Information Notice 1997-38, Level-Sensing System Initiates Common-Mode Faulure of High-Pressure-Injection Pumps

Level-Sensing System Initiates Common-Mode Faulure of High-Pressure-Injection Pumps

ML031050514
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000349, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Crane
Issue date:	06/24/1997
From:	Slosson M Office of Nuclear Reactor Regulation
To:
References
IN-97-038, NUDOCS 9706200203
Download: ML031050514 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001

June 24, 1997

NRC INFORMATION NOTICE 97-38: LEVEL-SENSING SYSTEM INITIATES COMMON-

MODE FAILURE OF HIGH-PRESSURE-INJECTION

PUMPS

Addressees

All holders of operating licenses or construction permits for nuclear power reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert

addressees to a recent incident in which two high-pressure-injection (HPI) pumps were

damaged as a result of an inaccurate letdown storage tank (LDST) level-sensing system.

The inaccuracy was caused by a drained reference leg. As a result, an incorrect level was

displayed, permitting the pumps to take suction from an empty tank. It is expected that

recipients will review this information for applicability to their facilities and consider actions, as

appropriate. However, suggestions contained in this information notice are not NRC

requirements; therefore, no specific action or written response is required.

Descdrition of Circumstances

On May 3, 1997, the licensee for Oconee Unit 3 was conducting a planned shutdown to

inspect an HPI line. During cooldown of the plant, HPI pump 3B was operating in the reactor

coolant system (RCS) makeup mode. The pump's discharge pressure dropped to the "low'

pressure setpoint initiating the automatic start of standby HPI pump 3A. The operators later

secured pump 3A when reactor coolant pump (RCP) seal injection flow indicated "high". The

HPI header pressure decreased again. HPI pump 3A automatically restarted. The pump's

motor current began oscillating. The operators secured HPI pump 3B because of an

indication of low motor current. Shortly afterwards, HPI pump 3A was also secured when its

motor current decreased sharply. The licensee issued a Notification of an Unusual Event

because of the loss of two of the three HPI pumps.

The licensee later concluded that both HPI pumps became hydrogen bound and possibly

damaged when they took suction from an empty LDST even though adequate tank inventory

was indicated.

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IN 97-38

June 24, 1997 Discussion

The HPI pumps at Oconee perform the dual functions of RCS makeup and high-pressure

safety injection. These pumps normally take suction from the LDST (also referred to as the

makeup or volume control tank by other vendors). A 25-psi (172.4 kPa) hydrogen

overpressure is maintained in this tank to scavenge oxygen from the RCS.

During this event, two level transmitters monitored tank level. These transmitters produce

level alarms in the control room. The alarms alert operators to initiate makeup to the LDST.

Both level transmitters shared a common reference leg. Because the shared reference leg

was partially drained, the indicated letdown tank level remained at 9 inches above the

low-level alarm setpoint. The tank was actually empty, its contents having been depleted

during normal charging. Letdown tank level was investigated only after both HPI pumps

developed problems.

Indicated level in the control room was derived from the equivalent pressure difference

between the drained reference leg and the back pressure from the 25 psi hydrogen

overpressure in the LDST. Because both level instruments shared the common reference

leg, both gave the same erroneous indication. Therefore, operators failed to provide makeup

inventory to the LDST. Two of the three HPI pumps became gas-bound, cavitated, and, as a

result, were structurally damaged.

If an actual safety injection actuation occurs, the suction isolation valve to the LDST remains

open while the suction isolation valve to the borated water storage tank (BWST) opens on the

safety injection signal. All three HPI pumps receive a start signal and take suction on both

the LDST and the BWST. With the two tanks cross-tied, the potential existed for this event to

have caused the loss of all HPI pumps as a result of gas binding. Loss of all three HPI

pumps could prevent the successful mitigation of a loss of coolant accident. During normal

operations, loss of all HPI pumps would result in the loss of reactor coolant pump seal

injection, normal RCS makeup, and normal boration.

The level transmitters were last calibrated in February 1997. Sometime between that last

calibration and the event, a leak developed from a scored cap on a test connection that

drained the reference leg. The cap was used to isolate the test connection. A drained

reference leg or a reference leg with entrained air can result in incorrect level indication.

