. resolved before the staff can conclude that the.PSL meets all appropriate Code limits for 40-year plant life. A copy of the evaluation that was-sent to l

the B&WOG is aaclosed for your information.

You are encouraged to work. collectively through the B&WOG to address the issues

-identified in the evaluation, but Florida Power Corperation should ensure that the actions requested by the bulletin ere implemented at-Crystal River 3.

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SeptemberJ 6(1990,

'Mrf P. M. Beard o

1 The staff will assess the conformance of she' PSL-to applicable Codes a' d' i

n regulatory requirements: for 40. year.. plant'.11fe whenithe B&WOG report regarding Item l'.d of the Bulletiniis' submitted.

j Sincerely, 1

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Originalisigned'by i

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Harley Silver, Project Manager ?

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Project Directorate II-2i y

Division of. Reactor / Projects. LI/II.

Office of Nuclear Reactor Regulation 1

Enclosure:

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'0FFICIAL RECORD. COPY Docunant Name:

CR3 BULLETIN 8811 t

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i (Mr. Percy M. Beard,' Jr.:

Crystal River Unit No. 3 Nuclear Florida Power-Corporation Generating Plant:

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Mr. A..H; Stephens State Planning and. Development 1 General Counsel.

Clearinghouse Florida Power Corporation MAC - ASD-Office of Planning and Budget i 4

Executive Office-of the Governor-

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P. 0. Box 14042 The Capitol. Building a

St. Petersburg, Florida 33733:

. Tallahassee,-Florida 32301.

Mr. P. F. McKee, Director.

Chairman-Nuclear Plant Operations 1

Board of County Comissionert Florida Powr Corporation!

Citrus County '

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-NA-2C' 110 North.Apopka Avenue g

Crysta;

ver,- Florida 32629 Inverness, Florida 32650.

Mr. ' Robert B. Borsum Mr. Rolf C. Widell, Director?.

Babet ck & Wilcox

-Nuclear'0perations.SiteLSupport' Nuclear Power Generation Division Florida Power Corporation 1700 Rockville Pike, Suite 525 P.O. Box 219.HA-2I Rockville, Maryland 20852<

Crystal. Rive

'orida 32629 Senior' Reside.t Inspec'.or.

Mr. Gary L.

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Crystal River Unit 3 Vice President, Nuclear Production.

U.S. Nuclear Pegulatory Comission Florida Power Corporation.

15760 West Powerlina Street P. O. Box 219-SA-2C Crystal Rive, Florida 32629 Crystal River, Florida 32629 Regionti Admi,11strator, Region'II U.S. Nuclear I:egulatory Commission 101 Mar 1etta Street N.W., Suite 2900 Atlanta, Georgia '30323 Mr. Jacob Daniel Nash Office of.'lediation Control Department of Health and Rehabilitative Services 1317 Winewood Blvd.

Tallahassee, Florida 32399-0700 Administrator Department of Environmental Regulation J

Power Plant Siting Section State of Florida 2600 Blair Stone Road

'Tallebassee, Florida 32301 l

Attorney General l-Department of Legal Affairs The Capitol l

Tallahassee, Florida 32304 l

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,1 B E Knclosure

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F ENCLOSURE-l1 REVIEW 0FL L 8ABC0CK AND WILc)x OWMTS' GROUP fB&WOG?

1

' PRf55URIZER 50RGE L INE THERMA, STRATIFICATION

-BAW-20B5 DATED MAY 1989 l

INTRODUCTION The pressurizer surge.line (PSL) in thel pressurized water reactors' l-(PWRs)..is'a-stainlesssteelpipe connecting the bottom of the

- pressurizer vessel to the hot leg,of one of the coolant loops.. The out flow of the pressurizer water is generally warmer than the hot 1eg flow.

Such temperature differential (delta T)! varies with plant operation S

activities and can exceed 400*F during the' initial plant heat-up. -

Thermal stratification'is the separation-ofLhot/ cold flow stream in;the horizontal portion of the PSL resulting in a temperature differenceL the-top-and-bottom of the pipe.- Since thermali at' stratification is the direct results of the differences;in; densities betweenf the pressuriter ;

and the hot leg water, the pottential:for stratification is increased as system delta T increases and as the insurgeL or outsurge flow decreases.

Stratification in PSL was found recently and confirmed by datac. 9 red from several PWR plants.

