Information Notice 1997-40, Potential Nitrogen Accumulation Resulting from Backleakage from Safety Injection Tanks
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UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001
June 26, 1997
POTENTIAL NITROGEN ACCUMULATION
RESULTING FROM BACKLEAKAGE FROM SAFETY
INJECTION TANKS
Addressees
All holders of operating licenses or construction permits for pressurized-water reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert
addressees to potential nitrogen accumulation in interfacing systems resulting from
backleakage from safety injection tanks (SITs). It is expected that recipients will review the
information for applicability to their facilities and consider actions, as appropriate, to avoid
similar problems. However, suggestions contained in this information notice are not NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances
Waterford
On November 19 and 21, 1996, Waterford Generating Station, Unit 3, experienced
waterhammer events on the low-pressure safety injection (LPSI) B train. On November 19,
1996, the control room pressure gauge was observed to spike to approximately 3.55 MPa
[500 psig] (normal operating pressure is approximately 1.2 MPa [160 psig]). On
November 21, 1996, the train B piping was vented, and a strip chart recorder was installed to
monitor pressure. A pressure of 4.65 MPa [660 psig] was observed following the start of the
pump. Shortly thereafter, the LPSI train B flow control valve was found partially open
because of a valve mispositioning error by the operations crew. The valve was closed, and
the pump started without a pressure transient. Apparently no structural damage resulted
from the waterhammer events.
On December 13, 1996, LPSI train A experienced a waterhammer event. During a routine
surveillance run of LPSI pump A, the pressure spiked to approximately 2.3 MPa [317 psig].
The licensee's investigation after this event utilized ultrasonic testing (UT) to inspect high
points in the LPSI piping. The licensee identified gas voiding in the horizontal run of the two
A train injection lines of 30.5 cm [12 inches] and 35.5 cm [14 inches) of arc. The injection
lines are 20 cm [8 inches] in diameter. The gas was sampled and found to be approximately
97 percent nitrogen. The licensee concluded that nitrogen-saturated water from the SIT (the
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June 26, 1997 The gas was vented from the A train of LPSI, and LPSI was declared operable on
December 14, 1996. On December 18, 1996, voiding was found in LPSI train B piping, with
arcs of 28 cm (11 inchesl and 25.4 cm [10 inches]. Because of the location of these gas
pockets, the licensee was unable to vent these lines. The licensee performed an operability
evaluation and concluded that the B train remained operable but instituted a UT surveillance
program to inspect the voids every 3 days and identified acceptance criteria for an
acceptable arc length. Furthermore, the licensee was pursuing a design modification to
install high-point vents.
In February 1997, the licensee noted that one of its SITs was experiencing a lowering in
level. Upon investigation, the licensee found that a LPSI system containment isolation valve
was off its shut seat. The licensee surmised that water was leaking from the SIT past check
valves and the partially open isolation valve in the LPSI to the refueling water storage pool
(RWSP). On February 20, 1997, the licensee conducted testing on the isolation valve to
investigate why the valve was not shut. The licensee cycled the valve several times during
the course of this testing. At the completion of the testing, the licensee performed UT of the
A LPSI injection line to check for voiding.
The licensee found that the high horizontal run of piping was dry and that a void extended
203 cm [80 inches) down the vertical run of piping. In response to the large void, the
licensee used a vacuum pump to draw water into the line until the voiding was reduced to a
12.7-cm [5-inch] arc. The reduced arc was within the licensee's acceptance criteria for this
line, and LPSI was declared operable.
The licensee also postulated that the shutdown cooling heat exchanger isolation valves may
be susceptible to waterhammer-induced pressure locking. The isolation valves had been
previously evaluated for a trapped bonnet pressure of 2.2 MPa [300 psig] and found to be
operable. However, there is no assurance that bonnet pressure would not exceed 2.2 MPa
[300 psig] when subjected to a waterhammer pressure surge. There is no evidence that this
pressure locking has occurred in the past, and the licensee believes that this scenario is
unlikely. However, the postulated phenomenon could result in common-mode failure of the
heat exchangers, and the licensee has installed bonnet pressure relief devices.
