United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-09: Reduced Reliability of Steam-Driven Auxiliary Feedwater Pumps Caused by Instability of Woodward PG-PL Type Governors

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                                 March 18, 1988


Information Notice No. 88-09:  REDUCED RELIABILITY OF STEAM-DRIVEN 
                                   AUXILIARY FEEDWATER PUMPS CAUSED BY 
                                   INSTABILITY OF WOODWARD PG-PL TYPE 
                                   GOVERNORS


Addressees: 

All holders of operating licenses or construction permits for nuclear power 
reactors. 

Purpose: 

This information notice is provided to alert addressees to continuing problems 
affecting the reliability of steam-driven auxiliary feedwater pumps caused by 
instability problems with Woodward governors.  It is expected that recipi-
ents will review the information for applicability to their facilities and 
consider actions, if appropriate, to avoid similar problems.  However, sugges-
tions contained in this information notice do not constitute NRC requirements; 
therefore, no specific action or written response is required. 

Description of Circumstances: 

The steam-driven auxiliary feedwater pumps at Calvert Cliffs are powered by 
Terry steam turbines (GS-2N) with Woodward PG-PL type governors.  Before 
July 23, 1987, periodic surveillance testing of the steam-driven auxiliary 
feedwater pumps (AFWPs) was preceded by a warmup of the turbines before 
initiation of the quick startup tests.  On July 23, 1987, during a loss-
of-offsite-power event, the number 11 AFWP on Unit 1 tripped on its initial 
demand as a result of turbine overspeed.  To ensure that future periodic 
(monthly) surveillance testing of the turbine-driven AFWPs would be conducted 
under more realistic conditions, the test procedures were modified to require 
quick starts from cold conditions.  During subsequent tests in July through 
October 1987, a number of trips of the steam-driven AFWPs occurred at Calvert 
Cliffs.  On July 30, 1987, during rapid cold startup testing, both of the Unit 
2 steam-driven pumps tripped.  On September 26, 1987, the number 11 AFWP on 
Unit 1 began oscillating after the initial startup attempt and subsequently 
tripped on overspeed.  On October 23, 1987, the number 12 AFWP on Unit 1 
tripped on overspeed. 

The licensee conducted an intensive testing and troubleshooting program to 
determine the causes of the failures.  During these tests, a number of test 




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failures were experienced because of turbine governor oscillation and 
overspeed.  The most frequent failure sequences were either rapid initial 
acceleration of the turbine to the overspeed trip point, or large undamped 
speed oscillations that increased in magnitude to the overspeed trip point.  
Less frequently, trips occurred when the mechanical latch mechanism holding 
the trip valve open (which appeared to be overly sensitive) tripped.  
Subsequent attempts to test the pumps immediately after initial steam-driven 
AFWP failures were normally successful.

Discussion: 

Several factors were identified which appear to have contributed to the 
reduced reliability of the AFWPs.  These include: 

1.   Use of governor buffer springs of less than optimal stiffness, resulting 
     in the inability of the governor to dampen out upset conditions.  One of 
     the installed governors and all three of the spare governors had buffer 
     springs of a lower stiffness than that listed in the procurement specifi-
     cation on file at the Woodward company.  

2.   Excessive condensate trapped in the steam supply lines, resulting in 
     governor valve damage, governor linkage damage, and throttle control 
     instabilities as slugs of water hit the governor valve and turbine wheel.

3.   Improperly adjusted and degraded governor linkage, resulting in excessive 
     linkage play.

4.   Governor valve binding, resulting in governor actuator over-reaction to 
     small feedback signals.

5.   A failed governor on the Unit 2, number 22 AFWP.

6.   Damaged and misaligned overspeed trip mechanisms, resulting in 
     oversensitivity to vibration, jarring, and waterhammer.

The licensee implemented several corrective actions and plans additional 
upgrades.  These are described below. 

1.   Stiffer buffer springs were installed in the governors of all AFWPs to 
     increase control system dampening at the expense of increased control 
     system response time.

