Information Notice 1993-90, Unisolatable Reactor Coolant System Leak Following Repeated Appeated Applications of Leak Sealant
Ie UNITED STATES NUCLEAR REGULATORY
COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555 December 1, 1993 NRC INFORMATION
NOTICE 93-90: UNISOLATABLE
REACTOR COOLANT SYSTEM LEAK FOLLOWING
REPEATED APPLICATIONS
OF LEAK SEALANT
Addressees
All holders of operating
licenses or construction
permits for nuclear power reactors.PurDose The U.S. Nuclear Regulatory
Commission (NRC) is issuing this information
notice to alert addressees
to an application
of an on-line leak sealing process which substantially
degraded the integrity
of the reactor coolant pressure boundary.
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
On May 24, 1993, at the Millstone
Nuclear Power Station, Unit 2, Northeast Utilities (the licensee)
identified
a leak in a body-to-bonnet
gasket on valve 2-CH-442.
This valve is a Velan 2-inch gate valve which is used to manually isolate the letdown portion of the chemical and volume control system from the reactor coolant system for maintenance
and local leak rate testing of containment
isolation
valves. The valve is upstream of the automatic
letdown isolation
valves, and itself cannot be isolated from the reactor coolant system. Between June 4, and August 5, 1993, leak sealant was injected approximately
30 times in an attempt to stop the leakage from the body-to-bonnet joint. Five sealant injections
were performed
by Leak Repairs, Inc., and the remainder
were performed
by Furmanite, Inc.; these activities
were performed
under the direction
of the licensee.
The injections
had marginal results; after sealing, the valve would remain leak free for various periods ranging up to 18 days in length and would then start to leak again.On June 12, 1993, following
the 7th leak-seal
injection, technicians
attempted to install a body-to-bonnet
peripheral
clamp to provide a boundary for the leak-sealant
compound.
The clamp could not be installed
because of fit-up problems with the irregularly
shaped valve bonnet. The bonnet had been installed
90 degrees away from its normal orientation, further complicating
9311190455 Pl k Its Mattel I:- O lo ql ol 0
IN 93-90 December 1, 1993 the attempted
clamp installation.
Subsequent
on-line attempts to seal the leak included mechanical
peening to prevent injection
material from extruding out of the gasket area. This peening closed the body-to-bonnet
joint.On August 5, 1993, leak sealant was injected to obtain the dry valve surfaces required for welding a second (hybrid) clamp across the body-to-bonnet
joint.During the injection, technicians
observed that the leakage increased dramatically, from slight seepage to a 3.1-meter
[10-foot]
steam jet. The technicians
also reported that the valve bonnet appeared to lift and that one body-to-bonnet
stud moved. In response to the increased
leakage, the Director of Millstone, Unit 2, ordered a controlled
normal shutdown.
During the shutdown, the maximum reactor coolant system leakage was 16.3 liters[4.3 gallons] per minute.Discussion
When valve 2-CH-442 was disassembled, it was discovered
that one stud was broken. Because the body of valve 2-CH-442 is an unisolatable
reactor coolant system pressure boundary, the broken stud changed the character
of the incident from a routine gasket-related
failure to a significant
structural
failure. An ABB-CE metallurgical
study indicates
that the stud broke in response to loads applied as part of the on-line leak sealing process. The most likely potential
sources of loads were evaluated.
These likely load sources are: (1) drilling, tapping, and injection
port installation, (2) peening, and (3) injecting.
Subsequent
testing performed
for the licensee at the ABB-CE facility indicated
that stud loads produced by drilling, tapping, and injection
port installation
were moderate.
However, when body-to-bonnet
Joints are peened to the point that the edges contact, the adjacent bolt can be loaded to failure due to the wedging action of the deformed metal.Inspection
revealed that two of the four studs had drill holes in them from the injection
port and clamp installation
drilling processes.
The broken stud and one other stud each had 0.49 centimeter
[0.19 inch] diameter holes that penetrated
0.25 centimeter
[0.10 inch] and 0.28 centimeter
[0.11 inch] deep, respectively.
