05000346/LER-1979-100-03, /03L-0:on 791014,group 7,rod 7 Absolute Position Indication Showed Asymmetric W/O Clearing.Caused by Power Supply Cable.Cable Replaced W/High Temp Cable.Rebuilt Position Indicator Tube Installed

/03L-0:on 791014,group 7,rod 7 Absolute Position Indication Showed Asymmetric W/O Clearing.Caused by Power Supply Cable.Cable Replaced W/High Temp Cable.Rebuilt Position Indicator Tube Installed

ML19256E989
Person / Time
Site:	Davis Besse
Issue date:	11/09/1979
From:	Naylor R TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19256E988	List: 05000346/LER-1979-100, Forwards LER 79-100/03L-0 05000346/LER-1979-100-03, /03L-0:on 791014,group 7,rod 7 Absolute Position Indication Showed Asymmetric W/O Clearing.Caused by Power Supply Cable.Cable Replaced W/High Temp Cable.Rebuilt Position Indicator Tube Installed
References
LER-79-100-03L, LER-79-100-3L, NUDOCS 7911160398
Download: ML19256E989 (2)

LER-1979-100, /03L-0:on 791014,group 7,rod 7 Absolute Position Indication Showed Asymmetric W/O Clearing.Caused by Power Supply Cable.Cable Replaced W/High Temp Cable.Rebuilt Position Indicator Tube Installed

Event date:
Report date:
3461979100R03 - NRC Website

text

NRC FORM 36G (7 77)

LICENSEE EVENT REPORT CONTROL BLOCK: l l

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8 60 61 DOCKET NUUUER t,d bJ EVENT DATE 14 75 REPORT D ATE 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h o 2 l On October 14, 1979 at 1638 hours0.019 days <br />0.455 hours <br />0.00271 weeks <br />6.23259e-4 months <br />, croup 7 rod 7 Absolute Position Indication (API) l

_ l o l 3 l l indicated asymmetric for a period of two minutes, cleared, and again indicated asym-l metric for a period of four minutes and did not clear.

This placed the unit in the l

o 4 l Action Statement of Technical Specification 3.1.3.3.

Unit power was reduced to 60%

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_ l 016 I l and the high_ flux _setpo_ int _r_gduced to 70L There was no danger to the health and o 7 I safety of the public or stalion_ personnel. The Relative Position Indicators and i

j o is l l zcue reference indication were operable.

(NP-33-79-116) l SYSTEM

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[ li l o l l The problem appears to be in the cable which supplies power to the API and returns the[

l signal to the position indication panels. Under Maintenance Work Order 79-3229, the !

i i cable was replaced with a new high temperature cable and a rebuilt PI tube was instal-1

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Investigation of recurring API problems continues.

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.DVR 79-150 NAME OF PREPARER PHONE:

4 TOLEDO EDISON COM ANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-116 DATE OF EVENT: October 14, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Group 7 Rod 7 Absolute Position Indication inoperable due to repeated asy= metric alarms Conditions Prior to Occurrence:

The unit was in Mode 1, with Power (MWT) = 2772, and Load (Gross rie) = 923.

Description of Occurrence: On October 14, 1979 at 1638 hours0.019 days <br />0.455 hours <br />0.00271 weeks <br />6.23259e-4 months <br />, Group 7 Rod 7 Absolute Position Indication (API) indicated asymmetric for a period of two minutes, cleared, The and again indicated asy= metric for a period of four minutes and did not clear.

API for Rod 7 of Group 7 was declared inoperable. This placed the unit in the Action Statement of Technical Specification 3.1.3.3 which recuires all regulating control rod API and relative position indications (RPI) be operable and capable of determining

- the control rod positions within + 6.5% in Mode 1.

The unit power was reduced to 60% and the high flux setpoint was reduced to 70%. The RPI and zone reference indication were operable while the API was inoperable.

Designation of Apparent Cause of Occurrence: The apparent cause of the occurrence appears to be in the cable which supplies power to the API and returns the signal to the position indication panels. During a previous shutdown, the position indicator tube for Rod 7-7 was replaced and the old tube sent to Diamond Power, the PI tube vendor. Their investigation of the tubes sent back was that the PI tubes had exper-ienced a high temperature condition above its rating. This probably occurred when the ventilation f ans for the head were not operating at an earlier date.

Analysis of Occurrence: There was no danger to the health and safety of the public or station personnel. The relative position indication and zone reference indication for the rod was operating and the group position indicator was indicating properly while the API channel was inoperable.

Corrective Action

Under Maintenance Work Order (MWO) 79-3229, the cable from the bulkhead to the reactor head was changed for Rod 7-7 with a new high temperature cable, and a partially rebuilt PI tube was installed.

Since the unit has returned to power, the API has been operable. The station and Babcock and Wilcox are investigating several permanent corrective actions for the replacement of cables and PI tubes.

Procedure modifications to SP 1105.09 have been incorporated to assure that service structure ventilation f ans are in service during final walkdown.

Failure Data: Previous API failures were reported in Licensee Event Reports NP-33-77-63, UP-33-78-144, NP-33-78-149, NP-33-79-31, NP-33-79-90, NP-33-79-97, and NP-33-79-100.

1341 347 LER #79-100