United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-14, Supplement 1: Overspeed Trips of AFW, HPCI, and RCIC Turbines

                                                     SSINS No: 6835       
                                                     IN 86-14, Supplement 1 

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

                              December 17, 1986

Information Notice No. NO 86-14, SUPPLEMENT 1:    OVERSPEED TRIPS OF AFW, 
                                                  HPCI, AND RCIC TURBINES 

Addressees: 

All nuclear power reactor facilities holding an operating license or a 
construction permit 

Purpose: 

This notice provides information that supplements that contained in 
Information Notice 86-14 regarding overspeed trips of Auxiliary Feedwater 
(AFW) turbines 

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

Background: 

Information Notice No. 86-14 described four events at PWRs during which 
turbine-driven AFW pumps tripped requiring manual reset Additional review 
has identified similar failures at other PWR facilities and BWR facilities 

The NRC Office of Analysis and Evaluation of Operating Data (AEOD) has 
issued a study of existing data (from Licensee Event Reports) entitled 
"Operational Experience Involving Turbine Overspeed Trips," AEOD/C602 This 
information notice provides a summary of that study* 

Description of Circumstances: 

The AEOD study examined a large population of events and focused on 
overspeed trips of turbine drives for AFW system service on PWRs and similar 
turbine drives for BWRs in high-pressure coolant injection (HPCI) and 
reactor core isolation cooling (RCIC) service Essentially all the above 
turbines are supplied by the Terry Corporation (Terry) and are equipped with 
governors made by the Woodward Governor Company (Woodward) 

*A copy of the study report is available in the NRC Public Document Room, 
1717 H Street N W, Washington, DC, 20555 for inspection and copying 


8612120139 


                                                     IN 86-14, Supplement 1 
                                                     December 17, 1986     
                                                     Page 2 of 3           

The study concludes that the dominant attributed causes of turbine overspeed
trips are governor speed control problems and problems with the trip valve 
and overspeed trip mechanism 

The governor speed control problems involve the following: 

1   Slow response of the governor during quick startup 

     Turbine overspeed trips at Zion 1 and LaSalle 1 were attributed to 
     governor valve binding while closing This condition occurred on 
     turbines equipped with Model PG and EG Woodward governors, 
     respectively 

     Incidents at Arkansas 2, Susquehanna 1, Palo Verde 1, and Grand Gulf 
     were related to the sensitivity of the Model EG governor speed control 
     characteristic function to minor system deficiencies, which by 
     themselves should not cause overspeeding Corrective actions at each of
     these plants involved changing the startup method so that a small steam
     flow admitted through a small bypass line warms the turbine before it 
     is exposed to full steam flow This approach is recommended by General 
     Electric Service Information Letter (SIL) 377, dated June 1, 1982 

2   Entrapped oil in the governor speed setting cylinder 

     As illustrated by an event at Turkey Point 3 (see IE Information Notice
     86-14), turbines with Woodward Model PG-PL governors can overspeed from
     entrapped hydraulic fluid 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 The most 
     commonly used technique to accelerate depressurization is to manually 
     exercise the speed setting knob at the governor This adjustment 
     introduces two possibilities for human error: the operator may 
     inadvertently not fully dump the hydraulic system or may not correctly 
     reset the speed control 

3   Incorrect governor setting 

     Six events occurred during surveillance testing with the governor speed
     set too high without the operators being aware of the errors Two 
     events in which the turbines actuated on automatic safety signals were 
     determined to be caused by the operators' failures to follow procedures 
     and check speed settings Therefore, events involving incorrect 
     governor speed settings may be attributed to an inadequacy in the 
     adjustment and calibration procedures, an operator's failure to follow 
     procedures, or a combination of the two 

4   Water induction into the turbine 

     Condensate adversely affects control of the turbine speed Four PWRs 
     have experienced overspeed trips due to water in the steam supply 
     lines Condensate, containing significantly less energy than an 
     equivalent mass of steam, tends to slow the turbine and cause the 
     governor to open the governor valve further On clearing of the 
     condensate, the governor cannot close the governor valve fast enough to 
     prevent a turbine overspeed trip 


                                                     IN 86-14, Supplement 1 
                                                     December 17, 1986     
                                                     Page 3 of 3           

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 this office 


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

Technical Contact:  C Vernon Hodge, IE
                    (301) 492-7275

                    Chuck Hsu, AEOD
                    (301) 492-4443

Attachment: List of Recently Issued IE Information Notices


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