05000327/LER-1981-089-03, /03L-0:on 810719,operator Observed Rod Position Indication for Shutdown Rods G13 & B12 Indicated Full Insertion Although Rods Were Withdrawn.No Dropped Rod Alarm Received.Caused by Power Supply Failure Due to Short

/03L-0:on 810719,operator Observed Rod Position Indication for Shutdown Rods G13 & B12 Indicated Full Insertion Although Rods Were Withdrawn.No Dropped Rod Alarm Received.Caused by Power Supply Failure Due to Short

ML20010C559
Person / Time
Site:	Sequoyah
Issue date:	08/12/1981
From:	Harding M, Wilkey A TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20010C557	List: 05000327/LER-1981-089, Forwards LER 81-089/03L-0 05000327/LER-1981-089-03, /03L-0:on 810719,operator Observed Rod Position Indication for Shutdown Rods G13 & B12 Indicated Full Insertion Although Rods Were Withdrawn.No Dropped Rod Alarm Received.Caused by Power Supply Failure Due to Short
References
LER-81-089-03L, LER-81-89-3L, NUDOCS 8108200189
Download: ML20010C559 (2)

LER-1981-089, /03L-0:on 810719,operator Observed Rod Position Indication for Shutdown Rods G13 & B12 Indicated Full Insertion Although Rods Were Withdrawn.No Dropped Rod Alarm Received.Caused by Power Supply Failure Due to Short

Event date:
Report date:
3271981089R03 - NRC Website

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i l-i2l l At 1016(c) on 7/21/81 with Unit 1 in Mode 3 (544 F & 2235 psig), the'Un' t Operator I observed that rod positi6n in'dication for shutdown rods G13 and B12 indicated fully o a lt i4l l inserted although the rods had been fully withdrawn. The operator verified the absence,

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[olsl l of a dropped rod aiarm, then tripped the shutdown banks to comply with the action lo is ] l statement of LCO 3.1.3.3..

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r enn~ ~ee V.llity Auth;rity Sequoyah Nuclear Plant LER SUPPLEMENTAL INFORMATION SQRO-50-327/81089 At 1016 CDT on 7/21/81 with Unit 1 in Mode 3 (544 F & 2235 psig), the Unit Operator observed that rod position indication for shutdown rods G13 and B13 indicated that they were fully inserted although the rods had been fully withdrawn. After verifying that no dropped rod alarm had been received, the operator tripped the shutdown banks to comply with the action statement of LCO 3.1.3.3.

During maintenance on a signal conditioning module in the system, an extender board had been positioned at an angle which caused the +13VDC supply to short to ground. This resulted in the loss of regulation on the +26VDC main supply as well as the loss of the t13VDC alternate supply, When the indicators fell to zero due to the associated operational ampli-fiers being supplied by the +13VDC, the fault was diagnosed and the system was declared inoperable and the power supply fuses were pulled to prevent further damage to the equipment.

Subsequent investiga+ 'on determined that an alignment spacer normally installed in one pin of the module connector had been pulled out when the module had been removed. In addition, the module's side guides were also discovered to be loose. These two factors contribu'.ed to the electtical short which caused the event.

The signal conditioning module's side guides were tightened to prevent a recurrence of the short, the main and auxiliary power supplies were replaced, and the rod position indication system was declared operable at 1838 CDI.