05000285/LER-1980-026-03, /03L-0:on 801030,AB-1 Matrix Relay Failed to Trip Clutch Power Supplies.Caused by Failure of Matrix Circuit to Break Contact.Relay Replaced & Applicable Surveillance Test Performed to Demonstrate Operability

/03L-0:on 801030,AB-1 Matrix Relay Failed to Trip Clutch Power Supplies.Caused by Failure of Matrix Circuit to Break Contact.Relay Replaced & Applicable Surveillance Test Performed to Demonstrate Operability

ML19340B863
Person / Time
Site:	Fort Calhoun
Issue date:	10/30/1980
From:	Core M OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19340B861	List: 05000285/LER-1980-026, Forwards LER 80-026/03L-0 05000285/LER-1980-026-03, /03L-0:on 801030,AB-1 Matrix Relay Failed to Trip Clutch Power Supplies.Caused by Failure of Matrix Circuit to Break Contact.Relay Replaced & Applicable Surveillance Test Performed to Demonstrate Operability
References
LER-80-026-03L, LER-80-26-3L, NUDOCS 8011120476
Download: ML19340B863 (4)

LER-1980-026, /03L-0:on 801030,AB-1 Matrix Relay Failed to Trip Clutch Power Supplies.Caused by Failure of Matrix Circuit to Break Contact.Relay Replaced & Applicable Surveillance Test Performed to Demonstrate Operability

Event date:
Report date:
2851980026R03 - NRC Website

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?S NEPCAT DATE 30 EVENT DESCRIPTION ANO PACBABLE ccNSECUENC55 10 21 l During testing of the matrix logic for the reactor protective system, it was dis-I The m j covered that the AB-1 matrix relay failed to trip the clutch power supplies.

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LER fio.80-026 Omaha Public Pcwer District Fort Calhoun Station Unit tio.1 Docket flo. 05000285 Attachment flo. 1 l

Safety Analysis

The RPS uses a two-aut-of-four logic trip system. To automatically initiate ~ a reactor trip, two trip units in two of the four channels, must be in a tripped condition.

If two trip units are tripped, the matrix logic system will interrupt pcwer to the CEDM clutch assemblies, thereby dropping the control rods into the core.

The AB-1 relay is used as part of a matrix ladder consisting of a set of twenty four contacts. There are six matrix ladders employed in the RPS which provide the required ccmbinations of two-out-of-four trip logic (i.e. A/S, A/C, A/0, B/C, B/D, C/D).

If any set of contacts in the AB matrix ledder opens, relay AB-1, 2, 3 and 4 de-energi:e, opening redundant contacts to the four M relays which supply power to PS 1, 2, 3 and 4, the clutch power supplies.

Opening tne contacts from relays AB-1 o_r_ AB-2 will interrupt pcwer to PS-1 and ?S-3.

Likewise, coening con-tacts from relays AB-3_o_r_ AB-4 will interrupt power to PS-2 and PS-4.

Since'the AB-2 relay, the redundant relay to AB-1 was fully Opera-tional at the time of failure of the AB-1 relay, the AB matrix was operaticnal and would have performed the required function, that is, to trip the clutch power supplies.

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LER No.80-026 Omaha Public Power District Fort Calhoun Station Unit No.1 i

Docket No. 05000285 i

Attachment No. 2

Corrective Action

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The AB-1 matrix relay was removed and replaced with a new relay as required by I.E.Bulletin 80-19.

The matrix was then retested by per-ferming the applicable surveillance test, ST-RPS-ll.

The licensee has ordered a new style relay that will have dry con-tacts and will install the new relays during the 1981 Refueling Outage.

The licensee will continue to perform the increased surveillance as re-quired by I.E.Bulletin 80-19.

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e LER No.80-025 Omaha Public Power District Fort Calhoun Station Unit No.1 Docket No. 05000285 Attachment No. 3 Failure Data This is the fourth reportable occurrance of its kind at Fort Calhoun Station Unit No.1.

See LER's80-008, 79-009 and 79-012.

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