ML19320A100

AO 50-313/74-13:on 741123,reactor Protection Sys Failed to See Coolant Pump Trips.Caused by Under/Overpower Monitoring Relay Maladjustment.Relays Bench Tested & Overpower Circuit Holding Coils Removed

ML19320A100
Person / Time
Site:	Arkansas Nuclear
Issue date:	12/03/1974
From:	Cavanaugh W, Pettit A, Reuter D ARKANSAS POWER & LIGHT CO.
To:
Shared Package
ML19320A095	List: ML19320A094 ML19320A100 ML19320A104 ML19320A110
References
NUDOCS 8004140706
Download: ML19320A100 (3)

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i. Abnormal Occurrence Report No.

50-313/74-13

2. Report Date: 12/ 3/74 3. Occurrence Date: 11/23/74

4. Facility: Arkansas Nuclear One-Unit 'l Russellville, Arkansas

. S. Identification of Occurrence:

Reactor Protection System failure to see keactor Coolant Pump trips due to underpower/ overpower monitoring relay maladjustment.

6. Conditions Prior to Occurrence:

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Steady-State Power Reactor Power , c;t 1. 7 MWth Ilot Standby Net. Output 210 MWe Cold Shutdown Percenttof Full Power 20 %

, Refueling Shutdown I

.} Routine Startup Operation

. Routine Shutdown V Operation -

Load Changes During Routine Power Operation t

Other (Specify) X

'l Power Transient testing per TP800.01, " Power Escalation Sequence" Test.

7. Description of Occurrence: '

At 2202, Reactor Coolant Pumps A *and D were shutdown for two pump testing .

dureTP800.23, per TP300.01. " Unit Load Transieint Test", called for by controlling proce-seen. A check of the RPS revealed that the pump trips were not RC Pumps A and D were restarted and B and C were tripped. The RPS ~;

again gave no indication that the two pumps had tripped.

At 0235 on 11/25/74, Reactor Power at 25%, Reactor Coolant Pump D was tripped for 3 pump operation test. The pump monitor relay providing -

indication of pump trip to the RPS did not drop out. D Pump was restarted and again again tripped with similar results. A Pump was tripped and D Pump was restarted. -

'Ihe pump monitor relay on A Pump responded properly.

Concurrent with C Pump trip, the D Pump monitor relay also tripped (D Pump still running) resulting in a reactor trip.

8 0 0 414 0 70/f i

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Abnormal Occurrence Report No. 50-313/74-13 Sheet 2

8. Designation of Apparent Cause of Occurrence:

Design X Procedure Manufacture Unusual Service Condition Including Installation / Environmental Construction Component Failure Operator Other (Specify) .

. The holding coil of this type of relay is norpally used to hold the contact arm in the tripped position after an overpower or underpower situation. In this application, the relay had to be adjusted so that the contact arm could overcome the electromagnetic force at a pre-determined power. On 11/22/74, a relay technician adjusted the holding coils as they were designed to be ad J usted, resulting in a less than conservative setting of the power monitoring relays.

\s _,/ 9. Analysis of Occurrence: -

The relays were immediately readjusted and tested by tripping each pump and verifying the RPS response. There were no safety implications or hazards to the public health or safety due to the immediate corrective action.

10. Corrective Action:

The underpower monitoring relays were removed during th< following plant ^

shutdown and bench tested. The overpower circuit holding coil of each relay was removed, enabling a more accurate setting of the relays and a more reliable operation. A test feature was added to each relay circuit to ensure the operability of each relay, allowing testing on a scheduled -

basis.

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'Y l Abnormal' Occurrence Report No. 50-313/74-13 i Sheet 3 i

11. Failure Data: '

The overpower /underpower relays can be identified by:

General Electric .

Model #: 12CFW IIE24A -

Type: CFW j Rangei 0-800 Watts d

12. Reviews and-Approvals:

Reviewed and Approved by: Plant Safety Committee Yes (X) No ( )

Plant Superintender.t Yes (X) No ( )

Re JWA 704 Date: 11/29/74 d - h . ference:e -

Reviewed by:

'M MM // . MM Licensing Supervisor Date: / 2# /2./7 6/

Approved by: /* /' . '97)((g[,-7/f/ Date: / >4/7 V Saf Committee Approved by: /, _ U , /'

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/ Manager of NucIcar 6rvic'es Date: /2-

[74 Approved by:(0/;w f. // reg!w'.a/,/4pQ. sylLZ Date: /2/1/7 f

/ Director of Power Pr6ducti'on Approved by: [M Date: 4M3/M '

Senior Vice President

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