United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 84-66: Undetected Unavailability of the Turbine-Driven Auxiliary Feedwater Train

                                                          SSINS No.: 6835  
                                                          IN 84-66         

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                           WASHINGTON, D.C. 20555 

                              August 17, 1984 

Information Notice No. 84-66:   UNDETECTED UNAVAILABILITY OF THE TURBINE-
                                   DRIVEN AUXILIARY FEEDWATER TRAIN 

Addressees: 

All pressurized water power reactor facilities holding an operating license 
(OL) or construction permit (CP). 

Purpose: 

This information notice is provided to alert recipients of a potentially 
significant problem pertaining to undetected unavailability of the turbine-
driven auxiliary feedwater (AFW) train. It is expected that recipients will 
review the information for applicability to their facilities and consider 
actions, if appropriate, to preclude a similar problem occurring at their 
facilities. However, suggestions contained in this information notice do not
constitute NRC requirements and, therefore, no specific action or written 
response is required. 

Description: 

Sequoyah 2 

On January 12, 1982, the turbine-driven AFW pump at Sequoyah 2 failed to 
start on a safety injection actuation. Investigation revealed the electronic
overspeed trip latch function for the stop valve had not been relatched 
following an earlier overspeed trip. The valve is normally relatched from 
the control room. The operator had apparently not held the valve hand switch 
for the necessary 10 seconds, and there was a design deficiency in that no 
indication was provided in the control room to determine that the valve had 
been reset. As corrective actions, the licensee has modified procedures to 
require local visual verification of latching, improved valve checklists, 
and posted precautionary labels or signs both in the control room and 
locally at the stop valve. 

Salem 1 

On August 11, 1983, the turbine-driven AFW pump failed to start following a 
low-low steam generator level signal because the pump turbine trip valve was
in the tripped position. Although it could not be substantiated, the valve 
had apparently been tripped and left in that position following maintenance 
and testing activities on August 3, 1983. It appeared that when the pump was
removed from service, the control room "trip" pushbutton was inadvertently 
depressed instead of the "stop" pushbutton, resulting in activation of the 
trip valve. In addition, the valve trip position limit switch was out of 
adjustment causing the "trip" indication in the control room to be 
inoperable. A design 


8408100055 
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                                                         IN 84-66         
                                                         August 17, 1984  
                                                         Page 2 of 3      

change request was initiated to provide a positive control room indication 
of a trip valve latched condition.  Until this change is complete, the trip 
valve will be verified to be in the latched position by daily observation. 

Salem 2  

At approximately 1800 hours, October 5, 1983, during routine full power 
operation, the control room operator noticed that the trip indication light 
for the turbine-driven AFW pump was illuminated. Subsequent investigation 
revealed that the valve was in the tripped position and had apparently been 
left in that position following completion of routine pump surveillance 
testing at 1700 hours, October 5, 1983. When the problem was identified, the
AFW pump trip valve was latched. The redundant electrically driven pumps 
were operable throughout the occurrence and the turbine-driven pump was 
restored to operability within the time period specified in the action 
requirements. 

Investigation of the incident revealed that the operator who relatched the 
pump trip valve at the time of the surveillance had turned the valve 
handwheel to set the valve linkage but had not completed the latching 
operation by turning the handwheel back to the starting position. This 
resulted in the valve remaining in the tripped position. No local mechanical
position indication existed on the valve, thus detailed knowledge of the 
valve operating linkage was required to ensure that the valve was in the 
proper position. As a corrective action, the licensee installed local valve 
position indication, and the licensee is planning to install control room 
indication of the "latched" condition. 

San Onofre 3 

On October 31, 1983, at 1925 hours, Unit 3 was manually tripped from 62% 
reactor power in response to a loss of main feedwater. An emergency 
feedwater actuation signal (EFAS) was received when the unit was tripped. 
However, the turbine-driven AFW pump failed to start. Both electrically 
driven AFW pumps started and remained operable during this event. The 
operator investigated the failure of the turbine-driven pump, found the pump 
turbine in a tripped condition, and manually reset the pump turbine's steam 
admission valve. The cause of the pump trip was unknown. 