The holes did not appear to contribute
to the stud failure.The licensee had intended to limit the injection
port locations
to low stress zones. However, the injection
ports had actually been drilled in restricted
high-stress
zones located near the studs. Later analysis determined
that the drilling caused very little stress on the studs.The leak-sealant
injection
procedure
at Millstone
permitted
some peening between the body and bonnet to prevent sealant extrusion (it did not allow peening along the entire perimeter
of the valve). Inspection
of valve 2-CH-442 revealed a significant
amount of metal moved by the peening process.Peening essentially
obscured the body-to-bonnet
interface, leaving a groove-like indentation
along the split line, and metal was peened so that it was in contact with all four bonnet studs. In addition, chisel-like
marks were
IN 93-90;' _December
1, 1993 evident around the leak-sealant
injection
ports where hand peening was performed.
The licensee determined
that the extensive
peening was responsible
for the stud failure.The licensee had made no provision
to limit the amount of leak sealant injected into the valve. As a result, a total of approximately
2.16 liters[0.57 gallon] of leak sealant was injected into the body-to-bonnet
joint.The repeated attempts to seal the valve at Millstone
Unit 2 indicated
that an adequate engineering
evaluation
was not performed.
The licensee evaluation
did not adequately
consider the effects of the sealing process and the borated water on the fasteners.
Also, the evaluation
did not adequately
consider the amount or effect of sealant entering the system after repeated injections.
Further, the evaluation
did not adequately
consider the operational
and safety consequences
of structural
failure of the component
or the fasteners
during and after the leak-seal
attempts.
In addition, management
and quality assurance
oversight
did not identify the failures to follow procedures, the failures to adhere to engineering
documents
and the lack of weight given to personnel
safety considerations.
Events such as the one discussed
above have the potential
to cause a loss-of-coolant accident and to result in personnel
injury or death. This event illustrates
the importance
of properly performed
engineering
and safety evaluations
and the importance
of considering
occupational
safety hazards in support of on-line leak sealant use. When ASME Code Class 1 pressure boundary components
are involved, these considerations
are especially
important
to public safety.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.Brian K. Grimes, Director Division of Operating
Reactor Support Office of Nuclear Reactor Regulation
Technical
contacts:
Eric J. Benner, NRR (301) 504-1171 Geoffrey P. Hornseth, NRR (301) 504-2756 Charles G. Hammer, NRR (301) 504-2791 Attachment:
List of Recently Issued NRC Information
Notices
\- I I ichment rtr'93-90 December 1, 1993 LIST OF RECENTLY ISSUED NRC INFORMATION
NOTICES Information
Date of Notice No. Subject Issuance Issued to 93-89 Potential
Problems with BWR Level Instrumentation
Backfill Modifications
11/26/93 All holders of OLs or CPs for boiling water reactors.93-88 93-86 93-85 Status of Motor-Operated
Valve Performance
Pre-diction Program by the Electric Power Research Institute Fuse Problems with Westinghouse
7300 Printed Circuit Cards Identification
of Iso-topes in the Production
and Shipment of Byproduct Material at Non-power Reactors Problems with X-Relays in DB- and DHB-Type Circuit Breakers Manu-factured by Westinghouse
Determination
of Westing-house Reactor Coolant Pump Seal Failure 11/30/93 11/04/93 10/29/93 10/20/93 10/20/93 All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for test and research reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for pressurized
water reactors (PWRs).93-84 93-83 Potential
Loss of Spent Fuel Pool Cooling Following
A Loss of Coolant Accident (LOCA)10/07/93 All holders for boiling (BWRs).of OLs or CPs water reactors 93-82 Recent Fuel and Core Performance
Problems in Operating
Reactors 10/12/93 All holders of OLs or CPs for nuclear power reactors and all NRC-approved
fuel suppliers.
OL = Operating
License CP = Construction
Permit
IN 93-90 K_, <g December 1, 1993 evident around the leak-sealant
injection
ports where hand peening was performed.
The licensee determined
that the extensive
peening was responsible
for the stud failure.The licensee had made no provision
to limit the amount of leak sealant injected into the valve. As a result, a total of approximately
2.16 liters[0.57 gallon] of leak sealant was injected into the body-to-bonnet
joint.The repeated attempts to seal the valve at Millstone
Unit 2 indicated
that an adequate engineering
evaluation
was not performed.
The licensee evaluation
did not adequately
consider the effects of the sealing process and the borated water on the fasteners.
Also, the evaluation
did not adequately
consider the amount or effect of sealant entering the system after repeated injections.
Further, the evaluation
did not adequately
consider the operational
and safety consequences
of structural
failure of the component
or the fasteners
during and after the leak-seal
attempts.
