05000458/LER-1986-001, :on 860101,unit Scrammed from 19% Power on Low Reactor Water Level as Result of Isolations on Both Low Pressure Feedwater Heater Strings.Probably Caused by Flashing in Level Transmitter Pots

:on 860101,unit Scrammed from 19% Power on Low Reactor Water Level as Result of Isolations on Both Low Pressure Feedwater Heater Strings.Probably Caused by Flashing in Level Transmitter Pots

ML20196C278
Person / Time
Site:	River Bend
Issue date:	06/24/1988
From:	Booker J, England L GULF STATES UTILITIES CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
LER-86-001, LER-86-1, RBG-28161, NUDOCS 8807010050
Download: ML20196C278 (4)

LER-1986-001, on 860101,unit Scrammed from 19% Power on Low Reactor Water Level as Result of Isolations on Both Low Pressure Feedwater Heater Strings.Probably Caused by Flashing in Level Transmitter Pots

Event date:
Report date:
4581986001R00 - NRC Website

text

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On 01/01/86 at 0354 thgyunit scrammed from 19 percent power on low reactor water level (level 3).

The low level scram was a result of isolations on both low pressure feedwater heater strings coincident with a failure of the low pressure feedwater heater bypass valve to open.

At 0356 Reactor Core Isolation Cooling was started and used to restore level prior to reaching the initiation level for High Pressure Core Spray.

An investigation into the event was conducted.

It was determined that the probable cause for the isolations was flashing in the level transmitter pots causing high level spikes.

It is believed that the failure of the bypass valve to open was a result of thermal binding causing the motor operator circuit breaker to trip on overload.

There were no safety consequences or implications to the public as a result of this event.

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.ac e u nn On 01/01/86 at 0354 the unit scrammed from 19 percent thermal power on low level (level 3) due to a loss of all feedwater flow.

Apparently a spurious high-high level in the

'A' Sth point low pressure feedwater heater (*HX*) tripped causing condensate flow to the

'A' string to I

isolate.

The

'B' low pressure heater string had previously isolated and gone undetected. It is believed to have been caused by a similar l

spurious signal which may have caused the

'A' heater string to isolate.

The low pressure heater string bypass valve (*V*) failed to I automatically open on either

'A' or

'B' heater string isolation.

Its breaker (*BXR*) was found tripped.

This resulted in a complete isolation of condensate flow to the feed pumps

(*P*) and a loss of feedwater flow to the vessel.

The feedwater pumps are designed to trip on low suction pressure; however, feedwater pump

'A' failed to trip and ran for approximately five minutes before condensate flow was restored.

At 0356 the Reactor Core Isolation Cooling (RJIC)

(*BN*)

l system was started and used to rectore level prior to reaching the initiation level for High Pressure Core Spray (HPCS

(*BG*).

l l

Upon thorough investigation of all associated feedwater heater train instrumentation and logic, with no apparent problems discovered, it was determined the probable cause to be flashing in the level transmitter (*LT*) pots causing high level spikes.

Failure of the low l pressure heater string bypass valve to open was also investigated.

It is possible that during system heat up the bypass val.ve may have thermally bound and caused the motor (*MO*) overload.

l Corrective action has been taken to ensure condensate pots for level transmitters are filled.

These level transmitters have been instrumented with a strip recorder (*LR*) to monitor for similar l

occurrences.

The low pressure heater bypass valve motor overload has been reset from its lower current setting to its upper setpoint.

Additionally, General Operating Procedure (GOP)-0001 "Plant Startup to l Low Power Alarm Point" has been revised to require the bypass valve to be left in the open position until approximately 15 percent power to prevent valve binding during system heatup.

Finally, human factors design changes have been initiated via Modification Requests (MRs) l 86-0015, 0016, and 0017 to highlight heater level alarms and trip indicators for the heater bypass valve.

MR 86-0015, highlighting the heater level alarms, was completed on 8/20/86.

System performance has been satisfactory since completion of the MR.

MRs 86-0016, installation of indicating lights for out of service feedwater system, and 96-0017, a trip indicator for heater bypass valves, has been re-evaluated considering the additional huraan factors draign change.

Based on the decreased probability for human error af ter imnlementation of MR 86-0015 and satisfactory system performance since the reported event, these additional modifications have been determined to be unnecessary and will not be imp.1.emented at this time,

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w i ms4unn There were no safety consequences or implications to the public because the unit was placed in a safe shutdown condition, and water level was quickly restored via the RCIC system.

Furthermore, redundant Emergency Core Cooling Systems (ECCS) were available at all times as an additional source of coolant if necessary.

NOTE:

Energy Industry Identification System Codes are idertified in the test as (*XX*).

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O GULF STATES UTILITIES COMPANY RfVfR BEND STAfiON POST OFFICE Bor 220 ST FRANCISvitLE LOutSIANA '0775 ARE A CODE 504 635 6094 346-8651 June 24, 1988 RBG-28161 File Nos. G9.5, G9.25.1.3 l

U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C.

20555 Gentlemen:

River Bend Station - Unit 1 Docket No. 50-458 Please find enclosed Licensee Event Report No.86-001 Revision 1 for River Bend Station - Unit 1.

This report is being submitted to provide updated information on corrective action.

Sincerely, f.

s J. E.

Booker Manager-River Bend Oversight River Bend Nuclear Group cc:

U.S. Nuclear Regulatory Commission 611 Ryan Plara Drive, Suite 1000 Arlington, TX 76011 NRC Resident Inspector P.O. Box 1051 St. Francisville, LA 70775 INPO Records Center 1100 Circle 75 Parkway Atlanta, GA 30339-3064 I