ML20081G651

Discusses Plant Specific Thermal Stratification Analysis Results & Completion Date Extension Request for Completion of Action Item 1.d of NRC Bulletin 88-011

ML20081G651
Person / Time
Site:	Point Beach
Issue date:	06/07/1991
From:	Fay C WISCONSIN ELECTRIC POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-91-054, CON-NRC-91-54 IEB-88-011, IEB-88-11, TAC-72155, TAC-72156, VPNPD-91-184, NUDOCS 9106130238
Download: ML20081G651 (8)

Text

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Wisconsin Eik>ctnc POWER COMPANY 5

231 w Menwn Po b ;m Mwee w 5r01 9mm M VPNPD 18 4 NRC 0 5 4 June 7, 1991 U.S. NUCLEAR REGULATORY COMMISSION Document Control Desk Mail Station P1-137 Washington, D.C. 20555 Gentlemen:

DOCKET NOS. 50-265 AND 50-301 ,

PLANT SPECIFIC THERMAL STRATIFICATION ANALYElg RESULTS AND COMPLETION DATE EXTENSION REOUE3T FOR COMPLETION OF ACTION ITEM 1.d_QE NRC IE BULLETIN 88-11 (TACK NOS. '2155 AND 72156).

POINT BEACH NUCLEAR PLANT UNITS 1 AND 2

References:

1) Wisconsin Electric Power Company Letter No.

VPNPD-89-314, dated 05/31/89, to the NRC on the subject of " Submittal of Justificacion for Continued Operation Regarding Pressurizer Thermal Stratification, Point Beach Nuclear Plant Units 1 and 2".

2)_ Letter from the NRC to C. W. Fay, dated 09/25/90, on the subject of "NRC Bulletin No.

88-11, Pressurizer Surgo Line Thermal Stratification - Evaluation of WOG Bounding Analysis (Tack Nos. 72155 and 72156).

3) Wisconsin Electric Power Company Letter No.

VPNPD-90-498, dated 12/18/90, to the NDC on the subject of " Request for Extension of analysis Completion Date per Item 1.d of NRC IE Bulletin 88-11".

In a letter dated December 18, 1990, Wisconsin Electric Power Company (WE) notified the NRC that we would not meet the completion date specified for the reporting requirements in Action Item 1.d of IE Bulletin 88-11 for Point Beach Nuclear Plant (PBNP) Units 1 and 2 (Reference 3). The letter stated that WE had elected to proceed with the thermal stratification analysis independent from the Westinghouse Owners Group (WOG) detailed generic analysis, and that this analysis was currently under way. WE committed to an analysis 910613023G 910607 PDR ADOCK 05000266 .Y l P PDR l

. , i Document Control Dook June 7, 1991 Page 2 j l

completion dato of May 31, 1991 because of the complexity and refinomonta required to completo the analysis. This letter providos a summary of the analysis results to dato, and a request for a revised completion schedulo for the items remaining for fulfillment of all the reporting requirements of the bulletin.

WE was informed by Westinghouso Electric Corporatjon in M1y 1990 that PDNP Units 1 and 2 would not be completely bounded by the WOG generic detailed analysis as documented under WCAP-12639 ontitled "Wostinghouse Owners Group Prosaurizer Surgo Lino Thermal Stratification Genoric Dotalled An31ysis Program MUHP-1091 Summary  ;

Report", dated Juno 1990. The piping configuration chosen for tho l water solid hoatup/cooldown (H/C) analysis group (which is i conservative for PBNP) did not demonstrato codo compliance for pipe i stress and fatigue when the Strosr Intensification factor for the ,

long radius elbows utilized at PBNP were applied to the fivo-diamotor bonds analyzed in the Westinghouse model. Mostinghouse indicated with a high degree of confidence that PBNP would demonstrato code compliance with a plant specific analysis. ,

Pursuant to this notification, WE elected to perform a plant I specific analysis for each unit at PBNP, and applied for an  ;

extension to May 31, 1991 for completion of the reporting  :

requirements in Action Item 1.d of the bulletin.

