ML20217D028

Part 21 Rept Re Additive Constants Used in MCPR Determination for Siemens ATRIUM-9B Fuel by Core Monitoring Sys Were Found to Be non-conservative.SPC Personnel Notified All Customers w/ATRIUM-9B Lead Test Assemblies

ML20217D028
Person / Time
Site:	Dresden, Quad Cities
Issue date:	04/22/1998
From:	Curet H SIEMENS POWER CORP. (FORMERLY SIEMENS NUCLEAR POWER
To:	NRC
References
REF-PT21-98 34119, NUDOCS 9804240161
Download: ML20217D028 (3)

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GENERAL INFORMATION or OTHER EVENT NUMBER: 34119 LICENSEE: SIEMENS POWER CORP-NUCLEAR DIVISION NOTIFICATION DATE: 04/22/98 CITY: RICHLAND REGION: 4 NOTIFICATION TIME: 12:40 [ET)

COUNTY: BENTON STATE: WA EVENT DATE: 04/21/98 LICENSE #: SNM-1227 AGREEMENT: Y EVENT TIME: 12 : 00 [PDT]

DOCKET: LAST UPDATE DATE: 04/22/98 NOTIFICATIONS ELMO COLLINS, R4 RDO l NRC WOTIFIED BY: DON CURET JIM GAVULA, R3 RDO HQ OPS OFFICER: DICK JOLLIFFE VERN HODGE NRR EMERGENCY CLASS: NOT APPLICABLE 10 CFR SECTION: 1 CCCC 21.21 UNSPECIFIED PARAGRAPH l EVENT TEXT 10CFR PART 21 REPORT - NONCONSERVATIVE PREDICTION OF MONITORED CORE MCPR -

SIEMENS POWER CORPORATION (SPC) PERSONNEL DETERMINED THAT ADDITIVE CONSTANTS USED IN MINIMUM CRITICAL POWER RATIO (MCPR) DETERMINATION FOR SIEMENS ATRIUM-9B FUEL BY THE CORE MONITORING SYSTEM WERE FOUND TO BE l NON-CONSERVATIVE (UP TO 7.6% BASED ON THE ORIGINAL ADDITIVE CONSTANTS).

ALSO SPC PERSONNEL DETERMINED THAT THE UNCERTAINLY IN THE ADDITIVE CONSTANT FOR THIS FUEL DESIGN WAS LARGER THAN PREVIOUSLY ESTIMATED. THE REVISED i UNCERTAINTY HAS THE POTENTIAL TO AFFECT THE MCPR SAFETi LIMIT.

SPC PERSONNEL NOTIFIED ALL SPC CUSTOMERS WITH ATRIUM-9B LEAD TEST ASSEMBLIES OR RELOAD QUANTITIES OF THE FUEL OF THE POSSIBLE NONCONSERVATIVE l PREDICTION OF THE MONITORED MCPR AT CONDITIONS WHERE A SEVERELY UP-SKEWED AXIAL POWER SHAPE COULD OCCUR.

PLANTS AFFECTED ARE DRESDEN UNIT 3 (CYCLE 15), QUAD CITIES UNIT 2

! (CYCLE 15) AND KUOSHENG UNITS 1 & 2.

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EVENT DESCR:PTlON tconanue on separate sheetitnecasanry) l See attached summary of defect related to the non-conservative credictinn nf l

monitored MCPR for core conditions at severe nn-skouma wi=1 -

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Date of report. Defect has been evaluated under Siemens Power cernermeinn Condition Report - CR 6508 dated Febmng 2's.144A.  !

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! Attachment to Siemens Power Corooration - Nuclear Division 10 CFR Part 21 Reoort (Fuel Cvele and Materials Event Notification Worksheet/NRC Form 361 A) of April 21.1998 10 CFR Part 21 Notifcation of Defect Relative to Non-Conservative Predletion of Monitored Core MCPR.

I Additive constants used in MCPR determination for Siemens ATRIUM *-98 fuel by the core monitoring system were found to be non-conservative. Also the uncertainty in the additive constant for this fuel design was determined to be larger than previously ,

estimated. The revised uncertainty has the potential to affect the MCPR safety limit I

However, an interim additive constant uncertainty larger than the value calculated using new CHF data, had been used in safety limit calculations. Because the monitored MCPR could be non-conservative (up to 7.6%) based on the original additive constants, the MCPR safety limit could have been exceeded during the limiting transient while operating with less than 7.6% MCPR margin and with a severely up skewed axial power shape in l

the limiting MCPR assembly.

SPC took immediate steps to determine the potential safety impact on plants operating with ATRIUM-98 fuel and completed an operability assessment on February 26,1998.

The assessment addressed the potentialimpact on both monitored MCPR and the MCPR operating limit. Where necessary, the operability assessment identified conserve ive compensatory actions to ensure that MCPR limits were adequate for ATRIUM-98 fuel. For operation with a positive axial offset (up-skewed power profile), restrictions on the Maximum Fraction of Limiting CPR (MFLCPR) were determined which ensure that adequate MCPR margin exists to cover the potential non-conservatism in ANFB. MFLCPR restrictions of up to 8% were calculated for plants using ATRIUM-98 fuel. For operation when the axial power offset is less than zero (down-skewed power profile), the ANFB correlation is conservative and no limitation on MFLCPR is required.

All SPC customers with ATRIUM-98 lead test assemblies or reload quantities of the fuel were notified of the possible non-conservative prediction of the monitored MCPR at conditions where a severely up-skewed axial power shape could occur.

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