Information Notice 1997-38, Level-Sensing System Initiates Common-Mode Faulure of High-Pressure-Injection Pumps: Difference between revisions
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| issue date = 06/24/1997 | | issue date = 06/24/1997 | ||
| title = Level-Sensing System Initiates Common-Mode Faulure of High-Pressure-Injection Pumps | | title = Level-Sensing System Initiates Common-Mode Faulure of High-Pressure-Injection Pumps | ||
| author name = Slosson | | author name = Slosson M | ||
| author affiliation = NRC/NRR | | author affiliation = NRC/NRR | ||
| addressee name = | | addressee name = | ||
Revision as of 06:39, 14 July 2019
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
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 KU 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
To receive a co of this document.
indicate In the box C=Coov wlo attachmentlendosure
E=Coov with attachment/endosure
N = No coy OFFICE Tech x HICB* x PECB* DRPM Contacts*NAME NFields JWermiel AChaffee MSlosson 5___ __ __ TK oshy _ _ _ _ _ _ _ _ _ _DATE 06/09/97 06/09/97 06/12/97 V07 OFFICIAL KRCORU COPY-
I S .--4 K-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
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N = No copy OFFICE Tech x HICB* l x PECB* DRPM Contacts*
ll NAME NFields JWermiel AChaffee MSlosson TKoshy DATE 06/09/97 06/09/97 06112/97 4/ /97 OFFICIAL RECORD COPY~ 6171k
- I K'J 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 x HICB x PECB DRPM Contacts l 4.5-A C)l NAME NFields AT JWermiel J A haffee MSlosson.TKoshyA UW P 67 DATE 61 /97 OF FICAL 7 41 /97 OFFICIAL RECORD COPY