ML17312B675

Provides Notification of Error Discovered in Use of Acceptable Large Break LOCA Evaluation Model Which Calculate Cooling Performance of Eccs.Error Led to Less Conservative Values of Peak Cladding Temp

ML17312B675
Person / Time
Site:	Palo Verde
Issue date:	09/14/1997
From:	Ide W ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
102-04011-WEI-S, 102-4011-WEI-S, NUDOCS 9709230012
Download: ML17312B675 (7)

Text

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SUBJECT:

Provides notification of error discovered in use of acceptable large break LOCA evaluation model which calculate cooling performance of ECCS.Error led to less conservative values of peak cladding temp.

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A001D COPIES RECEIVED:LTR ENCL SIZE-TITLE: OR Submittal: General Distribution CATEGORY 1 REGULAT INFORMATION DISTRIBUTIONSTEM (RIDE) lt ACCESSIGB NBR:9709230012 DOC.DATE: 97/09/14 NOTARIZED: NO FACIL:STN-50-528 Palo Verde Nuclear Station, Unit 1, Arizona Publi STN-50-529 Palo Verde Nuclear Station, Unit 2, Arizona Publi STN-50-530 Palo Verde Nuclear Station, Unit 3, Arizona Publi AUTH.NAME AUTHOR AFFILIATION IDEFW.E.

Arizona Public Service Co. (formerly Arizona Nuclear Power RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

E NOTES:STANDARDIZED PLANT Standardized plant.

Standardized plant.

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05000529 05000530 0 RECIPIENT ID CODE/NAME PD4-2 LA THOMASFK INTERNAL: ACRS NRR/DE/ECGB/A NRR/DRCH/HICB NRR/DSSA/SRXB OGC/HDS2 EXTERNAL: NOAC COPIES LTTR ENCL RECIPIENT ID CODE/NAME PD4-2 PD FILE CENTER 01 NRR DE EMCB NRR/DSSA/SPLB NUDOCS-ABSTRACT NRC PDR COPIES LTTR ENCL D

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10 CFR 50.46 Palo Verde Nuclear Generating Station WilliamE. Ide Vice President Nuclear Engineering TEL 602/3936116 FAX 602/3934077 Mail Station 7605 P.O. Box 62034 Phoenix, AZ65072-2034 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P1-37 Washington, DC 20555-0001 102-04011-WEI/SAB/RMW September 14, 1997

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Units1,2, and 3 Docket Nos. STN 50-528/529/530 Error in Energy Redistribution Factors Used in LOCA/ECCS Performance Evaluation Models, 30 Day 10 CFR 50.46 Report This report is submitted pursuant to 10 CFR 50.46(a)(3)(ii) to provide notification of an error discovered in the use of an acceptable large break loss of coolant accident (LOCA) evaluation model which is employed to calculate cooling performance of PVNGS emergency core cooling systems (ECCS).

The error led to less conservative values of peak cladding temperature (PCT) than should have been calculated in the limiting ECCS analyses of record.

PCT values for plant operations through Cycle 6 corrected for the maximum expected error conform to the required acceptance criterion of 10 CFR 50.46.

Analyses are currently in progress to determine the specific impact of the error on the now completed Cycle 7 for Unit 2 and the current operating cycle, Cycle 7, for Units 1 and On July 11, 1997, Arizona Public Service Company (APS) received Info-bulletin 97-04 from ABB-Combustion Engineering (CE), the fuel vendor'for PVNGS, which described a potential error in the Energy Redistribution Factors (ERF) used in the LOCA analyses.

This bulletin indicated that CE had initiated an evaluation of ERF used in the large and small break LOCA evaluation models.

On August 14, 1997 ABB-CE issued a report to the, Nuclear Regulatory Commission pursuant to 10 CFR 21 regarding this error.

ERF represent the fraction of the total energy generated by the limiting fuel rod which is actually deposited in that rod. The CE evaluation was initiated due to concerns identified

'by APS that the ERF used in the LOCA analyses of record did not properly consider the affects of signiTicant moderator voiding which may occur at various times during the LOCA. The ERF are used in the LOCA analyses to calculate the PCT of the fuel during

( '0 the LOCA. Larger values of ERF will result in higher values of PCT during the LOCA for the same initial value of peak linear heat generation rate (PLHGR).

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U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Error in Energy Redistribution Factors Used in LOCA/ECCS Performance Evaluation Models, 30 DAY 10 CFR 50.46 Report Page 2 Alternatively, the current PCT value will remain unchanged, even with a higher ERF value, provided that the initial PLHGR is reduced.

As a result of the identified error, the energy deposition in the hypothetical hot fuel pin is underpredicted by 0.5 to 1.5%,

depending upon the location of the hot pin within the lattice.

This corresponds to an underestimate of PCT of between 20 and 60 degrees F.

It has been determined that the ERF error applies only to the large break LOCA analysis of record, and does not impact analysis performed for the small break LOCA.

Based on a maximum estimated increase in the PCT of 60 'F, the calculated PCT and PLHGR were evaluated for all fuel cycles of operation for the PVNGS Units.

For fuel Cycles 1 through 6, the calculated PCT with the ERF error would not have exceeded the PCT limit of 2200 'F.

For fuel Cycle 7, the maximum calculated PCT (without including the ERF error) is 2169 'F. Therefore, a 60'F error would result in exceeding 2200 'F. As a result, APS has reduced the allowable PLHGR by 0.2 kw/ft, which makes the calculated PCT, including the ERF error, less than the PCT limit of 2200 'F.

Preliminary plant-specific information received from ABB-CE indicates that the ERF for PVNGS were underpredicted by 0.7%, which would result in a 30 'F change in PCT.

Since these results are preliminary, APS is submitting this report pursuant to the requirements of 10 CFR 50.46(a)(3)(ii), assuming that the maximum error could be 60 'F, which exceeds the 30-day reporting threshold of 50 'F.

APS expects that CE will complete their final plant specific analyses for PVNGS by September 30, 1997.

In the interim, APS has inserted an increased uncertainty penalty factor into the Core Operating Limits Supervisory System (COLSS) for each Unit that will effectively reduce the allowable linear heat rate to ensure compliance with 10 CFR 50.46.

The uncertainty penalty factor was determined using values of PLHGR that were adjusted to reflect the maximum impact of the ERF error, as recommended by ABB-CE. APS has also updated the Core Operating Limits Report (Ref. APS to NRC letter 102-03985-AKK/SAB/RMW,dated July 30, 1997) for each Unit to reflect the impact of this error on the peak linear heat rate limit.

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v U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Error in Energy Redistribution Factors Used in LOCA/ECCS Performance Evaluation Models, 30 DAY 10 CFR 50.46 Report Page 3 Should you have any questions, please contact Scott A. Bauer at (602) 393-5978.

Sincerely, WEI/SAB/RMW/mah cc:

E. W. Merschoff K. E. Perkins K. M. Thomas PVNGS Sr. Resident

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