Tho plant specific analyses have boon completed by sargent and Luady, and incorporato the actual design for each unit at PDNP. [

The detailed analyscs include the as-built system layouts, support design and configuration, pipo fittings and materials, carthquake i design, and all applicable design and stratification transients for the surgo lino piping. In order to maintain conservatism and  ;

consistency with the WOG generic detailed analysis, definitions and I characteristics of stratification, the number of ovents, l magnitudos, and number of cycles used in the analf sos are the samo as the generic definitions and transients developed by the WoG program in-WCAP-12639.  ;

The plant specific design and thermal stratification analysis results demonstrate that the curgo lino is within Codo pipe stress and fatiguo allowables for the 40-year design life of the plant for both Units, with the exception of the Integral Wolded Attachment i (IWA) lug / collar design for PDNP Unit 1 pipe whip rostraints R2,  :

R4, and R5. The attached document entitled " Wisconsin Electric Power Company Point Beach Nuclear Plant Units 1 and 2 Pressurizor Surgo Line Thermal Stratification Analysis Results and Plant Specific Responso for NRC IE Bulletin 88-11" provides a summary of the pipo stress and fatiguo analyses for Codo compliance. The worst cdLo Cumulative Usage Factor (CUF) of 1.901 for the Unit 1

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Document Control Desk June 7, 1991 l Page 3 l 3

IWas occurs at R4, and allows for an additional 37 heatup and

' cooldown sequences before the CUT excoods 1.0. The highest CUF at locations other than the IWAs is 0.755 for Unit 1 and 0.875 for Unit 2 at the reducer to pressurizer safo end wold.

Since the Unit 1 IWAs do not satisfy Code fatiguo requirements (utilizing conservativo analysis techniques), WE will proceed with  !

4 a refined analytical evaluation of the IWAs. If wo determino that

' a modification is necessary to resolve this issue, we will adviso

, you of the installation schedule. We have also determined that it will be necessary to review past operating logs and strip charts to validate the operating history of the plant. From interviews with the operators and proceduro reviews, wo had concludod that tho 210'F Delta-T limit for the water solid H/c method is a i conservativo limit for PBNP. However, a sample chock of the 1989 Unit I hoatup showed that although the system Delta-T was lower  ;

than the 210'F limit, it was higher than the limit previously indicated by the plant operators. WE is proceeding at this time with initiating a further review of past records, and modifying our H/C procedures to assure that the 210'F limit is not exceeded in the future. WE will adviso you of the results of the refined analytical evaluation and our record review as soon as the work is completed. WE anticipato completing those effortn before the end of 1991.

WE has concluded that PBNP can safely continuo to oFarato at full power under the JCO submitted to the NRC in May, 1989 (reference 1). The basis for this JCO was the generic bounding '

analysis performed under WCAP-122'7. The plant specific detailed analyses completed for each urit .t PBNP demonstrate the applicability cf this JCO for coruinued full power operation. The JCO allowed for a maximum of ten Juditional H/C cycles froa the date of submittal in May 1989. PBNP has experienced five H/C <

cycles on tait 1 and two on Unit 2 sinco submitting the JCO. This -

leaves a sufficient number of cycles to maintain an adequate safety margin, and therefore, we conclude that there are no short-term safety concerns associated with thermal stratification offects on the surge lines at PBNP.

This.JCO will allow WE sufficient timo to evaluate whether to apply refined anslytical techniques to the Unit 1 IWA pipe whip rostraint doJigny for Codo fatigue compliance, or to modify the whip restraint designs to eliminate the lug problem altogether.

Additionally, this will allow WE to complete the additional reviews of past operating records, and to revise the PBNP operating procedures to assure compliance with the 210'F system Delta-T limit for water solid heatup and cooldown procedures.

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Document Control Desh June 7, 1991 Page 4 Picano contact us if you have any questions concerning our proposed actions in this manner, very truly yours, L.!

