United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-14: PWR Auxiliary Feedwater Pump Turbine Control Problems

                                                            SSINS No: 6835 
                                                            IN 86-14       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                            WASHINGTON, DC 20555

                               March 10, 1986

Information Notice No. NO 86-14:   PWR AUXILIARY FEEDWATER PUMP TURBINE 
                                   CONTROL PROBLEMS 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP) 

Purpose: 

This information is provided to alert recipients of potential problems of 
overspeed trips of turbine-driven auxiliary feedwater (AFW) pumps which 
contribute to systems unavailability Similar overspeed trips are employed 
on turbine-driven high pressure injection pumps and reactor core isolation 
cooling pumps 

It is expected that recipients will review the information in this notice 
for applicability to their facilities and consider actions, if appropriate, 
to preclude similar problems occurring at their facilities However, 
suggestions contained in this information notice do not constitute NRC 
requirements; therefore, no specific action or written response is required

Description of Circumstances: 

There have been four relatively recent events during which the 
turbine-driven AFW pumps tripped as a result of overspeed to a "lockout" 
condition that required manual reset at the turbine to return the component 
to an operable status In two events, the cause was the presence of oil 
pressure in the turbine governor before receipt of an initiating signal 
These events occurred at Turkey Point and Crystal River In the other two 
events, the overspeed trip was attributed to condensate in the feedwater 
turbine steam lines These events occurred at Davis-Besse and Palo Verde 

The events cited are examples of system malfunctions where individual 
components responded as designed However, the system was unable to perform 
its intended function because overall system dynamic problems were not fully
considered 

At Turkey Point all three AFW turbines responded properly when called on 
after a reactor trip When later required to restart, two of the AFW 
turbines tripped to lockout on overspeed and the third turbine tripped (from 
a different device) on overspeed 



8603050391 


                                                             IN 86-14      
                                                             March 10, 1986 
                                                             Page 2 of 4   

At Crystal River, the AFW turbine tripped on overspeed during performance of
a routine operability test 

At Davis-Besse one of two turbine-driven main feedwater pumps tripped while 
the unit was operating at 90 percent power Steam to the second main 
feedwater pump turbine was lost when the main steam isolation valves 
spuriously closed After the resultant reactor trip, the turbine-driven AFW 
pumps started on demand, but tripped on overspeed Various other problems 
developed, which are discussed in Information Notice No. 85-50, IE Bulletin 
85-03, and in greater detail in NUREG-1154 

At Palo Verde, the AFW turbine tripped on overspeed during a startup test 

In each of these instances an operator was required to go to the turbines 
and manually reset the equipment for restart These events were similar in 
consequences, but had different underlying causes 

Discussion: 

Historically, PWRs have been required to have redundant AFW systems to 
remove residual reactor decay heat after scram Normally, at least one of 
the systems has been powered by other than an electric motor, to address the
contingency of loss of all ac power Nearly all current PWR licensees have a 
small steam turbine drive, most of which are Terry Corporation single-stage 
noncondensing turbines with Woodward governors Woodward governors used with
Terry turbines do not have an internal overspeed trip device The turbine 
has a mechanical overspeed trip that will trip the "trip-and-throttle" valve 
at 150 percent of nominal speed Terry Corporation recommends visual 
post-trip examination of the equipment, following mechanical overspeed trip 
and has the trip linkage arranged to require local manual reset at the 
turbine Many turbines are equipped with additional speed sensing devices 
that can be used to trip the turbine at some lower overspeed, eg, 125 
percent 

Woodward mechanical-hydraulic governors sense the speed of the turbine 
through gearing that rotates the mechanical fly weights and provides power 
to supply hydraulic oil to the governor The governor acceleration control 
feature is set to function properly on a start signal when the turbine 
starts from a dead stop with no initial oil pressure in the governor control 
system 

Control oil pressure does not decay immediately when a governor is shut 
down Depending on internal clearances, it may take as long as 30 minutes to 
fully decay Some facilities utilize power-operated auxiliary devices to 
provide for remote control of governor speed setting and to "dump" residual 
oil from the hydraulic system However, the most commonly used device seems 
to be a speed setting knob that must be adjusted manually at the governor 
This requires that the governor speed be turned down to a minimum to dump 
the excess oil and then reset to the desired speed This action introduces 
two possibilities for human error: the operator may inadvertently not fully 
dump the hydraulic system or may not correctly reset the speed control 


