Information Notice No. 83-70: Vibration-Induced Valve Failures
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
October 25, 1983
Information Notice No. 83-70: VIBRATION-INDUCED VALVE FAILURES
All nuclear reactor facilities holding an operating license (OL) or
construction permit (CP).
This information notice is provided as a notification of events that
resulted in valve failures and system inoperability as a result of normal
operational vibration. It is expected that recipients will review the
information for applicability to their facilities. No specific action or
response is required at this time.
Description of Circumstances:
A review of recent Construction Deficiency Reports and License Event Reports
indicates that there have been a number of vibration-induced valve failures.
Discussions with General Electric indicate that some of these failures may
be generic to a specific valve type. The following is a brief account of
some of these events.
On October 22, 1982, at Quad Cities Station Unit 2, it was decided to cycle
the 2A recirculation pump discharge valve during the current maintenance
outage. The valve had exhibited problems in opening and closing in the past
and the licensee wanted to verify proper operation while the reactor was
shut down. When the valve was given a close signal, it would not fully
close. An inspection of the valve in the Unit 2 drywell revealed that two of
the four valve yoke-to-bonnet holddown studs and nuts were missing and the
valve motor operator had pulled the yoke away from the valve. Further
investigation revealed that the valve stem was bent and would have to be
replaced. Apparently the valve studs and nuts had loosened and fallen out
from normal system vibration.
On June 21, 1983, at Quad Cities Station Unit 1, the maintenance department
was investigating a position indication problem on a suppression pool return
valve in the B loop of the residual heat removal (RHR) system. An inspection
of the valve revealed that two of the four bolts that hold the valve yoke to
the bonnet had vibrated loose. This allowed the yoke to separate from the
bonnet causing the valve stem to bind excessively and finally bend. The B
loop of the RHR containment cooling system was declared inoperable until the
valve could be manually opened.
October 25, 1983
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On January 14, 1983, at Browns Ferry Station Unit 3, during routine testing
of the RHR valves, a low pressure coolant injection (LPCI) valve failed to
operate properly. An inspection of the valve revealed that the stud and nut
combination that retains the yoke collar device had loosened. This allowed
the motor operator to turn (with the yoke) around the valve stem causing
motor and valve damage. An inspection of other RHR and LPCI valves
indicated, that 50% of these valves had loose collar devices. The loosened
devices were attributed to vibrational loading of the yoke-to-bonnet
interface. The affected valves are gate valves manufactured by the Walworth
Company. Locking devices were installed on the studs and nuts of the collar
device to prevent future instances of vibrational loosening.
At Shoreham Station Unit 1, during valve testing, it was discovered that a
stem clamp was missing on an RHR globe valve. Although this was considered
an isolated event, the appropriate startup procedure was revised to include
a check to ensure that each stem clamp was properly oriented on the stem,
with the clamp key and setscrew properly tightened. Following this event,
another globe valve failed to stroke while being tested. The valve stem
clamp setscrew loosened, allowing the clamp to slide along the stem and the
clamp key to fall from its keyway. This allowed the motor operator to rotate
the stem without moving the valve disc. It is believed that the setscrew in
the stem clamp loosened because of normal system vibration. Stone & Webster
performed a review of the safety-related valves at Shoreham and has
determined that only globe valves manufactured by the Anchor Darling Co. are
susceptible to vibrational failures of this type.
Following these events at Shoreham Station, General Electric notified the
NRC that similar failures of this type were experienced in the high pressure
core spray (HPCS) system at Zimmer Station. The valves were Anchor Darling
globe valves specified by General Electric for HPCS systems in the test
return line of all BWR/5s and BWR/6s. To preclude the possibility of future
failures, both Anchor Darling and General Electric have provided
recommendations on how to secure the stem clamp setscrews.
The valve failure at Shoreham Station was especially significant because the
remote valve position indication was from limit switches on the motor
operator, so the valve appeared to be opening and closing normally when in
fact the valve had not moved. Station personnel should be aware of the
potential for vibrational loosening of valve components and may want to
emphasize this aspect in valve preventive maintenance.
Other recently issued IE generic communications addressing valve locking
devices include, Information Notice No. 81-33, "Locking Devices
Inadequately Installed on Main Steam Isolation Valves," IE Circular No.
80-04, "Securing of Threaded Locking Devices on Safety-Related Equipment,"
and IE Circular No. 79-04 "Loose Locking Nut on Limitorque Valve Operators."
October 25, 1983
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No written response to this notice is required. If you have any questions
regarding this matter, please contact the Regional Administrator of the
appropriate NRC Regional Office, or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Paul R. Farron
List of Recently Issued IE Information Notices
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