//

g is bl C. W., ray Vice president 11uclear Power Department Copios to: 11RC Regional Administrator - llegion III IJRC Resident Inspector

WIHCONHIN ELECTRIC POWER CONPANY POINT DKACH NUCLEAR PLANT UNITS 1 AND 2 PREDDURIZER DURGE LINE THERMAL STRATIFICATION ANALYDID REDULTD AND PLANT SPECIPIC RESPONDE FOR NRC IE DULLETIN 00-11 Wisconsin Electric Power Company (WE) elected to perform individual plant specific analyses for the offects of thermal stratification on the Point Beach Nuclear Plant (PDNP) Units 1 and 2 pressurizer surge lines to setisfy the requirements delineated in NRC 1E Dulletin 88-11. This decision occurred after being informed by Westinghouse Electric Corporation in May 199n that PDNP wou3d not be completely bounded by the Westinghouse Owncra Group (WOG) generic detailed analysis for the thermal stratification of the pressurizer uurgo line because of the iony radius elbows utilized at PDNP.

A summary of the results of the plant specific analyses performed by Sargent and Lundy are au follows:

1) h PPLIC A D I LI T_Y_O F_DI; p I O N_I H r_QRH ATIO N WE has reviewed the piping layout drawings, support drawings, pipe whip restraint drawings, and all other information provided to the Westinghouse Owners Group (WOG) Ior the generic detailed analysis contained in WCAP-12639 entitled

" Westinghouse owners Group Pressurizer Surge Line Thermal Stratification Generic Detailed Analysis Program MUHP-1091 Summary Report", dated June 1990 and has concluded that the generic c'etailed analysis and design basis information is applicabls for PbHP units 1 and 2,

2) YE RI rlRATION_OF_Q PE RATIO N A L_M l;T110 D0 2.1 WE has determined irom a review by the PUNP operations department, and prior surveys by the WOG that PDNP follows a water solid heatup/cooldown method for both units and have determined that the maximum system AT of 210*P is within the limits set by Westinghouse in its generic detailed analysis, and utilized by Sargent and Lundy in their plant specific analyses for heatup, cooldown, and RCS venting.

2.2 Additional review of the operating procedures has determined that the maximum RCS temperature during the venting operation is limited to 200*r, at which temperature the RCS is utill water solid and the system AT is less than 150*F.

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3) RU P P.0RT_ LOAD R_AND_PI PI NQ_D10 P L AC E M ENT O 3.1 The nurgo line piping in nupported by throo variablo opring hangers per unit at PUNP. Thero are no rigid rentraints on the surgo lino piping for either unit.

Individual spring can settings woro used in the analyoun 30 required for each respectivo opring can.

3.2 The plant specific analysis piping displacomonts for all normal design conditionn, atratification effects, and thermal anchor displacements of the RCL and pZR at each apring support and whip rostraint location were compared to the available travel distances and gap dimensions respectively. The analyzed piping displacements for the spring hangers were all within their respective travel distances. There were soveral insulation hits on Unit 2 that required ovaluations for gap closuron. The results of thoso ovaluations show that the insulation gap clonures woro of a small magnitude t.nd an a result have a negligible offect on the global piping responso and stresses.

Thoro was one metal-to-metal gap clocuro on pipe whip restraint R4 on U1. This interforence was caused by normal thermal growth of the piping and was previously evaluated and found to be acceptable for stroscos, loads, and fatigue. This analysis (reference 1) had already boon completed prior to the plant specific analyala, and the offects of this interforence were accounted for in the thermal stratification analynia.

4) RElBMLC_AND_DKhDMRIORT_KQMENTD 4.1 WE has compared the OBE pipe bending moments used in the WOG fatiguo analysis (WCAP-12639) with the maximum of those which have boon analyzed for both PDNP units. The i results are tabulated below MOMENT _(fl-LD1 EITIING ANALYSID Mb Mt Isng radius elbown WOG 34000 34000

" S&L 7300 (U1) 10100 (U1;

" S&L 6100 (U2) 10600 (U2)

