05000298/LER-1992-001, :on 920111,both Pumps Exceeded Setpoints of High Flow Isolation Switch.Caused by Insufficient Throttling of Valve.Group 3 Isolation Was Reset & B Pump Placed Into Operation

:on 920111,both Pumps Exceeded Setpoints of High Flow Isolation Switch.Caused by Insufficient Throttling of Valve.Group 3 Isolation Was Reset & B Pump Placed Into Operation

ML20092D729
Person / Time
Site:	Cooper
Issue date:	02/10/1992
From:	Meachum J, Myers J NEBRASKA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CNSS923542, LER-92-001, LER-92-1, NUDOCS 9202140209
Download: ML20092D729 (4)

LER-1992-001, on 920111,both Pumps Exceeded Setpoints of High Flow Isolation Switch.Caused by Insufficient Throttling of Valve.Group 3 Isolation Was Reset & B Pump Placed Into Operation

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation
2981992001R00 - NRC Website

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Nebraska Public Power District CNSS923542 February.'10, 1992 U.S. Nuclear Regulatory Commission Document Control Desk-l; Washington, D.C.

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Dear Sir:

Cooper Nuclear Station-Licensee Event Report 92 001, Revision 0, is being forwarded as an attachment to this letter, Sincerely, e

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,v,..,u.m.., n e i on January 11, 1992, with the plant in normal power operation, the B Reactor Water Clean Up (RWCU) pump was started to transfer operation from the A to the B RWCU i

pump.

Shortly after starting the pump, the licensed operatar observed the RWCU high flow alarm, and then the closure of the RWCU Primary Containment isolation valves and actuation of the Primary Containment Group 3 indication lights. The RWCU Filter /Demineralizers had been previously removed from service, and the bypass valve,_RWCU MOV H074, was throttled to maintain normal pump discharge pressure.

The isolation resulted from insufficient throttling of the RWCU MOV M074 valve.

This allowed the combined flow from both pumps to exceed the setpoint of the high flow isolation switch. With the Filter /Demineralizers isolated, system flow indication is not available in the Control Room. The system operating procedure will be revised to direct the use of local flow indications when shifting pumps with the Filter /Demineralizers isolated.

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A.

Event Descrintion On January 11, 1992, with the plant in normal power operation, the B 4

Reactor Water Clean Up (RWCU) pump was started to transfer operation from the A to the B RWCU pump to perform post maintenanco testin5 of the i

B pump.

Shortly after starting the pump, the licensed operator observed the RWCU high flow alarm, and then the closure of the Primary Containment RWCU isolation valves and actuation of the Primary l

Containment Group 3 indication lights. The RWCU Filter /Demineralizers i

had been previously removed from service, and the bypass valve, RWCU MOV.M074, was throttled to maintain normal pump discharge pressure.

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Plant itAtua.

The plant was in normal power operation at approximately 100 percent power, with the Reactor at 1000 psig.

The RWCU Filter /Demineralizers were removed from service, and the bypass valve, RWCU MOV M074 throttled open.

The A RWCU pump was in operation.

C.

Basis for Renort I

Unplanned actuation of the Primary Containment Group 3 1 solation, an Engineered Safety Feature (ESP), reportable in accordance with 10CFR50.73(a)(2)(iv).

D.

Ganig Procedures less than adequate. The isolation resulted from insufficient throttling of the RWCU MOV M074 valvo.

This allowed the combined flow from both pumps to exceed the setpoint of the isolation switch.

The cause of the insufficient throttling of the RWCU MOV M074 valve is the lack of Control Room flow indication when the Filter /Demineralizers are removed from service. Valvo position was set using the available pump discharge pressure indication.

E,

Safety significance

The RWCU high-flow isolation serves to protect against the consequences of significant leakage from the RWCU system. The automatic closure of the RWCU inlet isolation valves upon actuation of the high flow isolation protects the core by preventing continued inventory losses through a break.

In this event, an RWCU break had not occurred.

Consequently. actuation of the Croup 3 isolation was not required for core protection. Upon sensing a high flow signal, the isolation occurred as' designed.

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Safety Implications The effect of a high flow isolation at other plant conditions would not be significantly different.

In the event of an isolation with the RWCU pumps operating, the pumps automatically trip.

Removal of the RWCU System from operdtion has minimal safety implications.

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Corrective Action

The Group 3 isolation was reset, and the B pump placed into operation.

The system operating procedure will be revised to direct the une of local flow indications when shifting pumps with the Filter /

Demineralizers isolated.

H.

Eigilar Events None - previous high flow actuations of the Group 3 isolation circuitry have been caused by flashing of the hot fluid at the pump suction during plant cooldown or as a result of volds within system components.

The corrective actions for these events is not applicable to this occurrence, eve r sesA uso

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