Original design analyses of the surge line'did not include 1any stratified flow loading conditions.' Instead it assumed complete sweep of fluid;along.

the line during insurges or.outsur at any particular piping location.ges resulting in uniform thermal loading-Such' analysis did not. reflect'PSL actual thermal condition and potentially may overlook undesirable line deflection and its actual strasses may exceed design limits. =In addition.

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the striping phenomenon, which is the oscillation'of the: hot:and cold.

wall, needs also to be analyzed. Thus assessment of stratif effects on PSL is necessary to ensure piping integrity and ASME Code Section III conformance.

STAFF EVALUATION Since stratification in PSL is a generic concern to all PWRs. an NRC Information. Notice No. 88-80 was' issued on October 7 NRC Bulletin 88-11 for the same concern was also issu 1988, and then an Babcock & W.1cox-(B&W) ed on December 20, 1988.

generic bounding evaluation re.-on behalf of the B&WOG, has performed a.

of presentation material and explanatory text.portBAW-2085(Reference L

which consists Additiona also provided in Reference-2.

The purpose of the report is to:

Describe the 88WOG program and plans for addressing the surge Ifne a.

thermal stratific tion and striping issues.

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Present:the results of the prelimir.ary work done,to date,to justify ~

1 continued operation-(JC0) until the finaliprogram results are available.;-This=is expected-to be completed by December 3 !

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B&W reportid that:the thermal-striping' program has not bee' n' completed y u

and onlyl preliminary results are available.

Upen completionfo* the?

' technical basis for~ the 40' year licensed life of the pl 4 s of calculated PSL thermal displacements with the Oconee 1 measured data

! will also-be performed in the final report.

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x The follr. wing is the staff'sfevaluationiof 8&WLefforts and information; provideO in references >l and 2.

(M-K)g N

hs hot functional'.testitof the'B&W1 Durin plantist Muelheiu Kaer11c'h' were taken during start-up which confirmed that' strati in,the.PSL. cL a result, B&W defined a program to: instrument one of!the domestic, plants;to'determiae magnitude-of. stratification effects.since-the.M-K' plant is different from the' domestic plants in terms ofL power.

level, PSL layout, pipe ~ diameter and thickness.

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Later the scope of the program was expanded to include sur movements as well as data for evaluating thermal < striping.ge Ifne i

Based on the M-K data, B&W concluded'that the. Surge Line stratification-depends on the following factors:

Surge Line Flow' rate and flow direction.

a b

Cooling of the fluid (ambient loss).

Boundary thermal conditions (Hot Leg and Pressur12erctemperatures).

c SinceallB&Wdomesticplants(7-plants,10 units)-ha'ethesa L

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-bounding fatigue ev,aluations:-

a.

Oconee 1 b.

Davis-Besse TheDavis-Besseplantsur!alinehasalonghorizontalrunfromtheHot Leg to a 7.25 foot vertic 1 drop near the center of the' surge line span ^

to another long horizontal run of pi n which connects to the bottom of the pressurizer.

Hence the overall run of the pipe is essentially divided into two horizontal runs by the 7.25 foot verticalisection.

This vertical rise near the center of the surge line will reduce transmission of the stratification gradients downstream.

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In allither plants a'13 foot vertical; drop of pipe. exists much closer to 1

the hot leg resultingin a-very short horizontal section:of 21 inches ennnecting to-the hot:1eg nozzle.

This results in a'different surge' line routing at Davis-Besse,-therefore, two ssparate fatigue evaluations were performed.

l-L, 140 S.S. pipe.

The= surge line for each configuration-is 10'/ schedule.

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The Oconee l' surge line was modeledlusing.the computer code. The loadings consisted of-pres.ANSYS finite element.

sure, seismic 1

thermal expansion; from;the original stress report, and were. deadweight, and L

combined with the new~ thermal stratificationtloads.

The temperature ranges used were obtained from the'M-K measured deta -since no plant specific: data were available at the time of the bounding evaluation.

Thermal stratification was' assumed to occur over the entire lower-

1 horizo three.ntal run of pipe.. The maximum pipe top-to-bottom delta T, for:the; j

load cases considered, pre-heatup. heatup, and cooldown. was assumed to be 330'F 422*F:end 306'F respectively, and it was based on the i

maximum systemidelta T.

during each cycle.-

Pre-heatup was assumed to occur.three times Stress indices in accordance with ASME III 1977. Edition with Addenda through ths-Summer of 1979 were used.