All other components WOG 60166 60166

" S&L 12300 (U1) 3000 (U1) l

" S&L 12100 (U2) 3000 (U2) l 4.2 WE hwa compared the equation 13 allowable doadweight and ODE' mismic resultant moments for the RCS hot leg nozzlo calt.ulakod in WCAP-12639 with those generated in tho analysen for each Unit. The results of this comparison cro es follows:

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EITTING ANhhYDID REQMLTANT_MQMENT_(ET-LDL RCS hot leg nozzle WOG 36700

" S&L 12900 (U1)

" S&L 16000 (U2)

5) MX IMUM_.QOM EETID_DERG E _kI NE_EI EI NQ._STRE R R E E The maximum computed stresses for both the primary stress intensity and primary plus secondary stress intensity are summarized below:

MAXIMUM ALLOWABLE STRESS STRESS ,

EQUATlDll DU111 1)Uill LOCATLQ11 t IM11 (U?) >

9B 8.9 9.1 24.75 Red. Le Safo End l 9D 9.8 10.1 36.6 LRE near RCL 10 60.9 u9.1 49.5 LRE near RCL 12 44.5 52.6 54.9* LRE near RCL 13 34.3 22.7 49.5 LRE near RCL

• Allowable based on average value of Sm, (Smi + Smj)/2, where

i and j are the load sets producing the maximum thermal stress range.

6) MAX 1MUR qQMEUIED CUMULATIVE U8h0EJACIQRS The maximum computed cumulative usage factors (CUF) developed by the plant specific analyses for each unit are as follows:

LOCATION UNIT CMI Reducer to PZR Safe End 1 .755 (1)

Reducer to PZR Safe End 2 .875 (1) Maximum value at locations other than those with integral welded attachments. See Section 7.0 for results at these locations.

7) KYAhUAT_LON OF INTI_QRAL WELDED _ATIACEMENTR PBNP Unit 1 has three integral welded attachments (IWAs) at pipe whip restraints R2, R4, and RS. The lug / collar design is

! the same for each restraint. Because the lugs are only wolded to the top of the pipe, thermal striping effects on the lug CUF were ignored.

EQ. 10 STRESS CUT (1) (3) TOTAL H/C ltEST. Not Dutil H/9_ LUG Fil&G IN1: RILL 21 R2 25.6 .489 1.385 144 R4 30.1 .503 1.901 84 R5 27.9 .470 1.454 137 (1) Basad on 40-year H/C design cycles (2) Number of H/C event sequences for which CUT s 1.0 in the present configuration (3) The maximum usage factor at locations removed im the lug locations is; cur =0.755 The IWAs exist only on the U1 surge line as part of u.ie existing pipe whip restraint lug / collar design for R2, R4, and RS. R4 was previously evaluated for metal-to-metal gap closure (reference 1) due to normal thermal operating conditions and found to be acceptable. This condition was accounted for in the fatigue analysis performed for the lugs.

Code case H-122 was conservatively used to evaluate the IWAs.

The results indicate acceptable fatigue usage for the 40-year design life of the unit assuming the average current rate of 2 H/C cycles per year, but do not demonstrate CUFs less than 1.0 f' 'ho full 200 H/C design cycles. WE is currently eva.uating whether to use further refined analytical techniques to satisfy Code fatigue requirements or to modify the whip restraint design to climinate the IWA design. We expect to have this evaluation completed before the end of 1991. If we determine that a modification will be necessary to resolve the issue, we will advise the NRC of the schedule for installation of the modification.

8.O EYAkMATLQH_QLEREDDRRHEJLEQMkB The pressurizer surge nozzle loadings due to normal operating, seismic, and thermal stratification effects have been compared to the previously qualified PZR surge nozzle umbrella loads in the PZR stress report. The qualified umbrella loads are based on a safe end material with lower allowables than the PBNP PZR safe end material, and are transmitted by a 10 inch diameter pipe instead of 14 inches as used in the report. The worst case forces are less than 15% of the umbrella force allowab)es, and worst case moments are less than 65% of the umbrella bending moment allowables. Therefore it is deemed that the loads generated by the plant specific analysis (including thermal stratification effects) on the PZR surge nozzle are acceptable.

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