ML20024A362

LER 83-024/03L-0:on 830511,while Starting Up from 830510 Reactor Trip,Quadrant Power Tilt in Quadrant Yz Exceeded Tech Spec steady-state Limit.Caused by Inherent Design of B&W NSSS & Negative Moderator Temp coefficient.W/830609 Ltr

ML20024A362
Person / Time
Site:	Davis Besse
Issue date:	06/09/1983
From:	Murray T, Oconnor B TOLEDO EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
K83-855, LER-83-024-03L, LER-83-24-3L, NUDOCS 8306170142
Download: ML20024A362 (4)

Text

NRC FORM 366 U. S. NUCLEAR REGULATORY COMMISSION (7-77) .

'. ' - LICENSEE EVENT REPORT CONTROL BLOCK: l l l l l l l (PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION) 1 6 j o l t l l 0lH l D l B l S l 1l@l 0 l 0 l -l 0 l 0 l 0 l 0 l 0 l - l 0 l 0 l@l 4 l 1 l 1 l 1 l 1 l@l l l@

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REPORT DATE 80 EVENT DESCRIPTION AND PROBA8LE CONSEQUENCES h l a l a l l (NP-33-83-31) on 5/11/83 while the unit was in the process of starting up from a reac-i lol3l l tor trip on 5/10/83, the quadrant power tilt (QPT) "in the "YZ" quadrant reached 3.06, l I o l a i l which exceeds the steady state tilt limit (3.03) of Tech Spse 3.2.4 There was no  !

l o I s ! l danger to the health and safety of the public gr station personnel. The QPT was far l I o Is l Ibelow the transient limit of 8.53 and the maximum tile limit of 20.0. l l o 171 1 .

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS i)40 h g g ,

l i l o l ] The cause is the inherent desig'n of the B&W Nuclear ljteam Supp'ly S;istem _ coupled with al

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li j i l llarge negative moderator temperature coefficient (MTd)'a,t the end of corr'11fe.-.,Dur-I

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g,,7; l ing startup, the OTSG 1-2 lifted off low level limits ahead 9 f OTSG 1-1 allowing the 1 1

l g l cold leg temperature in loop 2 to decrease slightly. The large negative MTC c3used: l l g l power to increase in the "YZ" quadrants. QPT was within stead,y state limits in'36 miqutes.

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TOLEDO

%ms EDISON June 9, 1983 Log No. K83-855 File: RR2 (NP-33-83-31)

Docket No. 50-346 License No. NPF-3 Mr. James G. Keppler Regional Administrator, Region Ill Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137

Dear Mr. Keppler:

LER No.83-024 Davis-Besse Nuclear Power Station Unit 1 Date of Occurrence: May 11, 1983 Enclosed are three copies of Licensee Event Report 83-024 which are being submitted in accordance with Technical Specification 6.9 to provide 30 day

-written notification'of the subject occurrence.

Yours truly,

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t'* Terry'D. Murray i '\ '

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-i Mr. Norman Haller, Director s

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• Office of Management and Prograa Analysis Fncl: 3 copies "'- '

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DATE OF EVENT: May 11, 1983 r ,

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FACILITY: Davis-Bess'e Unit 1 ~

IDENTIFICATION.0F CCCURRENCE: The steady state quadrant power tilt limit was exceeded '

4 Coaditions Prior to Occurrence: .The unit was in Mode 1, with Power (MWT)

= 690 and Load (Gross MWE) = 230.

, bescription of Occurreice: The unit wa3 in tne process of starting up

,from a reactor trip which occurred on May 10, 1983'at 1027 hours0.0119 days <br />0.285 hours <br />0.0017 weeks <br />3.907735e-4 months <br />. The 1

fperators were increasing' reactor power to lif t the once through steam

- . generator (OTSG) water level off low level limit control at 35 inches. At 0119 hours0.00138 days <br />0.0331 hours <br />1.967593e-4 weeks <br />4.52795e-5 months <br />, with the unit increasing <from 25% power, the operators received an annunciator alarm " Tilt, Imbalance, Rod Insertion Limit". The Nuclear Steam Supply Summary on the computer.showed a quadrant power tilt of 3.06 in the "YZ" quadrant. The steady state tilt limit of 3.03 per Technical ,

Specification 3.2.4 was exceeded. The operators slowly increased power to get both OTSGs off low level limit control ind thereby balance feedwater flows. The steady state quadrant power'tiltlwas reduced to less than the steady state limit in 36 minutes, which complies with the Technical i Specification action of 3.2.4 to restore thei tilt to within limits within two hours.  ; ,

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Designation of Apparent Cause of Occurrence: The cause of this occurrence is the inherent design of the B&W Nuclear Steam Supply System coupled with '

the large negative moderator temperature coefficient at the end of core life. During a startup, the OTSG level is held at 35 inches up to approxi-mately 25% power to allow Tavg to ramp from 532' to 582'. As power is increased fiom 25%, however, the Integrated Control System (ICS) holds Tavg constant and raises OTSG' level. During this startup, the OTSG 1-2 lifted off of low level limits slightly ahead of OTSG 1-1 allowing cold leg temperature .in loop 2 to slightly decrease. The large negative moderator tempivature coefficient caused power to increase in the YZ and ZW quadrants. As power was increased a few percent, however, the OTSG 1-1 lifted off low level limit control thereby balancing the feedwater flows and the quadrant pcwer tilt returned to normal.

Analysis of Occurrence: There was no danger to the health and safety of the public or station personnel. The quadrant power tilt of 3.06 exceeded the steady state limit by only 0.03 and was far below the transient limit of 8.53 and the maximum tilt limit of 20.0. The plant operators took the correct course of action to raise reactor power balancing the feedwater flows which in turn equalized the loop cold leg temperatures reducing the tilt to within limits.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE

, SUPPLEMENTAL INFORMATION.FOR LER NP-33-83-31 PAGE 2 4

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Corrective Action: No definite additional corrective actions are required.

iTEe operators are well aware of the necessity to monitor feedwater flows

'. to each OTSG, ;In addition to this, the ICS will perform this function

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, automatically ,by the ATc controller once both OTSGs are off low level s limit control'. The only time a minor upset occurs during a startup is at j the instaat the first CTSG lifts off of low level limit control. The 3 correct iction is to raise power and ensure the other OTSG 1evel also increases. This' action was properly performed by the reactor operators,

/ therefore, ac corrective action is required.

d Failuce;Datai Although there have been previous occurrences during which quadrant power. tilt exceeded the steady state limit of Technical Specifica-tion 3.2.4,.-none have occurred due to the inherent design of the B&W

j. Nuclear Steam. Supply System coupled with the large negative moderator temperature coefficient at the end of core life. Reference Licensee Event Reports NP-33-81-55 (81-047) and NP-33-83-61 (83-052) for a description of these occur.rences. 5 LER #83-024'f ,

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