ML20029A329
| ML20029A329 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 02/12/1991 |
| From: | Parker T NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-011, IEB-88-11, NUDOCS 9102190118 | |
| Download: ML20029A329 (6) | |
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Northem States Power Company 414 Nicohet Matt Minneapohs, Minnesota 55401 1977 Telephone (61?) 3M5500 February 12, 1991 NRC Bulletin 88 11 U S Nuclear Reguintory Commission Attn:
Doewnent Control Desk Washington, DC 20555 PRAIRIE ISIAND NUCLEAR GENERATING PLANT Docket Nos. 50 282 License Nos. DPR 42 50 306 DPR-60 Response to NRC Bulletin 88 11 Pressurirer Surge Line Tlernal Stratification t
References:
1)
Westinghouse Owners Group Letter 00 90 68 to Utilities, dri t e d November 28, 1990, Summarizing November B 9, 1990 Presentation of VCAP 12639 to NRC 2)
NRC Letter to Northern St.ates Power Company, dated Augur.t 30, 1990, with SER on WCAP 12277 3)
Westinghouse Owners Group Letter 00 90 40 to NRC, dated August 3, 1990, transmitting WCAP 12639 4)
Westinghouse Owners Group Pressurizer Surge Line Thermal Stratification Generic Det ailed Analysis Program MUllP 1091 Summary Report, VCAP l639, June 1990 5)
Westinghouse owners Group Bounding Evaluation for Pressuriner Surge Line Stratificatfor. WCAP 12277, June 1989 6)
Northern States Power Company Letter to NRC, dated Mny 25, 1989, Pressurizer Surge Line Thermal Stratification Justification for Continued Operation
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The purpose of this letter is to provide information regarding the status of activities taken by NSP in accordance with Action 1.d of the Bulletin.
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Bnekground l
In order to address the issua of pressuricr r surge line thermal stratification and respond to NRC Bulletin 88 11, the Westinghouse owners Group implemented a program to generically evaluate the effects of stratification on surge line kbi ;
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USNRC No,%wn Mates % %npany February 12, 1991 Page 2 of 5 integrity (Ref. 5).
This bounding evaluation cortpared Westinghouse owners Group plants to those for which detailed plant specific analysis had been performed.
binee this evaluation provided less than full design life verification, a generic justification for continued operation was developed for use by each of the Vestinghouse Owners Group plants.
This justification for continued operation was reviewed and accepted by the NRC staff (Ref. 2) for Prairie Island.
Subsequent to the bounding evaluation and generic justification for continued operation, the Westinghouse Owners Group perfornied a generic detailed analysis on groupings of plants based on their sirnilarity of response to thermal stratification (Ref. 4).
This report was reviewed by the NRC and accepted for reference by Westinf, house Owners Croup plants in n review conducted by the NRC in Pittsburgh, November 8 9, 1990 (Ref. 1),
r frafrie Island Unit 1 Plant specific analysis is being done for Unit. 1, since the Vestinghour.e Owners Group generic program work summarized in WCAP 12639 did not demonstrate acceptability.
The utsting generic justificat ion f or continued operation has been re evaluated and verified that it remains valid.
The Vestinghouse Owners Group detailed analysis was coropleted in July and URC review occurred in November 1990.
Although the Unit 1 plant specific analysis being done by Westinghouse was initiated prior to Novcinber 1990, cottplet ton could not be planned until NRC feedback on the detailed analysis was obtained.
As discussed at the meeting with the NRC in Pittsburgh, we are providing the status and schedule for completion of on going work.
Preliminary results of the NSP program indicate that ASME Section 111 stress and fatigue requirements can be niet for the design life of Prairie loland Unit 1.
These results are contingent on making rnodifications tu pipe whip restraint gaps based on analysis utilizing Icak before break technology.
Modification of pipe whip restraint gaps (subsequent to NRC acceptance of the Leak before break demonstration), as opposed to iterative methods of reinoving further conservatisms from the stratification analysis, was determined by NSp and Westinghouse to be the more technically prudent and cost effective means to effect fatigue qualification of the Prairic Island Unit I surge lino.
Specific details of the program and related schedule are described below.
l 1.
l Plant specific applicability analyses have been performed, including, Global analysis representing configurations before and after whip a.
restraint gap rnodifications.
Resulting support loads and displacements are under review by NSP.
b.
Transient development utilizing monitoring data from ten plants, including Rewaunne (which is similar in design to Prairie Island 1.,
and past operating records for Prairie Island 1 to determine system AT exceedances of 320*F.
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USNRC February 12, 1991 Page 3 of 5 c.
Strest and fatigue evaluations, accounting for global loadings resulting from two configurations, before and af ter the whip restraint gap modifications.
Preliminary resvits of these evaluations show ASME Section 111 Equation 12 stress to be acceptable for the post modification configuration, and the fatigue usage factor value to be within the ASME allowable for design life of the plant.
2.
The pressurizer surge nozzle stress and fatigue evaluation for thermal stratification loadings is in progress.
3.
To justify the pipe whip restraint gap modifications, Leak before break evaluation of the Prairie Island 1 surge line is in progress, sing the loads resulting from the global analysis.
After completion of this program, NSP plans to submit the results of the Leak before break evaluation for NRC approval, to support the modification.
4 The pipe whip restraint gap modifications are planned to be completed during the Prairie Island Unit i refueling outage scheduled for the fall of 1992.