In addition, management
and quality assurance
oversight
did not identify the failures to follow procedures, the failures to adhere to engineering
documents
and the lack of weight given to personnel
safety considerations.
Events such as the one discussed
above have the potential
to cause a loss-of-coolant accident and to result in personnel
injury or death. This event illustrates
the importance
of considering
occupational
safety hazards as well as the importance
of properly performed
engineering
and safety evaluations
in support of on-line leak sealant use. When ASME Code Class 1 pressure boundary components
are involved, these considerations
are especially
important
to public safety.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.orig /s/'d by BKGrimes Brian K. Grimes, Director Division of Operating
Reactor Support Office of Nuclear Reactor Regulation
Technical
contacts:
Eric J. Benner, NRR (301) 504-1171 Geoffrey P. Hornseth, NRR (301) 504-2756 Charles G. Hammer, NRR (301) 504-2791 Attachment:
List of Recently Issued NRC Information
Notices Resident Inspector (DAD) reviewed via E-mail on 10/22/93* See attached page for previous concurrences
Concurrence
page for"--rN 93-90 Di-avinisc
rnnmirrIncrP
fnr IN 93-90 I OFC OEAB:DORS
SC/OEAB:DORS
EMCB:DE C/EMCB:DE NAME EBenner* EGoodwin*
GHornseth*
JStrosnider*
DATE 11/2/93 10/19/93 11/2/93 __ 11/4/93 OFC EMEB:DE C/EMEB:DE
DEPUB:ADM NAME GHammer* JNorberg*
JWiggins*
Tech Ed*DATE 11/2/93 11/4/93 11/4/93 11/05/93 OFC C/OEAB:DORS*
OGCB:DORS
C/OGCB:DORS*
r NAME AChaffee PWen*GMarcus
DATE 11/17/93 11/19/93 11/23/93 P/4/93[OFFICIAL
RECORD LUPYJ DOCUMENT NAME: 93-90.IN
IN 93-XX November xx, 1993 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.Brian K. Grimes, Director Division of Operating
Reactor Support Office of Nuclear Reactor Regulation
Technical
contacts: Eric J. Benner, NRR (301) 504-1171 Geoffrey P. Hornseth, NRR (301) 504-2756 Charles G. Hammer, NRR (301) 504-2791 Attachment:
List of Recently Issued NRC Information
Notices Resident Inspector (DAD) reviewed via E-mail on 10/22/93* See Previous Concurrence
OFC OEAB:DORS
SC/OEAB:DORS
EMCB:DE C/EMCB:DE NAME EBenner* EGoodwin*
GHornseth*
JStrosnider*
DATE j 11/2/93 10/19/93 11/2/93 11/4/93 OFC EMEB:DE C/EMEB:DE
D/DE PUB:ADM NAME GHammer* JNorberg*
JWiggins*
Tech Ed*DATE 11/2/93 11/4/93 11/4/93 111/05/93 OFC C/OEAB:DORS*
OGCB:DORS
C/OGCB:DORS
D/DORS NAME AChaffee PWen* GMarcus MHt1 BGrimes DATE 11/17/93 11/19/93 1Il/ag/93
1 93[OFFICIAL
RECORD COPY]DOCUMENT NAME:MILLSTON.WEN
)
IN 93-XX November xx, 1993 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.Brian K. Grimes, Director Division of Op ating Reactor Support Office of Nuc ear Reactor Regulation
Technical
contacts:
Eric J. Benner, NRR (301) 504-1171 Geoffrey P. Hornset , RR (301) 504-2756 Charles G. Hammer, RR (301) 504-2791 Attachment:
List of Recently Issu d NRC Informat n Notices Resident Inspector (DAD) revie d via E-mail on 10/22/* See Previous Concurrence
OFC OEAB:DORS
S OEAB:DORS
EMCB:DE C/EMCB:DE NAME EBennerX-
/EGoodwin*
GHornseth*
JStrosnider*
DATE 11/2/93 10/19/93 11/2/93 1 11/4/93 OFC EMEB:DE C/EMEB:DE
D/DE PUB:ADM NAME GHammer* JNorberg*
JWiggins*
Tech Ed*DATE , 11/2/93 11/4/93 11/4/93 11/05/93 OFC C/OEAB:DORS*
OGCB:DORS
C/OGCB:DORS
D/DORS NAME AChaffee PWen GMarcus BGrimes DATE 11/17/93 / /jg/93 / /93 / 93[OFFICIAL
RECORD COPY]DOCUMENT NAME:MILLSTON.WEN
' IN 93-XX November xx, 1993 At this time, the licensee is developing
significant
new information
about the effects of excessive
peening. Ongoing laboratory
experiments
are showing that when body-to-bonnet
joints are peened to the point that the edges contact, the adjacent bolt can be loaded to failure. This is apparently
due to the wedging action of the deformed metal.This information
notice requires no specific actio For written response.
