05000346/LER-1981-019-03, /03L-0:on 810323,fluctuating Signals W/Numerous Asymmetric Rod Alarms Received,Resulting in Control Rod 4-7 Absolute Position Indication Inoperability.Probably Caused by Electrical Penetration Module Deficiency

/03L-0:on 810323,fluctuating Signals W/Numerous Asymmetric Rod Alarms Received,Resulting in Control Rod 4-7 Absolute Position Indication Inoperability.Probably Caused by Electrical Penetration Module Deficiency

ML20003G246
Person / Time
Site:	Davis Besse
Issue date:	04/22/1981
From:	Werner J TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20003G245	List: 05000346/LER-1981-019, Forwards LER 81-019/03L-0 05000346/LER-1981-019-03, /03L-0:on 810323,fluctuating Signals W/Numerous Asymmetric Rod Alarms Received,Resulting in Control Rod 4-7 Absolute Position Indication Inoperability.Probably Caused by Electrical Penetration Module Deficiency
References
LER-81-019-03L, LER-81-19-3L, NUDOCS 8104280533
Download: ML20003G246 (3)

LER-1981-019, /03L-0:on 810323,fluctuating Signals W/Numerous Asymmetric Rod Alarms Received,Resulting in Control Rod 4-7 Absolute Position Indication Inoperability.Probably Caused by Electrical Penetration Module Deficiency

Event date:
Report date:
3461981019R03 - NRC Website

text

U. S. NUCLE AR C EGULATCRY COMMISSION NRC FORM 366 LICENSEE EVENT REPORT CONTROL BLOCK: l l

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60 61 DOCKET NUMBEH 68 69 EV ENT D ATE 74 75 REPORT DATE 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h 1

Q l (NP-33-81-21) On 3/23/81 at 0525 hours0.00608 days <br />0.146 hours <br />8.680556e-4 weeks <br />1.997625e-4 months <br />, Control Rod 4-7 Absolute Position Indication l (API) was declared inoperable due to fluctuating signals with numerous "asyc: metric l

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[ rod" alarms. This placed the unit in the action statement of Technical Specification l o 4 lTTTI i 3.1.3.3.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-81-21 DATE OF EVENT: March 23, 1981 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Control Rod 4-7 Absolute Position Indication (API)

Fluctuations Conditions Prior to Occurrence: The unit was in Mode 1 with Power (NWT) = 2495 and Load (Gross MRE) = 843 Description of Occurrence: On March 23, 1981 at about 0525 hours0.00608 days <br />0.146 hours <br />8.680556e-4 weeks <br />1.997625e-4 months <br />, Control Rod 4-7 API was declared inoperable due to fluctuating signals with numerous " asymmetric rod" alarms. This placed the unit in the action statement of Technical Specifica-tion 3.1.3.3 which required the position of the control rod to be verified by actuat-ing one of its zone reference indicators. The rod position was verified at its 100%

withdrawn position, and the rod position indication was placed in asymmetric bypass.

Designation of Apparent Cause of Occurrence: The exact cause of this occurrence is undetermined. The problem has been isolated to the API signal between the +5VDC into containment at the outer containment electrical penetration terminal board and the return API signals at the same location. During the 1980 refueling, Facility Change Request 79-413 changed the position indication (PI) assemblies and PI cables on the reactor head. Because of this and information from previous troubleshooting of similar API problems, it appears the API signal leads are picking up interference in the electrical penetration module.

Analysis of Occurrence: There tas no danger to the health and safety of the public or to station personnel. The red did not vary from its intended position, only the API was faulty.

Corrective Action

Work Request IC-55-10-81 was written to place a brush recorder on the signal leads at the outer containment electrical penetration terminal board.

Because of information gathered at this point and information gathered from other rods with similar problems (see Licensee Event Reports NP-33-79-141 (79-116),

NP-33-80-07 (80-004), NP-33-80-21 (80-015), NP-33-80-35 (80-80-025), and NP-33-81-11 (81-012) ), it was felt that interference was being introduced within the electrical penetration. Facility Change Request 79-401 has been written to obtain spare pene-tration modules for use in replacing defective modules. Until this facility change request has obtained final approval and spare modules are purchased, Facility Change Request 81-080 brought Rod 4-7s API signals through installed spare wires in its pre-sent penetration.

LER #81-019

b TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE S'PPLEMENTAL INFORMATION FOR LER NP-33-81-21 PAGE 2 Failure Data: There were numerous previous failures of control rod APIS prior to the 1980 refueling outage and implementation of Facility Change Request 79-413.

There has been one API failure since the outage, see Licensee Event Report NP-33-81-11 (81-012).

LER #81-019 O

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