The pump had previously been satisfactorily tested on October 30, 1983, at 
1820 hours. Although control room instrumentation was available to signal 
when the pump turbine tripped on turbine overspeed, troubleshooting of the 
instrumentation subsequent to the plant trip on October 31, 1983, indicated 
that there were intermittent failures of the instrumentation to signal when 
the pump turbine was tripped. These intermittent failures were investigated 
and corrected. 

The San Onofre AFW pump turbine steam admission valve is normally closed and
opens when a EFAS signal is received. When the AFW pump turbine trips on 
overspeed, the condition is alarmed in the control room. However, it is 
possible to relatch the trip mechanism in such a way that the overspeed trip
is reset but the valve is not and the condition is not indicated in the 
control room. 
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                                                         IN 84-66       
                                                         August 17, 1984 
                                                         Page 3 of 3    

Ginna 

On December 28, 1983, with the reactor at 100% power, the plant entered a 
7-day Limiting Condition for Operation (LCO) Action Statement when it was 
discovered that the turbine driven AFW pump was inoperable. The cause was 
that the throttle on the pump had been tripped. The licensee felt that a 
contract person, working in the area of the pump, bumped the lever into the 
tripped position earlier in the day. The limit switch did not make contact; 
as a result, there was no indication in the control room of the pump being 
tripped. 

The valve was reset. The licensee investigation found that the valve 
operated sluggishly because of insulation debris in the external valve 
linkages. The valve limit switch had not been activated because of the 
limited valve stroke. 

Discussion: 

In five events at operating reactors (1982-1983), the turbine-driven AFW 
pumps were unavailable because the steam supply was isolated (trip and 
throttle valve was not latched). The condition was noted either during 
routine inspections or as the result of an investigation of failure of the 
turbine-driven AFW pump to respond to an engineered safety features 
actuation signal. Three of these five events were failures to return a 
safety system to an operable condition, including failure to verify, and 
maintenance was a significant contributing factor in four of the events. 

On the basis of AEOD evaluations, each of these events were found to have 
limited safety significance because (1) the motor-driven AFW pumps were 
operable and available in all cases, and (2) the LCO time period was 
generally not exceeded. However, because events involving undetected 
unavailability of the turbine-driven AFW train could be significant at other
plants or under other circumstances, the NRC recommends that recipients of 
this notice review these events and the various preventive actions 
summarized in Table 1 for applicability to their plants. 

No written response to this information notice is required. If you need 
additional information about 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:  Ray Smith, IE 
                    (301) 492-7190 

Attachments: 
1.   Table 1: Summary of Various Actions Taken by Facilities to Prevent
     Undetected Unavailability of the Turbine Driven AFW Train 
2.   List of Recently Issued IE Information Notices 
.

                                  TABLE 1 

        Summary of Various Actions Taken By Facilities to Prevent 
         Undetected Unavailability of the Turbine-driven AFW Pump 

1.   Design change to provide a positive control room indication of a trip 
     valve "latched" condition. 

2.   Regular adjustment and testing of the limit switches to ensure 
     operability (where limit switches are used to provide the control room 
     with the status of trip valves). 

3.   Local verification of position after resetting the trip valve. 

4.   Visual verification daily or once per shift to see that the valve is 
     not tripped. 

5.   Local mechanical valve position indication installed and permanent tags
     attached to the valve providing instructions for operation. 

6.   On-shift training in operation of the trip valve for all personnel who 
     are required to operate the valve. 

7.   Improved housekeeping to prevent fouling external valve linkages. 

8.   Warning sign installed near the trip lever. 

Page Last Reviewed/Updated Tuesday, November 12, 2013