Information Notice No. 88-94: Potentially Undersized Valve Actuators
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
December 2, 1988
Information Notice No. 88-94: POTENTIALLY UNDERSIZED VALVE ACTUATORS
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to potential
problems concerning valves that may be equipped with undersized actuators
incapable of providing sufficient thrust to seat, unseat or properly operate
valves during some design conditions. 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 do not constitute NRC requirements;
therefore, no specific action or written response is required.
Description of Circumstances:
In November 1987, the William B. McGuire Nuclear Station, Unit 1 (McGuire or
licensee), experienced problems with feedwater bypass control valve 1CF-107
for steam generator 1D. During the startup of the unit, the level on steam
generator 1D decreased to approximately 15 percent on the narrow range level
instrumentation when flow through valve 1CF-107 failed to increase as demanded
upon increase of reactor power to above 3 percent. During the licensee's
investi-gation, it was noticed that the valve was not responding as demanded
and that in some cases the valve stroke time was slower than required for the
control signal. Valve 1CF-107 is a Fisher Controls (Fisher) valve, Model
Number 667-ET, that was delivered to McGuire in 1975.
During subsequent investigations by the licensee and Fisher, it was determined
by Fisher that the actuator for valve 1CF-107 had been sized using a calcula-
tion that did not explicitly account for any valve packing friction forces.
The licensee identified additional valves supplied by Fisher and requested
that Fisher recalculate the actuator sizes to include allowances for valve
packing friction forces. These evaluations showed that although some valve
actuators were appropriately sized, some undersized actuators existed.
The licensee's immediate corrective actions for these undersized actuators
included spring adjustments wherever possible. In those cases in which com-
plete closure against design loads could not be assured, the valves were
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declared inoperable and were deactivated in their safe positions. Permanent
corrective actions being considered by the licensee include changing control
air operating limits, installing different springs, and installing larger
actuators. The licensee is also considering methods that could be used to
measure actual packing frictional forces for use during actuator resizing
calculations.
Discussion:
Fisher Controls contacted the NRC regarding the potential undersized actuator
issue, and an NRC inspection was subsequently conducted at Fisher to determine
the extent of the problem. On the basis of a review of Fisher documents and
discussions with Fisher personnel, the NRC determined that actuators for
valves supplied by Fisher may be undersized and incapable of seating,
unseating or properly operating their valves during some design conditions.
Fisher indicated that until the mid-1970s it had supplied sliding stem valves
with Fisher's standard single arrangement teflon packing, as its actuator
sizing technology was principally based on teflon packing. During the sizing
of actuators for teflon-packed valves, Fisher did not account for the teflon
packing friction forces as, based on their experience, the friction forces
were calculated to be small compared to the actuator air pressure forces,
actuator spring forces, valve differential pressure forces, and valve seating
forces. Around 1975, Fisher began supplying a number of valves with graphite
laminate packing as a result of nuclear power industry requests to eliminate
teflon material from radiation environments and general personal health and
safety concerns resulting in the replacement of asbestos packing material. In
April 1976, Fisher began to explicitly account for packing friction forces in
sizing all valve actuators when it became apparent that graphite packing
friction forces and other non-teflon packing materials contributed
significantly to the overall friction forces. The change was fully implemented
for all Fisher orders shipped after January 1, 1977.
During the NRC inspection, Fisher also stated that some nuclear power plant
licensees may have installed packing different from that provided in the
original valve. Such a change would be of concern if the new packing creates
higher friction forces than the original packing. For example, data provided
by Fisher indicates that increased friction forces can result if teflon
packing is replaced with graphite packing or graphite laminate packing is
replaced with graphite ribbon packing. If the size of the installed actuator
cannot overcome the increased friction forces associated with the packing
change, then the valve may be incapable of performing some of its intended
functions.
In addition, Fisher informed the NRC of the potential for undersized actuators
on Fisher 9200 series butterfly valves. These particular valves employ rotary
shafts rather than sliding stems and are not subject to the same packing
friction concerns previously discussed; however, some of these butterfly
valves may be equipped with undersized actuators for a different reason.
Fisher sized butterfly valve actuators ordered before March 1, 1982, using a
method that under some circumstances underestimated the torque required to
seat or unseat the butterfly disk in the 9200 series valves. Butterfly valves
ordered after
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December 2, 1988
Page 3 of 3
March 1, 1982, are not subject to this concern because they are equipped with
actuators sized by the current Fisher method that more accurately predicts
valve seat/disk frictional forces.
Conclusion:
The NRC has determined, on the basis of the McGuire event and the inspection
at Fisher Controls, that the following types of valves may be equipped with
undersized actuators that may not provide sufficient thrust to seat, unseat or
properly operate their valves during some design conditions:
1. Sliding stem valves supplied by any manufacturer that were repacked using
materials or procedures that increased the packing friction forces beyond
those accounted for in sizing the actuators.
2. Fisher Controls sliding stem valves shipped before January 1, 1977,
supplied with graphite and other non-teflon packing. The actuators for
these valves were sized by Fisher without accounting for packing friction
forces. Actuators for sliding stem valves supplied by other
manufacturers may also be undersized, depending on the actuator sizing
methods used by these manufacturers.
3. Fisher Controls 9200 series butterfly valves ordered before March 1,
1982. The method used to size the actuators for these valves may have
underestimated the torque needed to seat or unseat the butterfly disk.
Licensees who identify valves with potentially undersized actuators may wish
to contact the appropriate valve manufacturer to obtain additional
information.
No specific action or written response is required by this information notice.
If you have any questions regarding this matter, please contact one of the
technical contacts listed below or the Regional Administrator of the appropri-
ate regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Joseph J. Petrosino, NRR
(301) 492-0979
Jaime Guillen, NRR
(301) 492-1170
Attachment: List of Recently Issued NRC Information Notices
. Attachment
IN 88-94
December 2, 1988
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-93 Teletherapy Events 12/2/88 All NRC medical
licensees.
88-92 Potential for Spent Fuel 11/22/88 All holders of OLs
Pool Draindown or CPs for nuclear
power reactors.
88-91 Improper Administration 11/22/88 All holders of OLs
and Control of or CPs for nuclear
Psychological Tests power reactors and
all fuel cycle
facility licensees
who possess, use,
import, export, or
transport formula
quantities of
strategic special
nuclear material.
88-90 Unauthorized Removal of 11/22/88 All NRC licensees
Industrial Nuclear Gauges authorized to
possess, use,
manufacture, or
distribute
industrial nuclear
gauges.
88-89 Degradation of Kapton 11/21/88 All holders of OLs
Electrical Insulation or CPs for nuclear
power reactors.
88-88 Degradation of Westinghouse 11/16/88 All holders of OLs
ARD Relays or CPs for nuclear
power reactors.
88-87 Pump Wear and Foreign 11/16/88 All holders of OLs
Objects in Plant Piping or CPs for nuclear
Systems power reactors.
86-106, Feedwater Line Break 11/10/88 All holders of OLs
Supp. 3 or CPs for nuclear
power reactors.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
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