ML19256G098

LER 79-116/03L-0:on 791123,Control Rod Group 5 Rod 11 Absolute Position Indication Declared Inoperable.Caused by Position Indication Assembly & Cabling Between Electrical Penetration & Rod.Investigation Continues

ML19256G098
Person / Time
Site:	Davis Besse
Issue date:	12/20/1979
From:	Werner J TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19256G093	List: ML19256G092 ML19256G098
References
LER-79-116-03L, LER-79-116-3L, NUDOCS 7912270420
Download: ML19256G098 (3)

Text

' U. S. NUCLE AR REGULATORY COMMISSION NRC FORM OGG (7-77)

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COCKErNUYBER 63 DATE 7 8 60 61 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h o 2 On November 23, 1979 at 2315 hours0.0268 days <br />0.643 hours <br />0.00383 weeks <br />8.808575e-4 months <br />, Control Rod Group 5 Rod 11 Absolute Position IndI-l o13 l cation (API) was declared inoperable due to fluctuating signals which caused numerous I j

o 4 ]" asymmetric rod" alarms. This placed the unit in the action statement of Technical O s l Specification 3.1.3.3. There was no danger to the health and safety of the public or ]

o c to station personnel. The control rod never deviated from its intended position, onlyJ l

"o 7 lthe API was faulty. (NP-33-79-141) l 0 8 80 CAUSE CAUSE CoVP. VALVE SYSTEM SUBCODE SUBCOCE CODE CODE SUeCODE COYPONEN T CODE 7

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h i o lThe exact cause of this occurrence is still undetermined but has been isolated to the l i i l position indication assembly and cabling between the electrical penetration and the g,j,;jrod. Investigation still is in progress at this time. When the plant is started up,  ;

recorder for further j i j 3 l lthe inputs from the test connection will be monitored on a chart

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68 69 1 8 9 419-259-5000, Ext. 231 DVR 79-186 NAME OF PHEPARER John Herner PHONE:

TOLEDO EDISON COMPANY DAVIS-BESSE NUCLE 4R POWER STATION UNIT ONE SUPPLEMENTAL INF0tCIATION FOR LER NP-33-79-141 DATE OF EVENT: November 23, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Fluctuating indication on the absolute position indi-cation f or Control Rod 5-11 ,

i The unit was in Mode 1, with Power (MRT) = 2024, l Conditions Prior to Occurrence: j and Load (Cross MWE) = 685.

t Description of Occurrence: On November 23, 1979 at 2315 hours0.0268 days <br />0.643 hours <br />0.00383 weeks <br />8.808575e-4 months <br />, Control Rod Group 5 Rod 11 Absolute Position Indication (API) was declared inoperable due to fluctuating signals which caused numerous " Asymmetric Rod" alarms. This placed the unit in the action statement of Technical Specification 3.1.3.3 which required the position of the control rod to be verified by actuating one of its zone reference indicators.

The rod position was verified at its 100% withdrawn position per the action state-ment,and the rod was placed in asymmetric bypass.

Designation of Apparent Cause of Occurrence: The exact cause of this occurrence is still undetermined but has been isolated to the position indication assembly and Inves-cabling between the containment external electrical penetration and the rod.

tigation still is in progress at this time.

Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel. The control rod never deviated from its intended position, only the API was faulty.

Corrective Action: The output of Rod 5-ll's API amplifier was put on a trend recorder and noted to fluctuate in an intermittent and irregular manner. Under work request IC-55-24-79, the API input was checked and also found to fluctuate. The position indication (PI) assembly was then disconnected and energized f rom a separate test source, and the output monitored. Fluctuations w 2re again noted, ef fectively isolat-ing the problem to the PI assembly and/or cabling.

During the plant shutdown on December 2,1979, a recorder was placed on the input to Rod 5-ll's API amplifier to observe the voltage change as the PI assembly reed switches operated. No apparent malfunctions were noted. With the assistance of a B&W technical representative, a test connection under Facility Change Request 79-424 was placed between the PI assembly and its associated cabling to monitor the various voltagcs at that point. The PI assembly was also adjusted at the direction of the B&W representa~tive under Maintenance Work Order 79-3691. When the plant is started up the inputs from the test connection will be monitored on a chart recorder for further evaluation.

LER #79-116 fh43 28}

TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE PAGE 2 SUPPLEMENTAL INFORMATION FOR LER NP-33-79-141 Failure Data: There have been sixteen previous failures of control rod APIS, how-ever, the origin of these f ailures has not been due to a common component; see Licensee Event Reports NP-33-77-63, NP-33-78-02, NP-33-78-19, hT-33-78-26, NP-33-78-38, NP-33-78-135, NP-33-78-144, NP-33-78-149, NP-33-79-31, NP-33-79-59, hT-33-79-90, hT-33-7 9-97, NP-33-79-100, NP-33-79-116, NP-33-79-137, and NP-33-79-138.

Rod 5-11 recently had a new PI assembly and hi temperature cable installed.

LER #79-116 1643 286