Information Notice 1991-83, Solenoid-Operated Valve Failures Resulted in Turbine Overspeed
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s
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.
20555
December 20, 1991
NRC INFORMATION NOTICE 91-83: SOLENOID-OPERATED VALVE FAILURES RESULTED
IN TURBINE OVERSPEED
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice
to alert addressees to turbine overspeed problems and turbine trip failures
resulting from the failures of multiple solenoid-operated valves (SOVs). It is
expected that recipients will review the information for applicability to their
facilities and consider actions, as appropriate, to avoid similar problems.
However, suggestions contained in this information notice are not NRC require- ments; therefore, no specific action or written response is required.
Background
Westinghouse turbines are tripped using a combination of electro-hydraulic
control (EHC) fluid and auto-stop oil (Attachment 1).
In the electro-hydraulic
portion, SOVs dump the fluid to the EHC sump, causing the throttle valves, reheat stop valves, intercept valves, and the governor valves to shut, stopping
the flow of steam to the turbine.
Failure of the SOVs in the EHC system to
open could lead to the turbine overspeeding. Several events have occurred in
the industry that involved the failure of SOVs that must operate for turbine
emergency trip and overspeed protection.
The consequences of these failures
have varied according to the initiating event and the type of SOV failure.
These failures suggest that there are weaknesses in the preventive maintenance
and testing of these SOVs.
Description of Circumstances
On November 9, 1991, Unit 2 of the Salem Nuclear Generating'Station sustained
severe damage to its turbine and generator. The event occurred while'the
Public Service Electric and Gas Company (the licensee) was conducting routine
turbine testing at 100-percent power. The licensee bypassed the turbine's
auto-stop oil trip mechanism in accordance with the test procedure. During the
test, an oil pressure perturbation occurred in the auto-stop trip system, the
exact cause of which is yet to be determined.
This caused the interface valve
to open and thereby depressurized the EHC fluid.
Both the turbine and the
reactor tripped and, as expected, all turbine stop valves closed.
However, the
emergency trip solenoid valve failed to open upon receiving the trip signal.
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-,December 20, 1991 When the auto-stop oil repressurized, the interface valve closed, and all
turbine stop valves reopened allowing steam flow into the turbine.
As
designed, the generator output breakers had opened upon receiving the reactor
trip signal, so the steam flow through the unloaded turbine caused the turbine
to overspeed.
Both overspeed protection controller (OPC) solenoid valves
failed to open preventing the governor valves and intercept valves from closing
properly. The turbine continued to overspeed to an estimated 160-percent of
rated speed.
Operators observed increasing noise and vibration from the
turbine and a fire at the generator.
The low pressure turbine blades penetra- ted the turbine shroud.
The overspeed resulted in severe damage to the low
pressure turbine, the generator exciter unit, the condenser, and associated
support structures, systems, and components.
Discussion
The staff sent an augmented inspection team (AIT)
to the site to investigate
the event.
The AIT concluded that the proximate cause of the event was the
failure of the emergency trip solenoid valve and both overspeed protection
controller solenoid valves to open when energized. The specific failure
mechanisms of the Parker-Hannifin SOVs are yet to be determined, but prelimi- nary analysis indicated that the pilot valve assembly in each solenoid unit was
mechanically bound sufficiently to prevent movement. Other previous failures
of these valves in the industry have also been attributed to mechanical bind- ing, corrosion, and worn or pinched elastomeric parts.
Several precursory factors contributed to the event. The licensee for the
Salem Nuclear Generating Station has no preventive maintenance program for any
of these three SOVs.
The surveillance and operational testing of the turbine
trip and overspeed circuits does not specifically verify the proper hydraulic
functioning of each SOY independently.
Further, information concerning previ- ous SOV failures has not been well disseminated.
The licensee had two earlier indications of problems with these SOVs.
Similar
valves on Salem Unit 1 required replacement, yet the licensee had not effec- tively verified the operability of the SOYs in Unit 2. Another indication
occurred during a startup in October 1991.
The OPC solenoid valves failed to
open when a test of the system was performed.
The licensee was required to
verify proper OPC operation by closing the intercept valves when the OPC test
switch was activated. The intercept valves did not close, indicating a possi- ble malfunction of both of the OPC solenoid valves. The results were
apparently misinterpreted, leading management to believe a procedure problem
existed, rather than an equipment problem.
