Information Notice No. 88-59: Main Steam Isolation Valve Guide Rail Failure at Waterford Unit 3

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                 August 9, 1988

                                   FAILURE AT WATERFORD UNIT 3


All holders of operating licenses or construction permits for nuclear power 


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. 


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.  


                                                         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 

     (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 

     (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

                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contact:  Kenneth Dempsey, NRR 
                    (301) 492-0918

1.  Figure of Valve
2.  List of Recently Issued NRC Information Notices

Page Last Reviewed/Updated Friday, May 22, 2015