If you have any questions
about the information
in t is notice, please contact the technical
contact listed below or the approp iate Office of Nuclear Reactor Regulation (NRR) project manager.Brian .Grimes, Director Divison of Operating
Reactor Support Off e of Nuclear Reactor Regulation
Technical
contact: Eric J. Benner, (301) 504-1171 Attachment:
List of Recently Iss ed NRC m ormation Notices Resident Inspector (DAD) eviewed via E-mail on 10/22/93* See Previous Concurrence
OFC OEAB:DORS
_ SC/OEAB:DORS
EMCB:DE l C/EMCB:DE NAME EBenner l EGoodwin*
GHornseth*
JStrosnider*
DATE 111/2/93 1 10/19/93 ,11/2/93 j 11/4/93 OFC EMEB:DE C/EMEB:DE
D/DE PUB:ADM NAME GHammer* JNorberg*
JWiggins*
Tech Ed*DATE 111/2/93 111/4/93 11/4/93 j 11/05/93 OFC C/OEAB:DORS
OGCB:DORS
C/OGCB:DORS
D/DORS NAME AChaffee Li PWen GMarcus BGrimes DATE PI 793 / /93 1 / /93 1//93[OFFICIAL
RECORD COPY]DOCUMENT NAME: G:\EJB1\MILLSTON.IN
IN 93-XX November xx, 1993 This information
notice requires no specific action or written response.
If you have any questions
about the information
in this notice, please contact the technical
contact listed below or the appropriate
Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. G me, Director Division f Operating
Reactor Support Office Nuclear Reactor Regulation
Technical
co act: Eric J. Benner, NRR (301) 504-1171 Attachment:
List cently Issued Information
Notices Resident Inspector (DAD) r lewe via E-mail on 10/22/93* See Previous Concurren OFC OEAB:DORS
SC/OEAB:DORS
- EMCB
- DE C/EMCB:DE NAME EBenner* odwin* G ornseth* JStrosnider*
1/2/93 10/19/93 11 93 11/4/93 I OFC EMEB:DE / C/EMEB:DE
D/DE PUB:ADM NAME GHammerj JNorberg*
JWi ins\ Tech Ed DATE 11129 [11/4/93 11/493 11/ 6193 OFC C/O :DORS OGCB:DORS
C/OGCB:DORS
D/DORS NAME AChaifee PWen GMarcus BGrimes DATE 11/ /93 11/ /93 11/ /93 I11/ /93[OFFICIAL
RECORD COPY]DOCUMENT NAME: G:\EJB1\MILLSTON.IN
I IN 93-XX November xx, 1993 This information
notice requires no specific action or written response.
If yoU have any questions
out the information
in this notice, please contact the technical
contact 1 sted below or the appropriate
Office of Nuclear Reactor Regulation (NRR roject manager.Brian K. imes, Director Division 1 Operating
Reactor Support Office Nuclear Reactor Regulation
Technical
contact: Eric J. enner, NRR (301) 50 -1171 Attachment:
List of Recently ssued C Information
Notices Resident Inspector (DAD) iewed via E-mail on 10/22/93* See Previous Concurre el OFC OEAB:DORS
/l SC/OEAB:DORS )EMCB:DE l C/EVd LI)NAME EBennerQ 'f , 1 EGoodwin*
I G'ornseth
J X'i JIt I DATE l 11/2/93 V / 10/19/93 l 2/93 OFC EMEB:DEitpv
D DD PUB:ADM NAME GHamm J% rberg ins Tech Ed DATE I/_/__93 _ _1 __93 114 3_/7 1 \OFC C/OEAB:DORS
OGCB:DORS
C OGCB:DDRS
D/DORS NAME AChaffee PWen GMarcus BGrimes DATE / /93 / /93 / /93___/_/93
[OFFICIAL
RECORD COPY]DOCUMENT NAME: G:\EJB1\MILLSTON.IN