The licensee continued the startup
without further diagnosis and resolution.
The staff will include more details
of this event in NRC Inspection Report 50-311/91-81 when issued.
Previous Events
The following previous events involved failures of SOVs in the turbine trip
system during reactor trip events:
On April 6, 1985, at the R. E. Ginna Nuclear Power Plant, the turbine failed to
trip automatically following a reactor trip because of mechanical binding of
the emergency trip solenoid valve.
-
IN 91-83 December 20, 1991 On February 28, 1988, at the Crystal River Plant, Unit 3, the turbine failed to
trip automatically following a reactor trip because of a faulty emergency trip
On September 10, 1990, at Salem, Unit 1, the reactor tripped because of a steam
generator water level transient caused by a spurious overspeed signal.
Mechan- ical binding prevented the OPC solenoid valves from functioning.
On September 29, 1990, at Ginna, the reactor tripped because of personnel
error, but mechanical binding prevented the turbine emergency trip solenoid
valve from functioning.
These events indicate that proper maintenance and operability testing of both
the emergency trip solenoid valve and the OPC solenoid valves is prudent.
Related Generic Communications
The staff issued Generic Letter 91-15, "Operating Experience Feedback Report, Solenoid-Operated Valve Problems at U.S. Reactors," to distribute NUREG-1275, Volume 6, to industry. This document provided the staff's analysis of recent
U.S. light water reactor experience (primarily 1984-1989) with SOYs.
Appendix A of NUREG-1275, Volume 6, cited similar SOV failures at four other
plants. The staff noted the susceptibility of SOVs to common-mode failures.
The staff found that most SOVs cannot tolerate contaminants, need preventative
maintenance or periodic replacement, and have a propensity for rapid aging and
deterioration when subjected to elevated temperatures. The staff provided
recommendations to aid in preventing common-mode SOV failures.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact one
of the technical contacts listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
Charles E. Rossi, Dir
or
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts:
John White, Region I
(215) 337-5114
David Gamberoni, NRR
(301) 504-1171 Attachments:
1. Westinghouse Electro-Hydraulic Control System
2. List of Recently Issued NRC Information Notices
II
EMERGENCY TRIP
TO EHC
C
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AUTO-STOP OIL SYSTEM
TO En-IC
SUIMP
INTERFA'
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ELECTRO-HYORAULIC CONTROL FLUID
................
AUTO-STOP OIL
TO EHC
SUAJP
OVERSPEED PROTECTION
CONTROLLER SOLENOID
VALVES
WESTINGHOUSE ELECTRO-HYDRAULIC CONTROL SYSTEM
(D Z r'
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'\\Attachment 2 IN 91-83
December 20, 1991 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
91-18, Supp. 1
91-82
91-81
91-80
91-79 High-Energy Piping Failures
Caused by Wall Thinning
Problems with Diaphragms
in Safety-Related Tanks
Switchyard Problems that
Contribute to Loss of
Offsite Power
Failure of Anchor
Head Threads on Post-
Tensioning System During
Surveillance Inspection
Deficiencies in the
Procedures for Instal- ling Thermo-Lag Fire
Barrier Materials
Potential for Spent
Fuel Pool Draindown
Status Indication of
Control Power for
Circuit Breakers Used
in Safety-Related Appli- cations
Substandard, Refur- bished Potter & Brum- field Relays Repre- sented as New
Shift Staffing at
Nuclear Power Plants
12/18/91
All holders of OLs or CPs
for nuclear power reactors.
12/18/91
All holders of OLs or CPs
for nuclear power reactors.
12/16/91
All holders of OLs or CPs
for nuclear power reactors.
12/11/91
All holders of OLs or CPs
for nuclear power reactors.
12/06/91
All holders of OLs or CPs
for nuclear power reactors.
11/29/91
All holders of OLs or CPs
for nuclear power reactors.
11/28/91
All holders of OLs or CPs
for nuclear power reactors.
11/27/91
All holders of OLs or CPs
for nuclear power reactors.
11/26/91
All holders of OLs or CPs
for nuclear power reactors.
