ML19257A166

LER 79-120/03L-0:on 791129,numerous Asymmetric Alarms & Faults Received from Control Rod Group 7,rod 5.Caused by Failure of Reed Switch in Position Indication Assembly. Assembly Replaced & Adjusted

ML19257A166
Person / Time
Site:	Davis Besse
Issue date:	12/26/1979
From:	Werner J TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19257A162	List: ML19257A161 ML19257A166
References
LER-79-120-03L, LER-79-120-3L, NUDOCS 8001020379
Download: ML19257A166 (2)

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NRC FORM 3G6

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LICENSEE EVENT REPORT

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l 1 lJO1 hl 57 LAT 68 14 15 LICENSE NUMBEH 26 7 8 9 LICENSEE CODE CON'T

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7 8 60 61 COCKET NUVB ER EVENT DESCRIPTION AND PROB A8LE CONSEQUENCES h o 2 l On 11/29/79 operations personnel received numerous asymmetric alarms and faults from i l Control Rod Group 7, Rod 5 (Rod 7-5). As the rod position could not be verified by l o 3 l

o 4 l actuating any of its zone ref erence indication limit switches, reactor power was re-o s duced and the reactor protection system "hi flux" trip bistables were reset in compli-j There was no danger to the health j o e l ance with the action statement of T.S. 3.1.3.3.

o 7 l and safety of the public or station personnel. The control rod never deviated from l l

o e I its intended position. (NP-33-79-137)

CAUSE CAUSE COYP. VALVE SYSTENT SUBCODE CODE SUBCODE COMPONENT CODE SUBCODE CODE o 9 lR lB @ l El@ l Al@ l1l N l S l T l R l U j@

12 13 18 19 El@ lZl@ 20 7 8 9 10 11 REVISION SEQUENTI AL OCCURRENCE REPORT

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EVENT YEAR s; I 71 91 1-1 23 1112101 24 26 l/l 27 I of 31 28 M

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l33Algl34C lg l36Z lg 31 40 41 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h

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i o l The cause of this occurrence is attributed to the f ailure of a reed switch in the posi-l 1i li j tion indication assembly. This failure is apparently not due to an oxide buildup on l 3,;7; l the switch contacts as were previous, failures. On December 2,1979, the position 1 3 l indication assembly for Rod 7-5 was replaced and adjusted.

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• .POWER oTHER STATUS Dis OV RY DISCOVERY DESCRIPTION STA 'S fitsl U@ l 014 l 4l@l NA l l A lgl Operator observation l ACT?VITY CONTENT AMOUNT OF ACTIVITY LOCATION OF RELEASE 1 6 IZl REtEASE@D OF RELEASE l Zl@l NA l NA 80 44 45 7 8 9 to 11 PERSONNEL EXPOSURES NUVBER TYPE DESCRIPTION na

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• l',5U E D DESCRIPTION L2_L.J LN_jhl NA l llIIIIlIl lIII 68 69 60 ;

7 8 9 to DVR 79-181 John Werner PHONE: 419-259-5000. Ext. 231 NAME OF PREPARER

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d TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-137 DATE OF EVENT: Novenber 29, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Control Rod Drive 7-5 Absolute Position Indication (API) Failure Conditions Prior to Occurrence: The unit was in Mode 1, in three reactor coolant pump operation, with Power (MWT) = 1220, and Load (Gross MRE) = 411. Description of Occurrence: On November 29, 1979 operations personnel received numer-ous asymmetric alarms and faults from Control Rod Group 7, Rod 5 (Rod 7-5) while con-trolling on Group 7. Rod 7-5 API was declared inoperable at 0640 hours, placing the unit in the Action Statement of Technical Specification 3.1.3.3. The Action Statement required the rod position to be verified by actuating one of its zone reference indi-cators or to reduce thermal power to I:60% of the allowable power, and to reset the hi flux trip bistable setpoint to 6 70% of the allowable power. Since the rod posi-tion could not be verified by actuating any of its zone reference indication limit switches, reactor power was reduced to approximately 46% of full power, and the reac-tor protection system "hi flux" trip bistables were reset to approximately 54% of the full power. Designation of Apparent Cause of Occurrence: The cause of this occurrence is attri-butable to the failure of a reed switch in the position indication assembly. This failure is apparently not due to an oxide buildup on the contacts as the application of a high voltage to break down the oxide level had been unsuccessfully attempted.

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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, and reactor power was reduced as required. Only the absolute position indication was faulty. Corrective Action: During the reactor shutdown on December 2,1979, as Rod 7-5 was decreasing under 30% withdrawn, the API first f ailed to zero and then returned to the group average. This indicated a faulty reed switch. On December 2,1979, the PI assembly for Rod 7-5 was replaced and adjusted per Maintenance Work Order 79-3693. Failure Data: There have been previous failures of control rod APIS, however, the origin of these f ailures does not appear to be all due to a common component failure; see Licensee Event Reports NP-33-77-63, NP-33-78-02, NP-33-78-19, NP-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, NP-33-79-90, NP-33-79-97, NP-33-79-100, and NP-33-79-116. LER #79-120 I6b3 ff9}}