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
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021