2.   Upgrading of both the procedures and the systems was initiated, which 
     included more thorough drain procedures and drain lineup verification.  
     The interval for manually draining the steamlines and turbine casings was 
     decreased from every 8 to every 4 hours.  Additional manual drains were 
     installed in the system low points to eliminate water from the 
     steamlines.  
     
3.   Various parts of the governor valves, governor linkages, and trip 
     linkages were overhauled, adjusted, and replaced.  Trip linkages 
     associated with 
     
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                                                            Page 3 of 3 


     the overspeed mechanisms and the trip throttle valves were adjusted to 
     increase trip latch engagement and thereby reduce sensitivity to physical 
     shock.  For some parts, such as linkage plates (cams), it was necessary 
     for the utility to obtain the special materials involved and fabricate 
     replacement parts in house. 
     
4.   Further steamline drain improvements are being evaluated.

The Calvert Cliffs problems highlight the importance of optimally sizing 
buffer springs, since the single, most effective short-term corrective action 
appeared to be installation of the stiffer buffer springs.  However, changes 
in spring stiffness for the purpose of improving stability can adversely 
affect other governor response characteristics.  Therefore, the selection of 
optimal spring stiffness should be carefully considered.  In addition, it is 
important to ensure maintenance of proper spring stiffness following initial 
determination of optimal stiffness.  In the case of Calvert Cliffs, the 
addition of stiffer springs appeared to provide an extra margin of stability.  
This temporarily compensated for other auxiliary feedwater system deficiencies 
that also required correction. 

Reliability problems were much more evident when the auxiliary feedwater pumps 
were periodically tested using quick starts from cold conditions.  This demon-
strates the importance of surveillance testing which, in so far as practical, 
duplicates the service conditions that would exist if the equipment were 
called on to operate.

Information Notice 86-14, "PWR Auxiliary Feedwater Pump Turbine Control Prob-
lems," and 86-14, Supplement 1, "Overspeed Trips of AFW, HPCI, and RCIC Tur-
bines," discuss problems closely related to those discussed in this 
information notice.  

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 NRC 
regional office. 




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

Technical Contact:  D. Limroth, RI
                    (215) 337-5121

Attachment:  List of Recently Issued NRC Information Notices
.                                                            Attachment
                                                            IN 88-09
                                                            March 18, 1988
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                            NRC INFORMATION NOTICES 
_____________________________________________________________________________
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-08          Chemical Reactions with       3/14/88        All NRC licensees 
               Radioactive Waste                            generating or pro-
               Solidification Agents                        cessing low level 
                                                            radioactive waste.

88-07          Inadvertent Transfer of       3/7/88         All NRC broad 
               Licensed Material to                         licensees and 
               Uncontrolled Locations                       licensees 
                                                            authorized to 
                                                            possess byproduct 
                                                            material as sealed
                                                            sources in 
                                                            teletherapy units 
                                                            or "self-
                                                            contained" 
                                                            irradiators. 

88-06          Foreign Objects in Steam      2/29/88        All holders of OLs
               Generators                                   or CPs for PWRs. 

88-05          Fire in Annunciator Control   2/11/88        All holders of OLs
               Cabinets                                     or CPs for nuclear
                                                            power reactors. 

88-04          Inadequate Qualification      2/5/88         All holders of OLs
               and Documentation of Fire                    or CPs for nuclear
               Barrier Penetration Seals                    power reactors. 

88-03          Cracks in Shroud Support      2/2/88         All holders of OLs
               Access Hole Cover Welds                      or CPs for BWRs. 

88-02          Lost or Stolen Gauges         2/2/88         All NRC licensees 
                                                            authorized to 
                                                            possess gauges 
                                                            under a specific 
                                                            or general 
                                                            license. 

88-01          Safety Injection Pipe         1/27/88        All holders of OLs
               Failure                                      or CPs for nuclear
                                                            power reactors. 

86-81,         Broken External Closure       1/11/88        All holders of OLs
Supp. 1        Springs on Atwood & Morrill                  or CPs for nuclear
               Main Steam Isolation Valves                  power reactors. 
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit 
Page Last Reviewed/Updated Tuesday, November 12, 2013