88-92, Supp. 1
91-78
90-57, Supp. 1
91-77 OL = Operating License
CP = Construction Permit
HE
UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D.C. 20555
OFFICIAL BUSINESS
PENALTY FOR PRIVATE USE, $300
FIRST CLASS MAIL
POSTAGE 6 FEES PAID
PERMIT No 0-57 I
II
IN 91-83 December 20, 1991 On February 28, 1988, at the Crystal River Plant, Unit 3, the turbine failed to
trip automatically following a reactor trip because of a faulty emergency trip
On September 10, 1990, at Salem, Unit 1, the reactor tripped because of a steam
generator water level transient caused by a spurious overspeed signal. Mechan- ical binding prevented the OPC solenoid valves from functioning.
On September 29, 1990, at Ginna, the reactor tripped because of personnel
error, but mechanical binding prevented the turbine emergency trip solenoid
valve from functioning.
These events indicate that proper maintenance and operability testing of both
the emergency trip solenoid valve and the OPC solenoid valves is prudent.
Related Generic Communications
The staff issued Generic Letter 91-15, "Operating Experience Feedback Report, Solenoid-Operated Valve Problems at U.S. Reactors," to distribute NUREG-1275, Volume 6, to industry. This document provided the staff's analysis of recent
U.S. light water reactor experience (primarily 1984-1989) with SOVs.
Appendix A of NUREG-1275, Volume 6, cited similar SOV failures at four other
plants. The staff noted the susceptibility of SOVs to common-mode failures.
The staff found that most SOVs cannot tolerate contaminants, need preventative
maintenance or periodic replacement, and have a propensity for rapid aging and
deterioration when subjected to elevated temperatures. The staff provided
recommendations to aid in preventing common-mode SOV failures.
This information notice requires no specific action or written response.
If
you have any questions about the information in this notice, please contact one
of the technical contacts listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
Charles E. Rossi, Direc r
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts:
John White, Region I
(215) 337-5114
David Gamberoni, NRR
(301) 504-1171 Attachments:
1. Westinghouse Electro-Hydraulic Control System
2. List of Recently Issued NRC Information Notices
Document Name: IN 91-83
- SEE PREVIOUS CONCURRENCES
- REGION I
- EAB:DOEA:NRR
- SC:REGION I
- SC:EAB:DOEA:NRR
IMoghissi
DGamberoni
JWhite
DFischer
12/05/91
12/09/91
12/10/91
12/13/91
- C.-AB DOEA:NRR *Tech Ed
- C:OGCB:DOEA:NRR D:DOEA:NR eI4 g
A~natTee
CBerlinqer
CRossi
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12/13/91
12/10/91
12/13/91
12,y4,91
IN 91-XX
December xx, 1991 On September 10, 1990, at Salem, Unit 1, the reactor tripped because of a steam
generator water level transient caused by a spurious overspeed signal.
Mechanical
binding prevented the OPC solenoid valves from functioning.
On September 29, 1990, at Ginna, the reactor tripped because of personnel
error, but mechanical binding prevented the turbine emergency trip solenoid
valve from functioning.
These events indicate that proper maintenance and operability testing of both
the emergency trip solenoid valve and the OPC solenoid valves is prudent.
Related Generic Communications
The staff issued Generic Letter 91-15, "Operating Experience Feedback Report, Solenoid-Operated Valve Problems at U.S. Reactors," to distribute NUREG-1275 to
industry. This document provided the staff's analysis of recent U.S. light
water reactor experience (primarily 1984-1989) with SOVs. The staff found that
most SOVs cannot tolerate contaminants, need preventative maintenance or
periodic replacement, and have a propensity for rapid aging and deterioration
when subjected to elevated temperatures. The staff provided recommendations to
aid in preventing further SOV problems.
This information notice requires no specific action or written response.
If
you have any questions about the information in this notice, please contact one
of the technical contacts listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: John White, Region I
(215) 337-5114
David Gamberoni, NRR
(301) 504-1171 Attachments:
1. Westinghouse Electro-Hydraulic Control System
2. List of Recently Issued NRC Information Notices
OFC : *REGION I
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- SC: AB:DOEA:NRR :
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Document Name IN91/SALEM
-3-
9/10/90 At Salem, Unit 1, the reactor tripped due to a steam generator water
level transient caused by a spurious overspeed signal.
The OPC solenoid valves
did not function due to mechanical binding.
9/29/90 At Ginna, the reactor tripped due to personnel error, but the turbine
emergency trip solenoid valve failed to function due to mechanical binding.
