Information Notice No. 88-59: Main Steam Isolation Valve Guide Rail Failure at Waterford Unit 3
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
August 9, 1988
Information Notice No. 88-59: MAIN STEAM ISOLATION VALVE GUIDE RAIL
FAILURE AT WATERFORD UNIT 3
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice discusses a main steam isolation valve (MSIV) guide
rail failure at Waterford 3 and its possible generic implications. The MSIV
is a D-2 Power Seal type, manufactured by ACF Industries, WKM Valve Division.
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:
On April 11, 1988, during a routine inspection at Waterford 3, MSIV debris was
found in the strainer for the main turbine throttle valve. The disassembly
and inspection of the two MSIVs at the plant revealed that the downstream
guide rails in one of the valves (see attached drawing) had become completely
dislodged, and several bolt heads on the still-attached upstream rails in the
same valve had been completely severed. The other MSIV had several separated
bolt heads on both upstream and downstream rails, but the guide rails were in
place. There were also galling marks on the chamfer of the guide rail and on
the shoe attached to the lever lock arm.
Discussion:
An analysis by the licensee indicates that the guide rail failure was caused
by the force of the lever lock arm assembly contacting the rail. The valve,
however, passed the inservice test requirements. The analysis concludes that
even without the rails the valve could still perform its function, albeit at a
closure time that is slower by about a second, under the worst-case condition.
However, there is a possibility that a detached rail could jam the MSIV in a
partially open position. The failure of one MSIV is accounted for in the
utility's Safety Analysis Report.
8808030112
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IN 88-59
August 9, 1988
Page 2 of 2
After the failure at Waterford 3, a fiberscope examination of the WKM power
seal MSIVs at San Onofre Unit 3 revealed a broken bolt lying in the bottom
section of the body of one MSIV. Disassembly and inspection of this valve
revealed three failed bolts, galling marks on the shoe and the chamfer, and an
upstream rail slightly detached from the skirt plate. At the same plant, a
shutdown cooling isolation valve of a similar design was also damaged. How-
ever, the licensee believes that this damage occurred during maintenance. The
damage was similar to that found on the MSIVs, that is, galling marks, failed
bolts, and detached rails, but, in addition, the skirt plate was fractured and
the shoe was wedged into the lever arm pivot slot.
The NRC believes this type of failure could be generic to other plants.
Valves of this type are also reported to be in use at San Onofre 2, South
Texas 1 and 2, and Washington Nuclear Power Unit 2. Valves of similar design
could exist at other plants. The preliminary indications suggest that the
failures are attributable to deficiencies in fabrication, engineering, and
materials. The corrective actions considered at Waterford and San Onofre 3
include
(1) stelliting the shoes and the chamfer on the rails
(2) verifying the bolt alignments
(3) doing nondestructive examinations of all new bolts
(4) changing the angles of the rails and of the shoes
(5) increasing the valve closure time (within system performance
constraints)
(6) periodically making fiberscope examinations of the valve internals
to detect excessive galling, severed guide rail bolts, and separated
guide rails
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: Kenneth Dempsey, NRR
(301) 492-0918
Attachments:
1. Figure of Valve
2. List of Recently Issued NRC Information Notices
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