Sequoyah
In January 1995, during a Sequoyah Unit I scheduled quarterly residual heat removal (RHR)
pump test, a loud metallic noise was heard and movement of the refueling water storage tank
(RWST) suction piping was observed. At the time when the noise was heard and pipe
movement observed, personnel were performing a walkdown of a previously identified
damaged RHR pipe hanger. The RHR system piping was subsequently inspected for gas
voids and approximately .23 cubic meters (8 cubic feet] of gas was identified. A sample
taken of the vented gas determined the gas to be approximately 98 percent nitrogen. The
license believed that the source of the gas was one or more of the Emergency Core Cooling
System (ECCS) Cold Leg Accumulators (CLA) and that there were two potential leakage
June 26, 1997 paths that water could travel from the CLAs to the RHR injection piping where the nitrogen
gas came out of solution: through the Safety Injection System (SIS) test header and/or
through the secondary check valves on the RHR cold leg Injection lines to the Reactor
Coolant System (RCS). The licensee performed an operability evaluation which determined
that the gas did not affect operability of the RHR system either in normal or accident
conditions.
Over the course of the next several months the licensee periodically vented the RHR piping, monitored the rate of gas accumulation and calculated the gas volume in the RHR piping, and tracked the level decrease of the CLAs. To date, the licensee has not been successful
in identifying and correcting leaking isolation valves in the SIS test header. The Sequoyah
RHR system design and layout may have contributed to the gas accumulation due to the lack
of high point vents in the RHR system and the difficult accessibility of those vents which
were available. In November 1996, the licensee installed a manual vent in the Unit 1 A train
RHR system in a 49 meter 1160 footl section of piping which previously was not completely
ventable.
In October 1996, an analysis of the Unit 1 RHR piping system was performed to determine
the imposed forces resulting from system operation with various volumes of gas in the piping
system. The analysis concluded that the hydraulic forces built up are higher with increasing
volumes of gas but level off when the gas volumes go beyond more than .28 cubic meters
[10 cubic feet). The measured volumes of gas in the Unit 1 RHR system have varied from
approximately .23 cubic meters [8 cubic feet] to .4 cubic meters [14 cubic feet]. The licensee
also calculated that for each gallon of water released from the CLAs, approximately 2.1 liters
[0.073 cubic feet] of gas is released.
Discussion
If SITs or CLAs lose water level, nitrogen gas accumulation could be occurring in interfacing
systems. The presence of large amounts of gas in discharge piping creates the possibility of
waterhammer with potentially significant consequences. Waterhammer of sufficient magni- tude can cause common-mode failure of safety injection trains. Structural failure of the
discharge piping could create a containment bypass release path in addition to preventing
safety injection flow. Additionally, a waterhammer event could potentially cause pressure
locking in some valves. A plant's susceptibility to nitrogen accumulation in the ECCS lines is
dependent on a number of plant-specific factors, including operating pressure of the SITs or
CLAs, elevations and orientation of ECCS injection lines, and the elevation of the RWSP or
RWST. Licensees may wish to evaluate the possibility and effect of gas accumulation on
potentially susceptible systems. Licensees may also wish to evaluate the design of these
systems to ensure adequate venting capability.