It is apparent from these events that proper maintenance and operability
testing of both the ET solenoid valve and the OPC solenoid valves is prudent.
Related Generic Communications
NUREG-1275, Operating Experience Feedback Report - Solenoid-Operated Valve
Problems, which was distributed to industry via Generic Letter 91-15, analyzed
recent U.S. light-water reactor experience (primarily 1984-1989) with solenoid- operated valves (SOVs). It was found that most SOVs cannot tolerate contaminants, need preventative maintenance or periodic replacement, and have a propensity
for rapid aging and deterioration when subjected to elevated temperatures.
Various recommendations were provided to aid in the prevention of further SOV
problems.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact one
of the technical contacts listed below or the appropriate Office of Nuclear
Reactor Regulation project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: John White, Region I
(215) 337-5114
David Gamberoni, NRR
(301) 492-1171 Attachments:
1. List of Recently Issued NRC Information Notices
OFC :
REGION I
- EAB:DOEA:NRR
SC:REGION I : SC:EAB:DOEA:NRR
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NAME :
IMoghissi
- DGamberoni wt
- JWhite
- DFischer
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DATE:
/ /91
// /91
/ /91
/ /91 OFC : C:EAB:DOEA:NRR :
Tech Ed
C:OGCB:DOEA:NRR : D:DOEA:NRR
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NAME : AChaffee
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--------- I------- -----------------: ----------
DATE:
/ /91
12- /I/91
/ /91
/ /91 OFFICIAL RECORD COPY
-( SEE PREV10ouS
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Document Name
IN91/SALEM
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9/1/g10 At Salem, Unit 1, the reactor tripped due to a
levtI transient caused by A spurious overspeed signal.
did not function due to mechanical binding, The:OPC $07eno
atves
9/29/90 At ronnh
the reactor tripped due to personnel error, but
emgen"y trip So50nojd V8lve failed to function due to mechanical the turbine
bindinn.
It Is apparent from thes *vents that proper maintenance and operability
testing of both the ET solenoid valve and the OPC Solenoid valves Is prudent&
Related Generic Commnunicctiong
NORO-1275 ,perating Ex erieng Feedback eportave
wbems
wh c was
strbuzec onustry via gener
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recent US. light-water reactor experience (primarily 1984.198g) WitY solenoid.
operated vatves (SOVi)t It WAs found that most SOYs cannot tolerate contaminants, need preventativ maintenance or periodic replacement
and have a propensity
for rapid aging and deterioration when subjected to elevated tomPeratures.
Various raconmendatlons were provided to aid in the prevention of further $01 problems.
This Information notice requires no 8pecfic Action or written response.
If
you have any questions about the Information in
this notice please contact one
of the technical contacts listed below or the appropriate Of ice of Nuclear
Reactor Regulition project manager, Charl'es £, Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts:
John White
Region I
(215) 337-1114 n
' (ba\\id Gamberoni, NRR
(301) 492-1171
Attachmentst
1. List of Recently Issued NRC Information Notices
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At Salem, Unit 1, the reactor tripped due to a steam enerator water
level transient caused by a spurious overspeed signal. The DPC solenoid valves
did not function due to mechanical binding.
9/W9/9O
At Ginna the reactor tripped due to personnel error, but the turbine
emergency trip soienoid valve failed to function due to mechanical binding.
It is apparent from these events that proper maintenance and operability
testing of both the ET solenoid valve and the OPC solenoid valves is prudent.
Related Generic Communications
NUREG-1275, OperatingExperience Feedback Report -
lenoid-Operated Valve
Problems, wh-lc
was d1strlbuteto industry
te
recent US. light-water reactor experience (primarily 1984-1989) with solenoid- operated valves (SOYs), It was found that most $0SY
cannot tolerate contaminants, need preventative maintenance or periodic replacement and have 4 propensity
for rapid aging and deterioration when subjected to *e1vated temnperatures.
Various recommendations were provided to aid in the prevention of further SOY
problems.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice please contact one
of the technical contacts listed below or the appropriate Office of Nuclear
Reactor Regulation project manager.
Charles E. Rossi, Director
Division of 0 eratlonal Events Assessment
Office of Nuc ear Reactor Regulation
Technical contacts: 4ohn White
Region I
(215) 337.h114
David Gamberoni, NRA
(301) 492-1171
Attachmentss
1. List of Recently Issued NRC Informatlon Notices
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