05000346/LER-1980-025-03, /03X-1:on 800330,control Rod Group 5,rod 11 Absolute Position Indication Declared Inoperable.Caused by Fluctuating Signals Resulting in Numerous Asymmetric Rod Alarms Due to Defective Reed Switch Assemblies

/03X-1:on 800330,control Rod Group 5,rod 11 Absolute Position Indication Declared Inoperable.Caused by Fluctuating Signals Resulting in Numerous Asymmetric Rod Alarms Due to Defective Reed Switch Assemblies

ML19350C225
Person / Time
Site:	Davis Besse
Issue date:	03/24/1981
From:	Werner B TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19350C223	List: 05000346/LER-1980-025, Forwards LER 80-025/03X-1 05000346/LER-1980-025-03, /03X-1:on 800330,control Rod Group 5,rod 11 Absolute Position Indication Declared Inoperable.Caused by Fluctuating Signals Resulting in Numerous Asymmetric Rod Alarms Due to Defective Reed Switch Assemblies
References
LER-80-025-03X, LER-80-25-3X, NUDOCS 8103310623
Download: ML19350C225 (3)

LER-1980-025, /03X-1:on 800330,control Rod Group 5,rod 11 Absolute Position Indication Declared Inoperable.Caused by Fluctuating Signals Resulting in Numerous Asymmetric Rod Alarms Due to Defective Reed Switch Assemblies

Event date:
Report date:
3461980025R03 - NRC Website

text

U. S. tiUCLE AN REGOLAT@CW CO%%ilsFord NRC FORM 3GG (7 77)

LICENSEE EVENT REPORT

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8 63 63 OOCKET NUveER 68 69 EVENT DATE 74 75 REPORT DATE to EVENT DESCRIPTION AND PROSABLE CONSEQUENCES h [TITl I (NP-33-80-35) on 3/30/80 at 0940 hours0.0109 days <br />0.261 hours <br />0.00155 weeks <br />3.5767e-4 months <br />. Control Rod Group 5, Rod 11 absolute position l lo t a l l indication (API) was declared iaoperable due to fluctuating signals which caused num-l [ol4llerous " asymmetric rod" alarms. This placed the unit in the sction state =ent of T.S.

I 10 i s l 1 3.1.3.3.

The rod position was verified at its 100% withdrawn position per the action l [o TTl I statement and the red positten indication was placed in asymmetric-bypass. There was I The rod did I

g l no danger to the health and safety of the public or station personnel.

not vary from its intended position, only the API was faulty.

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34 36 3s 40 43 42 43 to 47 33 CAUSE DESCRIPTION AND CCRRECTIVE ACTIONS h i o lInvestigation has revealed'the apparent cause to be defective API reed switch assem-I to I

lblies. A major' contributing cause of this failure is the excessive temocratures B

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A new "R4C" API system with g lwhich the assemblies and their cables were subjected.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR PCUER STATION UNIT ONE SUPPLEMENTAL INFO?.MATION FOR LER NP-33-80-35 DATE OF EVENT: March 30, 1980 FACILITY: Davis-Besse Unit 1 IDENIIFICATION OF OCCURRENCE:

Fluctuating indication on the absolute position indica-tion (AP1) for Control Rod Group 5-11 Conditions Prior to Occurrence: The unit was in Mode 1, with Power (M'4T) = 305 and Load (Gross L'E) = 0.

Description of Occurrence: On March 30, 1980 at 0940 hours0.0109 days <br />0.261 hours <br />0.00155 weeks <br />3.5767e-4 months <br />, Control Rod Group 5, Rod 11 API was declared inoperable due to fluctuating signals which caused numerous "asy=-

retric rod" alarna. This placed the unit in the action statement of Technical Speci-fication 3.1.3.3 which requires the position of the control cod and its group be prriodically verified and maintained at one of the zone reference positions. The rod position was verified at its 100% withdrawn position per the action statement, and the rod position indfeation was placed in asy=netric bypass.

Designatien of Apparent Cause

• Occurrence: After several months of collecting data on control rod 5-11, the apparent cause has been determined to be defective API reed switch essemblics. A rajor contributing cause to this failure is the excessive temperatures to 1

which the asse blies and tneir cables were subjected. This occurred during several months of operation in which the head assembly cooling fans were not in operation due to d:ficient procedure which s11cwed restart following the 1978 outage without reconnecting cooling fan power cablec. The Reactor Vessel Closure Head Removal and Replacement Pro-c dure, SP 1504.01, was corrected.

Analysis of Occurrence:

There was no danger to the health and safety of the public or to station personnel. The rod did not vary fror its intended position, only the API was f aulty.

Corrective Action

During the last shutdown in March, 1980, a seccion of the position indication (PI) cable was replaced from the top of the PI assembly to the bulk 1: cad for Control Rod Group 5 Rod 11.

This was acco=plished under Maintenance Work Order 80-1930, cnd done as a continuing corrective action for the similar occurrences reported under the previous Licensee Event Reports NP-33-79-141, NP-33-80-07, and NP-33-80-21.

As a result of the investigation, it vaa determined that the reed switch asse=blies of the present "C" style API systen would have to be replaced. A new "R4C" API system was 1

installed under Facility Change Request 79-413.

This systen features built in channel redundancy and new high tenperature API cables.

8 LER #80-025 I

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4 TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE PAGE 2 SUPPLEMENTAL INFORMATION FOR LER NP-33-80-35 Failure Data: There have been previous failures of control rod APIS.

Control Rod Group 5 Rod 11's current symptoms were reported in Licensee Event Reports NP-33-79-141 (79-116), NP-33-80-07 (80-004), and NP-33-80-21(60-015).

LER #80-025 9

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