Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
September 24, 1997
NRC INFORMATION NOTICE 97-74: INADEQUATE OVERSIGHT OF CONTRACTORS DURING
SEALANT INJECTION ACTIVITIES
Addressees
All holders of operating licenses for nuclear power reactors except those who
have permanently ceased operations and have certified that fuel has been
permanently removed from the reactor vessel.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to the consequences of inadequate oversight of
contractors during sealant injection activities. It is expected that
recipients will review the information for applicability to their facilities
and consider actions, as appropriate, to avoid similar problems. Suggestions
contained in this information notice are not NRC requirements; therefore, no
specific action or written response is required.
Description of Circumstances
Beaver Valley
The head vent system (HVS) at Beaver Valley Unit 2 removes noncondensable
gases from the reactor vessel head and is designed to mitigate the
consequences of inadequate core cooling or impaired natural circulation
resulting from the accumulation of noncondensable gases in the reactor coolant
system (RCS).
In November 1996, with Unit 2 in Mode 5 (cold shutdown) near the end of an
extended refueling outage, operators noted a leak at a blind flange downstream
of a normally shut 1-inch flow-gauge isolation valve located in a dead-leg
portion of the HVS. The leak measured approximately 15 drops per minute. On
December 2, 1996, sealant was injected into an upstream valve to temporarily
stop the leakage. Following the sealant injection, the reactor was restarted
on December 3, 1996. Subsequently, as a result of concerns raised by the NRC
regarding the leaktightness of several valves upstream of the valve where
sealant was injected, Unit 2 was shut down and the valves were tested for
leaks. During this post-maintenance testing, it was discovered that some
sealant had migrated to other portions of the HVS, clogging two HVS flow
control valves and causing one of these valves to become bound and unable to
fully stroke.
9709180079. IN 97-74
September 24, 1997
Page 2 of 4
As a result of this event, the plant manager issued a stop-work order and also
ordered (1) a review of the leak repair process at the plant, (2) a check of
all existing leak repairs, and (3) a review of vendor oversight practices.
Several factors contributed to the event at Beaver Valley Unit 2:
(1) Licensee engineering provided improper information to the vendor
performing the repair. Engineering specified normal RCS operating
pressure and temperature conditions (610�F and 2235 psia) to the vendor
instead of the actual conditions under which the repair would be made
(close to ambient). As a result, the wrong sealant material was used.
(2) The licensee did not review vendor procedures adequately and did not
exercise sufficient monitoring and control of vendor activities.
Specifically, there was no monitoring of the quantity of sealant
injected, the injection pressure of the sealant, or the location of the
injection port.
(3) Significant weaknesses were found in work instructions, quality
assurance and quality control involvement, sealant material selection,
injection port location, and direct vendor oversight. Work
instructions, prebriefings, and overall vendor oversight were
inadequate.
As a result of inadequate licensee control of the injection of sealant
material into the HVS at Unit 2, twice as much sealant was injected into the
valve as was specified in the maintenance work package. The sealant failed to
harden properly, migrated to unintended portions of the HVS, and degraded the
HVS flow control valves when it accumulated on the valve seats. One of the
valves became bound and was unable to fully stroke. Because the valves were
inoperable, the HVS would not have been able to perform its gas-removal
function".
LaSalle
On June 19, 1996, with both units operating at 100 percent power, nonessential
service water (SW) system discharge pressures began to decrease because of the
high differential pressures across the in-line strainers. The operators
backwashed the strainers, restoring the normal discharge pressures. On June
24, 1996, the problem recurred, causing high temperature in a diesel fire pump
during routine surveillance testing.
The licensee's root cause determination following the initial event focused on
material generated from sandblasting performed on the exterior of the lake
screenhouse. The licensee initially believed that some of the sandblasting
material had become entrained in the . IN 97-74
September 24, 1997
Page 3 of 4
SW, fouling the strainers. After the June 24 event, the licensee determined
that both events had been caused by the injectable sealant that had been used
to repair cracks in the floor of the service water building, which is also the
roof of the SW intake tunnel. The tunnel provides a common water source for
both the SW and emergency service water (ESW) systems of Unit 1 and Unit 2.
As a result of the crack repair activities, a large amount of sealant entered
the tunnel and a portion of it was drawn into the SW strainers.
Following the June 19 and June 24 events, the licensee erroneously concluded
that the material that fouled the SW system strainers could not affect the ESW
systems. On June 28, 1996, during operations to clean the SW intake tunnel,
divers found sealant in the tunnel in a place that could compromise the
operability of the ESW systems. Subsequently, the licensee declared the ESW
system inoperable and shut down both reactors.
An Augmented Inspection Team (AIT) was sent to the site to investigate the
sealant injection event. It concluded that the root cause of the strainer
fouling was poor control of work on a safety-related structure. The licensee
staff responsible for assigning and controlling this work did not know enough
about the facility to appreciate the potential consequences of this work.
Therefore, a contractor, who was permitted to seal cracks in the safety-
related SW intake tunnel structure, had no knowledge of the potential impact
of the work, no approved procedures, and inadequate licensee oversight. The
AIT also concluded that an inadequate assessment of the root cause of the
June 19 and June 24 events, as well as the failure to develop an initial
inspection and recovery plan that was comprehensive and thorough, permitted
repeated challenges to key safety systems and threatened the availability of
the ultimate heat sink (UHS). Loss of the function of these safety systems,
and the resultant loss of the UHS, would have significantly affected the
licensee's ability to respond to analyzed accidents. Had the root cause for
the initial event been thoroughly evaluated, the event of June 24 could have
been avoided, reducing the time that the ESW system for both units was
threatened.
Conclusion
These events illustrate the consequences and the possible safety impact of
inadequate oversight of contractors during sealant injection activities. Such
activities can adversely impact on the ability of safety-related systems to
perform their intended safety function if called upon.
Related Generic Communications
U.S. Nuclear Regulatory Commission, Information Notice (IN) 82-06, "Failure of
Steam Generator Primary Side Manway Closure Studs," dated March 12, 1982.
U.S. Nuclear Regulatory Commission, IN 85-90, "Use of Sealing Compounds in an
Operating System," dated November 19, 1985.
U.S. Nuclear Regulatory Commission, IN 93-90, "Unisolatable Reactor Coolant
System Leak Following Repeated Applications of Leak Sealant," dated
December 1, 1993.. IN 97-74
September 24, 1997
Page 4 of 4
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.
signed by D.B. Matthews for
Jack W. Roe, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: William F. Burton, NRR
301-415-2853
E-mail: [email protected]
T. Jerrell Carter, Jr.
301-415-1153
E-mail: [email protected]
Attachment: List of Recently Issued NRC Information Notices