June 26, 1997 This information notice requires no specific action or written response. If you have any
questions about the 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:
Robert D. Starkey, RII
(423) 842-8001 E-mail: drs@nrc.gov
Christopher Jackson, NRR
301-415-2947 E-mail: cpj@nrc.gov
Phillip Harrell, RIV
(817) 860-8250
E-mail: phhenrc.gov
John Tappert, NRR
301415-1167 E-mail: jrt@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
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Attachment
June 26, 1997 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
97-39
97-38
96-53, Supp. 1
Inadequate 10 CFR 72.48
Safety Evaluations of
Independent Spent Fuel
Storage Installations
Level-Sensing System
Initiates Common-Mode
Failure of High-Pressure-
Injection Pumps
Retrofit to Amersham 660
Posilock Radiography
Camera to Correct Incon- sistency in 10 CFR Part 34
Compatibility
06/26/97
06/24/97
06/23/97
All holders of OLs or CPs
for nuclear power reactors.
All holders of licenses for
independent spent fuel
storage installations
All holders of OLs or CPs
for nuclear power reactors
All industrial radiography
licensees
97-37
97-36
Main Transformer Fault
with Ensuing Oil Spill
into Turbine Building
Unplanned Intakes by
Worker of Transuranic
Airborne Radioactive
Materials and External
Exposure Due to Inadequate
Control of Work
06/20/97
06/20/97
All holders of OLs or CPs
for nuclear power reactors
All holders of OLs and CPs
permits. All licensees of
of nuclear power reactors
in the decommissioning
stage and fuel cycle
97-35
Retrofit to Industrial
Nuclear Company (INC)
IR100 Radiography Camera
to Correct Inconsistency
Compatibility
06/18/97
All industrial radiography
licensees
OL = Operating License
CP = Construction Permit
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June 26, 1997 This information notice requires no specific action or written response. If you have any
questions about the 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:
Robert D. Starkey, RII
(423) 842-8001 E-mail: drs@nrc.gov
Christopher Jackson, NRR
301-415-2947 E-mail: cpj@nrc.gov
Phillip Harrell, RIV
(817) 860-8250
E-mail: phh@nrc.gov
John Tappert, NRR
301-415-1167 E-mail: jrt@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
Tech Editor reviewed 3131/97 DOCUMENT NAME: 97-40.IN
OFFICE
Contacts
C/SRXB:DSSA
C/PECB:DRPM
(A)DIDRPM
NAME
RStarkey
JLyons*
AChaffee*
MSlosson
CJackson*
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PHarrell*
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_
_
JTappert*
DATE
04/22/87
05/11/97
06/04/97
06t097
Official Rec ord Copy
IN 97-xx
June xx, 1997 This information notice requires no specific action or written response. If you have any
questions about the 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:
Robert D. Starkey, Ril
(423) 842-8001 E-mail: drs@nrc.gov
Christopher Jackson, NRR
301-415-2947 E-mail: cpj@nrc.gov
Phillip Harrell, RIV
(817) 8604250
E-mail: phh@nrc.gov
John Tappert, NRR
301415-1 167 E-mail: jrtenrc.gov
Attachment: List of Recently Issued NRC Information Notices
Tech Editor reviewed 3/31/97 DOCUMENT NAME: G:URT1N2VOID.IN
OFFICE
Contacts
C/SRXB:DSSA
CIPECB:DRPM
(A)D/DRPM
NAME
RStarkey
JLyons*
AChaffee
MSlosson
CJackson*
PHarrell*
_
JTappert2
05111/97
5/____51_/97 DAE 04/22/87
105/11/97
5/ /97
15/ /97
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K2 IN 97-xx
May xx, 1997 This information notice requires no specific action or written response. If you have any
