ML20006E821

LER 90-002-00:on 900117,review of Cooldown Data Showed That Cooldown Rate of Pressurizer Exceeded Tech Spec Limit.Caused by Procedure Inadequacy.Procedures Revised to Require Use of Water Space Temp to Find Cooldown rate.W/900220 Ltr

ML20006E821
Person / Time
Site:	Prairie Island
Issue date:	02/20/1990
From:	Hunstad A, Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
LER-90-002, LER-90-2, NUDOCS 9002260388
Download: ML20006E821 (4)

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T' February 20, 1990 10 CFR Part 50 Section 50.73

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[~- Director of Nuclear Reactor Regulation i

U S Nuclear Regulatory Commission Attn: Document Control Desk j Washington, DC 20555 PRAIRIE IS1AND NUCLEAR GENERATING PLANT Docket Nos, 50-282 License Nos. DPR 42 50-306 DPR-60 Excessive Pressurizer Cooldown Rate and Excessive Sorav/ Pressurizer Delta-T Caused by Procedure Inadeauncy The Licensee Event Report for this occurrence is attached, 1 Please contact us if you require additional information related to this event.

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/ Thomas M Parker E Manager l Nuclear Support Services i

c: Regional Administrator - Region III, NRC NRR Project Manager, NRC Senior Resident Inspector, NRC MPCA Attn: Dr J '4 Ferman Attachment

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On January 17, 1990, Unit I was shutdown for the Cycle 13 14 refueling outage.

On January 19,.1990, review of the cooldown data showed that the cooldown rate of the pressurizer had exceeded the Technical Specification limit of 200*F/hr, and the teraporature difference between the pressurizer auxiliary spray and the pressurizer had exceeded the Technical Specifications limit of 320*F.

Procedure inadequacy is designated as the root cause of the event.

Pressurizer steam space temperature was used to determine the cooldown rate.

Pressurizer water space temperature should have been used to determine the cooldown rate. The maximum cooldown rate over a one-hour period, for the pressurizer water space temperature was 265*F. Procedures do not explicitly require use of pressurizer water space temperature for determining heatup and cooldown rates. The operators verified that the temperature difference between the pressurizer and the pressurizer spray was less than 320*F using control board indication. Ilowever, a more precise determination of the temperature difference obtained from the Emergency Response Computer System t

indicates that the actual temperature difference was 349"F.

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0 (0 012 at.. . . we w m.unn EVENT DESCRIPTION On January 17,1990, Unit 1 was shutdown for the Cycle 1314 refueling outage. '

On January 19, 1990, review of the cooldown data revealed that the cooldown rate of the pressurizer (EIIS Component Identifier: PZR) had exceeded the Technical Specifications limit of 200*F/hr, and that the temperaturq difference between the pressurizer auxiliary spray and the pressurizer exceeded the Technical Specifications limit of 320*F. These actions were in i violation of Technical Specification 3.1.B.4.

CAUSE OF Tile EVENT Procedure inadequacy is designated as the-root cause of the event. The operators were well aware of the 200*F/hr cooldown limit in the Technical Specifications and in the Unit Shutdown Procedure. They considered the pressurizer steam space temperature to be more representative of the actual overall pressurizer temperature and considered the pressurizer water space temperature to be a more localized indication and subject to transient effects. Therefore, the operators used the steam space temperature to monitor the pressurizer cooldown rate. The pressurizer steam space temperature cooldown rate remained below the Technical Specification limit. The procedures do not explicitly require use of pressurizer water space temperature for determining heatup and cooldown rates, llowever, the thermal ,

stress analysis for the pressurizer lower head and surge nozzle uses 1 pressurizer water space temperature for determining thermal fatigue effects. i The maximum cooldown rate over a one-hour period for the pressurizer water space temperature was 265'F. The Emergency Response Computer utilizies pressurizer water space temperature.

L The operators verified the temperature difference between the pressurizer and L the pressurizer auxiliary spray, was less than 320*F using control board l indication, llowever, a more precise determination of the temperature l- difference obtained from the Emergency Response Computer System indicates that j l the actual temperature difference was 349'F.

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ANALYSIS OF THE EV M I  ;

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This event is reportable pursuant to 10 CFR 50.73(a)(2)(1)(B) since Technical Specification 3.1.B.4 was violated. .

l The occurrence of such temperature cycles causes an increase in the fatigue usage for the pressurizer surge nozzle, the inner surface of the lower head and shell, and for the pressurizer spray notale. Based on the recorded temperature data from this cooldown, the operating history of the unit, and ',

similar evaluations performed for several other plants, it is the judgment of Westinghouse that the allowable pressurizer fatigue life has not 1een  ;

approached, and that the pressurizer structural integrity has not been  ;

compromised. Westinghouse is performing a detailed engineering evaluation, including fatigue and fracture analysis, to determine the specific effect of this type of pressurizer cooldown on the design life of the plant.  ;

CORRECTIVE ACTION ,

procedures will be revised to: ,

1. require use of pressurizer water space temperature for determining pressurizer heatup and cooldown rates; and '

2. require use of the Emergency Response Computer System to monitor the temperature difference between the pressurizer steam space and the g  ;

pressurizer auxiliary spray, whenever possible. l These procedure revisions, will be in place before the next scheduled unit cooldown.

FAILED COMPONENT IDENTIFICATION i

None.

PREVIOUS SIMTIAR EVENTS There have been no previous similar events reported at Prairie Island.

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