5.
For the interim period untti modifications to the pipe whip restraint gaps are made, the results of the Westinghouse Owners Group generic detailed analysis. (Ref 4) and the generic justification f or continued operation (Ref. 5) apply.
CURRENT STATUS FOR PRAIRIE ISLAND UNIT 1 SURCE LINE STRATlflCATION PLANT SPECIFIC ANALYSES AS OP 0?/12/91, SCilEDULED IMI
.C0titllT103 1)
Final Stress and Fatigue results complete 2/6/91 2)
Pressurizer Surge Nozzle Stress and ratigue complete ?/6/91 Evaluation 3)
Leak Before Break Evaluation A)
Assessment complete 2/6/91 B)
Calculations Complete 2/15/91 4)
Draft Reports A)
Stress and Fatigue Evaluation complete 2/6/91 B)
Leak Before Break Evaluation 2/15/91 5)
Final Reports for ASME and Leak before-break 3/30/91 Evaluations
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P""I USNRC February 12, 1991 Page 4 of 5 Trairle Island Unit ?
Analysis done by the Westinghouse Ovners Group program summarized in WCAP.12639 (Ref. 4), demonstrated acceptable ASME Section 111 Equation 12 stress and fatigue usage in the surge line and reactor coolant loop nozzle for Prairie Island Unit 2.
In this Vestinghouse Owners n oup rep rt, Unit 2 is r
identified as plant number 30 in plant group 11.
NSP had Westinghouse perform additional evaluations in order to further vetify the applicability of the generic detailed analysis specifically for Unit 2 and the results are summarized below.
1.
Review of Past Operating Records Summaries of staximum system AT per heatup and per cooldown were reviewed.
These were compared against the basis for transients developed for plants which use steam bubble methodology, with a maximum system AT of 320'F.
The comparison showed that no exceedances of 320*F wystem AT occurred for past operation of Prairie Island Unit 2, and that the transients used in the Westinghouse Owners Group analysis are applicable.
2.
Verification of Operational Methods Prairio Island Unit 2 does not operate and has not operated such that reactor coolant system venting is performed with a system AT of more than 150*F.
This further confirms the applicability of the Vestinghouse Owners Group transients.
3.
Plant Specific Piping Analysis for Support Loads and Displacements Support loads and piping displacements from the existing thermal analysis performed under the Westinghouse Ovners Group program have been reviewed by NSP and acceptability has been confirmed, 4.
Applicability of Assumed Seismic Moments Seismic Operating Basis Event and deadweight moments assumed in the Westinghouse Owners Group analysis, as specified in Section 9 of Reference.4, vote compared against plant specific values, and were shown to be applicable with respect to the fatigue evaluation.
5.
Evaluation of Integral Welded Attachments The Prairie Island _ Unit 2 pressurizer surge line does not contain integral welded attachments (lugs, plates, etc.).
6.
Evaluation of Pressurizer Nozzle Detailed ASME stress and fatigue evaluations for the pressurizer surge nozzle vera performed, using thermal loadings developed from Westinghouse
Northern Statea Power Company USNRC Pebruary 12, 1991 Page 5 of 5 Ovners Group program data in conjunction eith Prairic Island Unit 2 historical operating data.
Results of these analyses shovtd that the surge nozzle satisfit-s the stress analysis requirements
,1 the ASME Code, Section Ill.
These results are swmarized as follows:
Pl. + Pb 4 Q Stress Intensity Range - 45.6 kai M 1owable Stress Limit - 3Sm - 57.9 ksi Patyue Usage < 0.2 Based on the above summaries, the results of the Reference 4 Vestint, house Ovners Group evaluat: on apply specifically to Prairic Island Unit 2, tind show stress and fatigue aaceptability of the pressurizer surge line for the offects of thermal stratifictition for the design life of the plant.
Please contact us if you have any questions related to our respont.c.
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1111A0 $14 Thomas M Parker Manager fluclear Support Services c: Regional Administrator Region III, NRC Senior Resident Inspector, NRC NRR Project Manager, !!RC J E Silberg Attachments:
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1 UNITED STATES NUCLEAR RECUIATORY COMMISSION i
NORT11ERN STATES POWER COMPANY PRAIRIE 151AND NUCLEAR CENERATINC PLANT DOCRET No. 50 282
$0 306 PRESSURIZER SURGE LINE THERMAL STRATIFICATION Northern States Power Company, a Minnesota corporation, with this letter is submitting information requested by NRC Bulletin 88 11, This letter contains no restricted or other defense information.
NORTHERN STAT.'P W MPANY By-
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'T65 mas M Parker
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Manager,-Nuclear Support Services on this 4f day of_.?
avb/s////beforemeanotarypublicinand.forsaid
- County,personallyappeared7fomas-MParker, Manager,NucientSupport-Services, and being' first duty sworn acknowledged that ho is authorized to execute this document on behalf of Northern States Power Company, that he knows the contents thereof, and that to the best of his knowledge, information, and belief the statements made-in it' are true and_that_lt is'not
- interposed _for_ del y.
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MARCIA K La(XM l [
NOTARY PUBLIC--MINNESOTA i
HINNENN COUNTY S
l My Commussen Lores Sept 24.1933Q i-e m W W W W Wo w W W W W W WW W w r:a i-l
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