ML20235X086

Ler:On 870618,in-core Detector Computer Points Inadvertently Removed from Scan.Caused by Personnel Error.Operator Removed Points While Intending to Restore Computer to Normal operation.In-core Detectors Returned to Scan

ML20235X086
Person / Time
Site:	Davis Besse
Issue date:	07/20/1987
From:	Storz L, Stotz J TOLEDO EDISON CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
KA87-0244, KA87-244, LER-LER-870720, NUDOCS 8707240043
Download: ML20235X086 (4)

Text

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APPROVED OMS 8s0. 3150-0104 LICENSEE EVENT DEPORT (LER) **""'""

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• Ass a Davis-Besse Unit 1 0 l510 [0 l 0131416 1 lOFl n l q f tTLE 448 Incore Detectors and Associated Alarm Rendered Inoperable Due to Operator Error.

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EXPECTED YES lif ver. conephew IXDfCTED SUOMISSION DATE] NO l l l AeS,RACT waar u, uoo anc.u . on w.wr os " anremo umr=" sn=1 <w An operator inadvertently removed the incore detector computer points from scan, causing the computer to terminate the periodic updating of the incore detector values. Since the operator did not realize the points were removed from scen, the increased surveillance was not performed as required by Surveillance Requirements 4.2.1 and 4.2.4 The incore detectors were returned to scan approximately 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> after their deletion from scan, restoring the incores to normal operation.

This condition resulted from personnel error. A procedure will be developed and training will be conducted on the sequence to be used when deleting or adding computer points to or from scan and a verification of proper computer restoration. The computer operating procedure will be revised to ensure the necessary precautions are taken to prevent inadvertently deleting essential computer points from scan. Also a software change is being initiated to prevent the incore detectors from being removed from scan from the control room terminal, thereby preventing a recurrence of this event.

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l 0l2 OF 0 l3 j Description of Occurrence:

On June 18, 1987, an operator was restoring the station computer to normal operation following a computer failure. The unit was in Mode 1 with reactor power at 99 percent.

At 2122 hours0.0246 days <br />0.589 hours <br />0.00351 weeks <br />8.07421e-4 months <br /> the operator inadvertently deleted the incore detector computer points from scan. The computer had, as designed, returned those points to scan automatically upon system restoration. With the points deleted from scan, periodic updating of the incore detector values would not occur. The incore detectors were therefore inoperable, as was the associated control room annunciator alarm. Technical Specifications only require incore detector operability when incore detectors are being used to monitor core parameters per ST 5033.01. The surveillance requirement specifies that, in the event the annunciator alarm is inoperable, more frequent surveillance tests must be conducted.

Since the operator did not realize the incore detectors were inoperable, the manual ,

calculations of Axial Power Imbalance and Quadrant Power Tilt were not completed as '

required by Surveillance Requirements 4.2.1 and 4.2.4.

At 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br /> on June 19, 1987 it was discovered during the performance of ST 5033.01, "Incore Detector Channel Check", that the incore detectors were not on scan. The points were immediately returned to scan. This restored the incore detectors to normal operation and removed the requirement for manual calculations per Surveillance Requirements 4.2.1 and 4.2.4.

The inoperability of incare detectors and the associated quadrant power tilt and imbalance alarm neither involved a Limiting Condition for Operation (LCO) nor constituted a violation of Technical Specifications.

Designation of Apparent Cause of Occurrence:

The cause of this occurrence is primarily a personnel error. The operator inadvertently i deleted the incore detectors from scan while intending to restore the computer to normal i operation. The root cause of this occurrence can also be partially determined to be a l design deficiency. The control room computer terminal does not require the capability to l remove the incore detector group from scan. This error was discovered the next day during j the performance of ST 5033.01, resulting in failure to meet the more frequent surveillance j testing required when the annunciator alarm is inoperable. l l

Analysis of Occurrence:

Incore neutron detectors provide o history of power distribution and fuel burnup, which is useful for fuel management purposes. Incore detectors provide no automatic safety functions and are not required to show reactor protection. The Nuclear Instrumentation  !

System (out-of-core detectors), which continuously provides information to the Reactor l Protection System (RPS) to protect the reactor core, remained operable and tilt and  !

imbalance data were automatically calculated and displayed throughout the time period the l l

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This report is submitted to document the inoperability of iricore detectors and their associated annunciator alarm for tilt and imbalance for approximately 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br />. During the time the incores were off scan, data from the out-of-core detectors verified that no core anomalies occurred.

Corrective Action:

A procedure will be developed by September 17, 1987 to include steps for verification of proper computer functioning after returning the computer to operation and training will be corducted on the sequence to be used when deleting or adding computer points to or from scan. The computer operating procedure will be revised to ensure the necessary precautions are taken to prevent inadvertently deleting essential computer points from scan. Also a software change is being initiated to prevent the incore detectors from being removed from scan from the control room terminal, thereby preventing a recurrence of this event.

Failure Data:

This is the first report since a similar situation was noted in 1983. No Licensee Event {

Report was required in that case. Corrective action involved developing the Surveillance l l Test to check the associated alarm. This periodically scheduled Surveillance Test was used to discover this inoperable condition.

l f REPORT NO: NP-33-87-ll PCAQ N0(s): 87-0312 I

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%ms EDISON July 20, 1987 EDISON PLAZA 300 MADISON AVENUE TOLEDO. OHIO 43652-0001 Log No.: KA87-0244 File: (NP-33-87-11)

Docket No. 50-346 License No. NPF-3 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555 Gentlemen:

Davis Besse Nuclear Power Station Unit No. 1 Date of Occurrence June 18, 1987 Enclosed is a Voluntary Report which is being submitted per NUREG 1022 Supplement 1.

Yours truly, l .a O

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Louis F. Storz Plant Manager Davis-Besse Nuclear Power Station LFS/ed l Enclosure cc: Mr. A. Bert Davis -

Regional Administrator I USNRC Region III i 4

i Mr. Paul Byron DB-1 NRC Resident Inspector ,

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