                                                             IN 86-14      
                                                             March 10, 1986 
                                                             Page 3 of 4   

Details of Recent Events: 

At Turkey Point all three pumps started properly on the first demand During
recovery from the event, the pumps were no longer needed and were shut down
The turbine governors were reset per procedure, but as discussed above, 
perhaps not properly reset During the continuing course of the plant 
transient, the AFW systems received another auto-start signal Two of the 
turbines experienced overspeed and tripped to lockout The third 
turbine-driven pump had experienced problems with a feedwater discharge flow
control valve, and the steam supply valves had been placed in an unusual 
configuration to facilitate troubleshooting on the water flow control valve
The turbine started automatically, but somewhat more slowly than normal It 
experienced overspeed, as did the others, but in this case the acceleration 
rate was slow enough that the electric overspeed device activated and 
tripped the "trip-and-throttle" valve Immediately on closure the trip 
signal cleared and a reset signal was generated The turbine governor had 
not been reset, and as the valve opened, the turbine restarted, went to 
overspeed, was intercepted and shut down by the electric device, and 
continued this cycling until manually secured The initial corrective action 
was to clarify the governor reset procedure and to retrain the operators 
Since then the licensee has engaged in a major system design review and 
upgrade 

At Crystal River, the single turbine drive had apparently been properly shut
down, but during the interval between test operations, the steam supply 
valve had developed a slight leak, enough so that the turbine was "idling" 
at about 160 rpm, a speed sufficient to activate the governor hydraulic 
system When the start signal was initiated, the turbine accelerated rapidly 
and tripped to lockout on overspeed The licensee corrective action was to 
overhaul the steam supply valve so that it no longer leaked 

At Davis-Besse, the licensee reports that the turbine overspeed events were 
caused by the presence of undrained condensation in the steam supply lines 
The particular lines being used at the time of the overspeed events were 
used only following certain accident sequences and were not normally 
pressurized and heated These lines have long horizontal runs in which large 
quantities of condensate could collect When the AFW start signal caused the 
steam supply valves to open, much of the steam initially introduced was 
condensed by the cold pipe and then swept into the turbines This water, 
containing significantly less energy than an equivalent mass of steam, 
caused the turbines to accelerate slowly and the governors to open the 
control valves farther than normal When the condensate cleared the turbines 
and was replaced by steam, the governors could not react rapidly enough to 
prevent the turbines from overspeeding and locking out The auxiliary 
feedwater system had not been tested in this configuration before the 
overspeed events The initial corrective action during the transient was to 
control the AFW turbines by local manual control Currently the system is 
undergoing extensive design review and revision 

At Palo Verde, the licensee reports that, like Davis-Besse, the overspeed 
trip also occurred because of condensation in the steam supply line The 
circumstances differ, however, in detail As at Davis-Besse, the branch 
connection from the main steam supply lines was fairly long, but was 
intended to be 


                                                             IN 86-14      
                                                             March 10, 1986 
                                                             Page 4 of 4   

pressurized to the turbine stop valve whenever steam was available Traps 
and drain connections were provided to ensure that any condensation was 
continuously removed However, these devices had not been verified to be 
functional and properly adjusted, and in fact, significant quantities of 
condensate were injected into the AFW turbine on startup Corrective action 
was to verify that installed condensate removal devices functioned according
to design, and that procedures required periodic verification of 
operability 

All of the above-described events resulted in unavailability of the AFW 
system requiring operator action to restore system operability The 
underlying causes include inappropriate system design, poor operating 
procedures, and inadequate maintenance 

No specific action or written response is required by this information 
notice If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or the Technical 
Contact listed in this notice 


                                   Edward L Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  James B Henderson, IE
                    (301) 492-9654 

Attachment: List of Recently Issued IE Information Notices 

Page Last Reviewed/Updated Tuesday, November 12, 2013