questions about the 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:
Robert D. Starkey, RII
(423) 842-8001 E-mail: drs@nrc.gov
Christopher Jackson, NRR
(301) 415-2947 E-mail: cpj@nrc.gov
Phillip Harrell, RIV
(817) 860-8250
E-mail: phh@nrc.gov
John Tappert, NRR
(301) 415-1167 E-mail: jrt@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
Tech Editor reviewed 3131/97 DOCUMENT NAME: G:VRTN2VOID.IN
OFFICE
Contacts
C/SRXB:DSSA
C/PECB:DRPM
(A)D/DRPM
NAME
RStarkey
JLyons*AChaffee
MSlosson
CJackson*
PHarrell*
JTappert*
_
DATE
04/22/87
05111/97
5/ 197
5/ 197
Official Record Copy Ad
IN 97-xx
May xx, 1997 This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manage
Marylee M. Slosson, Acting Direor
Division of Reactor Program
nagement
Office of Nuclear Reactor
gulation
Technical contacts:
Robert D. Starkey, RII
Christopher Jac on, NRR
(423) 842-8001
(301) 415-29 E-mail: drs@nrc.gov
E-mail: cpj
nrc.gov
Phillip Harrell, RIV
John appert, NRR
(817) 860-8250
(30
415-1167 E-mail: phh@nrc.gov
E ail: jrt@nrc.gov
Attachment: List of Recently Issued NRC Inform tion Notices
Tech Editor reviewed 3/3147 DOCUMENT NAME: G:
ThN2VOID.IN
OFFICE
Contacts
/
CISRXB:DSSA
C/PECB:DRPM
(A)DIDRPM
NAME
RStarkey
JLyons*
AChaffee
MSlosson
CJacks
PHarre
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DATE
042/87
05/11/97
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IN 97-xx
May xx, 1997 This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project
age
Marylee M. Slosson, Acting irector
Division of Reactor ProgrT
Management
Office of Nuclear Rea
r Regulation
Technical contacts:
Robert D. Starkey, RII
Christophe ackson, NRR
(423) 842-8001
(301) 41 -2947 E-mail: drs@nrc.gov
E-maillcpjnrc.gov
Phillip Harrell, RIV
ohn Tappert, NRR
(817) 860-8250
(301) 415-1167 E-mail: phh@nrc.gov
E-mail: jrt@nrc.gov
Attachment: List of Recently Issued NR
nformation Notices
Tech Editor revie ed 3/31/97 DOCUMENT N ME: G:URTRN2VOID.IN
OFFICE I
ntacts
C/SRXB:DSSA
CIPECB:DRPM
D/DRPM
NAME
/RStarkey
JLyons*
AChaffee
TMartin
CJackson*
/ PHarreli*
JTappert*
DATE
04/22/87
05111/97
Official Record Co3W4497
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IN 97-xx
May xx, 1997 This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts:
Robert D. Starkey, Region II
(423) 842-8001 E-mail: drs@nrc.gov
Christopher Jackson, NRR
(301) 415-2947 E-mail: cpjenrc.gov
Phillip Harrell, Region IV
(817) 860-8250
E-mail: phhenrc.gov
John Tappert, NRR
(301) 415-1167 E-mail: jrtenrc.gov
Attachment: List of Recently Issued NRC Information Notices
Tech Editor reviewed 3131/97 DOCUMENT NAME: G:AJRTNN2VOID.IN
OFFICE
Contacts
C/SRXB:DSSA
CIPECB:DRPM
DIDRPM
NAME
RStarkey
JLyons*
AChaffee
TMartin
CJackson*
PHarrell*
JTappert*
DATE
04122/87
05/11/97
'J13 I
Official Record Copy
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IN 97-xx
April xx, 1997 This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts:
Robert D. Starkey, Region II
(423) 842-8001 E-mail: drs@nrc.gov
Christopher Jackson, NRR
(301) 415-2947 E-mail: cpj@nrc.gov
Phillip Harrell, Region IV
(817) 860-8250
E-mail: phh@nrc.gov
John Tappert, NRR
(301) 415-1167 E-mail: jrt@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
Tech Editor reviewed 3/31/97 DOCUMENT NAME: G:\\JRT\\N2VOID.IN
OFFICE
Contacts
C/SRXB:DSSA
C/PECB: DRPM
D/DRPM
NAME
RStarkey -$1YA
'J'JLo4 I L144 AChaffee
TMartin
CJacksonV
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PHarrel ^1 X
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JTappert
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