United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-61: Failure of Auxiliary Feedwater Manual Isolation Valve

                                                            SSINS No.: 6835 
                                                            IN 86-61       

                                UNITED STATES
                           WASHINGTON, D.C. 20555

                                July 28, 1986

                                   ISOLATION VALVE 


All licensees of nuclear power plants and holders of construction permits. 


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. 


                                                              IN 86-61     
                                                              July 28, 1986 
                                                              Page 2 of 3  


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 

                                                              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 

                                   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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