Information Notice No. 86-61: Failure of Auxiliary Feedwater Manual Isolation Valve
SSINS No.: 6835
IN 86-61
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
July 28, 1986
Information Notice No. 86-61: FAILURE OF AUXILIARY FEEDWATER MANUAL
ISOLATION VALVE
Addressees:
All licensees of nuclear power plants and holders of construction permits.
Purpose:
This notice is provided to alert licensees to a failure of a manual
isolation valve as the result of a lack of maintenance on the valve during
the operational life of the plant.
It is suggested that recipients review this information for applicability
and consider actions, as appropriate, to preclude this and similar problems
from occurring at their facilities. However, suggestions contained in this
notice do not constitute NRC requirements; therefore, no specific action or
written response is required.
Description of Circumstances:
Following the loss of integrated control system (ICS) power at the Rancho
Seco plant on December 26, 1985, the plant tripped and an overcooling
transient occurred. Details of this event are documented in the NRC incident
investigation team's report, "Loss of Integrated Control System Power and
Overcooling Transient at Rancho Seco on December 26, 1985," NUREG-1195,
February 1986. When power was lost to the ICS, the plant responded as
designed; the auxiliary feedwater (AFW) ICS flow control valves, as well as
other valves, went to the 50-percent open position. The auxiliary feedwater
flow was excessive. When the local manual attempt to close the flow control
valve to the "A" once-through steam generator (OTSG) was unsuccessful, the
operator attempted to close the manual isolation valve. This isolation valve
could not be moved, even when a valve wrench was used.
The NRC incident investigation team (IIT) found that the failure of the
auxiliary feedwater manual isolation valve was the result of a lack of any
maintenance on this valve during the operational life of the plant, about
10-12 years. The lack of a preventive maintenance program resulted in the
valve being inadequately lubricated, which caused the valve to seize.
8607240026
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IN 86-61
July 28, 1986
Page 2 of 3
Discussion:
The AFW manual isolation valve is a locked-open valve located in the AFW
discharge header to the "A" OTSG. The licensee, Sacramento Municipal Utility
District (SMUD), considers that the entire AFW system, which would include
this manual isolation valve, is safety-related. However, it appears that
this valve was only intended to be used to isolate the AFW (ICS) flow
control valve for maintenance. The valve is a 6-inch, ANSI Class 900-lb,
pressure seal gate manufactured by Velan Engineering. It is categorized as
an ASME "Category E" valve (i.e., it is normally locked open to fulfill its
function). Section XI of the ASME Boiler and Pressure Vessel Code (1974
Edition) requires no regular testing of Category E valves. The positions of
the valves are merely recorded to verify that each valve is locked or sealed
in its correct position. The ASME Code no longer includes a Category E.
The Velan instruction manual provides the following guidance regarding
maintenance and operation of the valve:
o Lubrication of the stem threads and other working components should be
performed frequently and at least every 6 months. A lubrication
schedule recommends stem thread lubrication whenever the threads appear
dry and greasing of the yoke sleeve bearings concurrently with stem
thread lubrication.
o Valves that are not operated frequently and may remain open or closed
for long periods of time should be worked, even if only partially,
about once a month.
o Proper lubrication of the stem and sleeve can reduce required operating
torque by 7 to 30 percent.
o A caution also is provided not to use valve wrenches on the handwheels.
A review of the maintenance history of the "A" manual isolation valve
indicated that no maintenance (preventive or corrective) had been performed
on the valve during the operational life of the plant (i.e., since 1974).
The licensee had no program for preventive maintenance of manual isolation
valves in the plant.
Two similar valves had failed previously, which prevented movement of the
valve from the open position. The discharge isolation valve from the "A" AFW
pump failed on November 20, 1979 and the AFW manual isolation valve to the
"B" OTSG failed on February 20, 1980. In both cases, the yoke bearings were
found seized and had to be replaced.
During the December 26, 1985 incident, it was necessary to isolate AFW flow
to the OTSG to terminate the overcooling. When the flow control valve could
not be closed, the operator tried to close the manual isolation valve.
Because of the lack of maintenance, the isolation valve could not be closed
when it was needed. To address this problem, the SMUD has identified about
100 manual isolation valves with functions similar to the AFW manual
isolation valve, that will now be included in their preventive maintenance
program.
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IN 86-61
July 28, 1986
Page 3 of 3
Additional discussion on the AFW manual isolation valve is included in
Section 5.3 of NUREG-1195.
No specific action or written response is required by this information
notice. 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: R. Wright, NRR
(301) 492-8900
H. Bailey, IE
(301) 492-9006
Attachments: List of Recently Issued IE Information Notices
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