The Oconee 1 bounding fatigue' evaluationLpredicted expansion stresses for equation 12 which occurs on the vertical elbow from the pressurizer, is far in excess of the ASME Code allowable limit of 35 =50.1 ksi-(or twice the material yield strength),atT=650'F. EqEationi9and13stressesarewithinCode allowables since they are not impacted by thermal stratification.

To take. advantage of the material behavior in the inelastic range, B&W substituted the cyclic " strain-hardended" yield strength ($ ), in place i

of the static yield strength (S

.andahigherallowablevIlueof25 was obtained. The Si value is de) fined as~ the " strain hardended strength of the'mateFial at temperature.

Bf,W reported that in the final analysis, it is their intent to meet the ASME Code acceptance criteria of section NB-3600.

The staff disagrees with this approach of using~twice:the "itrain-hardened

• yield strength in place af the code specified 35, limit even if this is a preliminary and conservative analysis.

With the exception of Davis-Besse, all'other plants have no rigid supports or whip restraints. Even if the Oconee 1 type plants have no supports which resist thermal motion there is no-indication that snubber / spring travel limitations wer,e considered in the bounding l

The staff's receraendation is that thermal motion of PS!.

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evaluation, needs to be considered at the support locations and verified that q

adequate snubber / spring travel exists.

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Pagel4:of:7 tg The fatigue usage factors for Oconee IJ type plants e

effects, were calculated at several locations along, excluding.the ' striping '

I the surge l1ine for '

the thermal stratification load' cases ar.d.were combined with those,;fromi c

, the stress-analysis'of record tof obtain;the total: usage factor.

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Basedton the fatigue life of each part affected by theistratificationw..

W,J effects,1the allowable number of heat-up/cooldown cycles was n1culated.:

R Location Allowable number:

of cycles 1

Hot Leg nozzle C.S.: portion)

Surge.pnozzle-((5.5. Portion))-

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'q Surge 'line drain nozzle--

153 135 Pressurizer nozzle (S.S. portion)

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Pressurizer nozzle (C.S. portion) q 3g6-o This indicates that, the worst case plant Oconee 2 3h;ch has experi '

enced 96 cycles to date, can withstand an,additiona! 39 cycles to reach the allowable limit of 135 cycles for the" Surge:11ne drain nozzle or e C.U.F.=.71(96/135).

striping.-

The.71 factor does.not include the effe, cts 'of Based on the average' of g cycles / year BR indicated that an additional 4 years of' continued plant operation can be justified.+

L The Davis-Besse surge line analysis was conducted int a similar manner as the Oconee Unit 1 analysis. ' The design' transient inputs-for~.the fatigue i

analyses were developed by Toledo Edison.

Adjustments were made to the M-K data to account for the differences between M-K'and' Davis Besse but n L

plant-specific temperature distribution. data or surge line displacements were obtained.

Thermal straification was assumed to occur over the full length of the lower horizontal pi;4 run and each transient was assumed to occur three?

times during the buable formation.

1 The staff concludes that furtheri investigation is necessary to justify this assumption for theLDavis-Besse.

l type plants.

The staff also feels that, depending-on'the. direction of.the

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flow (insurge or outrqe), thermal stratification may occur in the upper s;

L horizontal run of rig rnd that the Davis-Besse unique configuration will it experience differer.t antification conditions than the Oconee 1 type plants. -

i For Davis-Besse 1,

1. 11 Corporation performed the deflection / stress 1

analysis of the thermal stratification events using the ANSYS computer t

code and the surge line met the 35, limit of the 831.7 Code for equations 10 and 12.

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m page 5 of 7) c The 35" limit'was based on values from'the Certified Material Test Reportse'

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(CMTR)

Due to;the uncertainty of. the relationship between product strength H

-and the CMTR values

' Code allowables is,n.- it is obvious' that the use of, such values for, replacing g

ot acceptable.:

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.88W performed the' bounding fatigue evaluation utj Location C;U.F.

Hot leg nbzzle branchconn'ction) e 10.619 Hot leg Aozzle C.S. Portion)

-.0.704 Hotle9 nozzle-S.S. portion))

Surgeiline-(Straight or elbow

-0.343 1

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0.0631 Pressurizer nozzle (S.S. portion)

0.297 Pressurizer nozzle (C.S. portion)

.t 0.634-i 1

Davis-Besse during the-past~12 yearsBased on the average of:3 c

. years:of. continued plant operation ca,n be assured.,B&W reported that an addition j

1 Subsequent to the' bounding evaluations discussed above temperature-measurements were obtained during the-February 1989 hea,t-up_of 0 cones o Unit 1,'and indicated much smaller pipe: top-to-bottomidelta T. ' Asia result of the PSL temperature measurements, the bounding fatigue: evaluation was reviewed for consistency.