Incorrect level indication will prevent appropriate setpoints being reached when process

conditions demand, defeat critical automatic safety functions, and could mislead plant

operators into taking less than conservative actions.

Pressure and level sensors, in any safety-related application, that rely on a reference leg for

a differential pressure reading, are sensitive to changes in reference leg level. Normal

surveillances that Include only channel checks with other instruments sharing the reference

leg or transmitter calibrations with external hydrostatic test sets will not reveal the true

condition of the reference leg. In the absence of an automatic reference leg fill system, periodic verification of reference leg level based on the plant-specific environment is needed

to ensure the operational integrity of the critical systems that are relied upon for manual and

automatic functions.

IN 97-38 June 24, 1997 This information notice requires no specific action or written response. If you have any

questions about information in this notice, please contact one of the technical contacts listed

below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Thomas Koshy, NRR

301-415-1176 E-mail: txkenrc.gov

Nick Fields, NRR

301-415-1173 E-mail: enfenrc.gov

Attachment: List of Recently Issue

Information Notices

4'

ln.44

I

Attachment

IN 97-38

.June 24, 1997 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issuance

Issued to

96-53, Supp. 1

97-37

Retrofit to Amersham 660

Posilock Radiography

Camera to Correct Incon- sistency in 10 CFR Part 34

Compatibility

Main Transformer Fault

with Ensuing Oil Spill

into Turbine Building

06/23/97

06/20/97

All industrial radiography

licensees

All holders of OLs or CPs

for nuclear power reactors

97-36

97-35

97-34

Unplanned Intakes by

Worker of Transuranic

Airborne Radioactive

Materials and External

Exposure Due to Inadequate

Control of Work

Retrofit to Industrial

Nuclear Company (INC)

IR100 Radiography Camera

to Correct Inconsistency

in 10 CFR Part 34

Compatibility

Deficiencies in Licensee

Submittals Regarding

Terminology for Radio- logical Emergency Action

Levels in Accordance

With the New Part 20

06/20/97

06/18/97

06/12/97

All holders of OLs and CPs

permits. All licensees of

of nuclear power reactors

in the decommissioning

stage and fuel cycle

All industrial radiography

licensees

All holders of OLs or CPs

for test and research

reactors

OL = Operating License

CP = Construction Permit

I

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IN 97-38 June 24, 1997 This information notice requires no specific action or written response. If you have any

questions about information in this notice, please contact one of the technical contacts listed

below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.

original signed by S.H. Weiss for

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts:

Thomas Koshy, NRR

301-415-1176 E-mail: txk@nrc.gov

Nick Fields, NRR

301-415-1173 E-mail: enf@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

Tech Editor has reviewed and concurred on 5/14197 DOCUMENT NAME: G:XNICKIOCONEE.IN

• SEE PREVIOUS CONCURRENCES

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of this document. indicate In the box C=Coov wlo attachmentlendosure E=Coov with attachment/endosure N = No coy

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DATE

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06/09/97

06/12/97 V07

OFFICIAL KRCORU COPY

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IN 97-xx

June xx, 1997 This information notice requires no specific action or written response. If you have any

questions about information in this notice, please contact one of the technical contacts listed

below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Thomas Koshy, NRR

301-415-1176 E-mail: txk@nrc.gov

Nick Fields, NRR

301-415-1173 E-mail: enfenrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:%NICKkOCONEE.IN

• SEE PREVIOUS CONCURRENCES

To receive a conv of this document indicate in the box C=Coov wlo attachmentlenclosure E=Coov with attachmentlenclosure N = No copy

OFFICE

Tech

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HICB*

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PECB*

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Contacts*

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NAME

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DATE

06/09/97

06/09/97

06112/97

4/ /97

OFFICIAL RECORD COPY

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IN 97-xx

June xx, 1997 This information notice requires no specific action or written response. If you have any

questions about information in this notice, please contact on6 of the technical contacts listed

below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical Contacts: Thomas Koshy, NRR

301-415-1176 e-mail:txk@nrc.gov

Nick Fields, NRR

301-415-1173 e-mail:enfenrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\\NICK\\OCONEE.IN

To receive a copy of tis document, indicate in the box C=Copy wlo attachment/enclosure E=Copy with attachment/enclosure N = No copy

OFFICE

Tech

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