The! measurement program initiated at Oconee and steady. state operation. Unit I determined surge 11ne temperatures

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l bounding evaluation of delta T=422'F and delta T=330'F were foun envelope the actual delta 'T's'of 3 delta T=280*Fiandl delta T=250'F-3 respectively at most critical locations.1 No upsets or complete cooldowns; have occurred yet therefore, measurements for these types of transients ~

1 are not available,to integrate into the bounding evaluation.' Temperature-data were also obtained at the outside' surface'of:the'surgeline.and detailed heat transfer analyses 'were necessary to approximate the conditions at the inside surface to adequately' evaluate the' striping phenomenon.'.

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To account for the effects-of theLnon-linear temperature profile and the lower pipe top-to-bottom delta Ts which were obtair.ed by theitemperature measurements, the peak stress rang,es-calculated in the bounding analysis-

. were refined as follows:

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Scaled down in accordance with the lower top-to-bottom delta T's.

.1 2)

Increased by a factor to account foie the increased pi l-due to the non-linearity 'of the' temperature profila. pe rotation-(Thisfactor is based on a Finite E1erent analysis comparing' actual measurert temperature profile versus assumed linear temperature profile)..

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'. Added the corresponding therma 1' striping peak striping peak stress.

Based on the above refinements-.

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predicted that the worst.compon. the resulting alternating stress range l

ent for the 0 cones Unit 1 PSL drain l'nei o

nozzle can still withstana the limiting number of 135.hiat-up and.

cooldown cycles, as p edicted by.the bounding evaluation.; Similarly tha.

r Davis Besse PSL Hot Leg erzzle cat still-withstand the limiting nunter of

57 heat-up. cocidown cycles.

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evaluated yet and-to accountLfor the thermal; striping offa

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input from too.0conee Unit 1 measurement program will be utilized.

Thermocouples were installed:around theLoutside circumference at g '.

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. locations.along.the surge line.: Heat' transfer analysis will be performed inside surface of the-pipe.to' determine fluid temperature. amplitude and These data will b'e evaluated and a more detail striping fatigue analysis will be performed based on the^ evaluation of the Oconee 1' measured data c

. in10ecember 1990. An' interim assessment of the cyclic t

1

'due-to striping has been made.

Preliminary results from.this striping-

evaluation indicate-that the fatigue impact on<the surge line ist approxi--

mately 101 of the allowable usage factor with the maximum contribution-occurring:during-the early parts of plant heat-up.

1 Based on the information available from the;public domain (BWR feedwater 1,

nozzle tests, liquid metal fast Breeder. Reactor tests,t Argonne National.

4 Laboratory: tests, HOR project. tests), the oscillatory behavior of;the 1

fluid at the stratified interface was selected. 0coneentest data'alsoi l

phenomenon. supports this interim set of characteristics for assessing:the striping

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l CONCLUSIONS q

1 Based on ~our review, we conclude that the informaifon-provided by Babcock and Wilcox in references 1.and 2 is inadequate and not entirely acceptable l

for justifying plant life operation. The-staff concludes that further 1

technical: basis to meet the ASME Code acceptance criterfa~of NS-3600 is-required.

1 1

Concerns that the staff has are the following:

)

a)

The ASME code-acceptance criteria of section NB-3600, Equations g-14 need to be satisfied as applicable. The approach of using twice the

" strain hardended" yield strength or using.the CMTR values in place of the code specified timits may be non-conservative and is not acceptable.

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b) :All supports. includingipipeiwhip restraints,~be considered for the effects of providing thermal conctraint in_the bounding evaluation.

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All-supports, including pipe whip restraints, require plant' specific confirmation of-their capabilities, includin thc/ fall;within the bounds'of the analysis.g clearances and that d);

Comparison:of. calculated PSL the6aal displacements with the Ocone measured data to demonstrate the validity.and~ conservatism of'the:

j bounding. analysis.

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.l, REFERENCES 1).

Babcock and Wilcox report, BAW-2085.. l" Pressurizer Surge Line

(

Thermal Stratification" dated May 1989.

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2)-

Babcock and'W11cox51stter from Daniel F. Spond:to TerencelL. Chan (NRC),06-854.

" Pressurizer S dated September, 29, 1989..

. urge Line Therma 1' Stratification"

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