HomeMy WebLinkAbout851182.tiff SSINS No. : 6835
IN 85-86
UNITED STATES
NUCLEAR REGULATORY COMMISSION ; � 1�v'
OFFICE OF INSPECTION AND ENFORCEMENT ' N0V 91985
WASHINGTON, :, r
.C. I
W tELEV. COLO.
IE INFORMATION NOTICE NO. 85-86: LIGHTNING STRIKES AT NUCLEAR POWER
GENERATING STATIONS
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose: •
This notice is provided to alert recipients of a potentially significant
problem of reactor trips and instrument damage caused by lightning strikes. It
is expected that recipients will review the information for applicability to
their facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities. However, suggestions contained in this
notice do not constitute NRC requirements; therefore, no specific action or
written response is required.
The NRC is continuing to evaluate pertinent information. Recipients of this
notice will be notified of additional information or if specific actions are
required.
Description of Circumstances:
A number of plant trips and instrumentation problems attributable to lightning
have occurred over the past 6 years. Since solid state circuitry designs are
being increasingly employed in safety related systems, the impact of lightning
induced line surges on those circuits is emphasized in this notice. Descrip-
tions of several of the more significant events are presented below. Events
involving lightning strikes of switchyards and the consequential impact on
power distribution systems are not covered by this notice. However, INPO SER
76-84 covers this latter subject as well as summarizing earlier INPO documents
dealing with lightning strikes at nuclear power plants.
Zion Power Station Units 1 and 2
On August 17, 1979, both units tripped simultaneously during a severe lightning
storm. Investigation indicated that a lightning strike in close proximity to
the plant caused either a momentary surge or interruption in the ac power
supply circuits to the rod control power supply cabinets. This transient
tripped the overload protection devices for the dc power supply cabinet,
resulting in a power interruption to the control rod stationary gripper coils,
8511010020 851182
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IN 85-86
November 5, 1985
Page 2 of 4
which caused the rods to drop into the core. The resulting high, negative flux
rate initiated the reactor trip signal . Tests verified that noise induced on
the ac input to one power supply would actuate the overvoltage protection trips
on the main and auxiliary power supplies. In addition to the noise spikes, one
Unit 2, 24-V positive power supply was damaged by the lightning strike and had
to be replaced. The following corrective actions were initiated:
o The control rod system neutral was isolated from the station ground.
o The overvoltage protection trip setting was changed from 27 to 29 V.
o A low-pass filter was installed on the input to each 24-V positive power
supply.
o A volt trap (a voltage suppressor circuit designed to reduce large voltage
surges and noise induced by lightning strikes) was installed across the
50-ohm motor generator neutral resistor.
o A volt trap was installed across the power feed to the auxiliary power
supply.
o The power feed for the auxiliary power supply was changed from the 480-V
system to the control rod drive (CRD) motor generators.
Zion Unit 2 experienced additional reactor trips attributed to lightning on
April 3 and July 16, 1980, before the above listed corrective actions were
implemented. In these cases it was determined that the transient tripped the
overload protection devices, as was the case in the trip of both units on
August 17, 1979. However, no power supplies or other equipment were damaged
during the latter two trips.
Again, on December 2, 1982, Zion Unit 2 reactor tripped from 100% power during
an electrical storm. It was concluded that lightning induced a disturbance in
the electrical system causing a reactor trip from a generator trip. Additional
lightning protection for the containment building was provided and the static
wire associated with the 345-kV line was isolated from the power station
structural steel. -
Salem Power Station Unit 1
On June 8, 1980, the reactor tripped during an electrical storm. Lightning
struck at the south penetration area of reactor containment causing a transient
on seven main steam pressure transmitters. Two of these pressure transmitters
were damaged and had to be replaced. The transient caused a high steam line
pressure differential reactor trip signal and a safety injection signal . The
licensee believes the lightning strike hit main steam vent pipes which extend
above the penetration area roof and the surge was carried into the building via
piping connections.
IN 85-86
November 5, 1985
Page 3 of 4
Kewaunee Power Station
On August 19, 1980, two of four instrument busses lost power during an electri-
cal storm. This resulted in a spurious safety injection (SI) actuation signal ,
and the unit tripped from full power. In addition to inducing the instrumenta-
tion transients, the inverter fuses were blown. These fuses were replaced, and
no other evidence of equipment failure was observed.
Byron Power Station Unit 1
On July 13, 1985, when lightning struck the Unit 1 containment, the reactor
tripped from approximately 11% power because of induced voltage surges in
instrument and control cables in one of four containment penetration areas.
The induced voltage caused failure of four rod drive power supplies, including
1 redundant pair. The failure of the redundant supplies resulted in 10 control
rods dropping into the core. A power range negative-flux-rate reactor trip
resulted from the rod insertion. In addition to the reactor trip, damage
occurred to 30 plant instruments. The following systems were affected by the
damaged instrumentation: protection channel II, one train of the 48-volt power
supply for the solid state protection system, the meteorological tower, control
rod drive, and loose-parts monitoring.
A review of cable routings showed that a significant common denominator existed
in containment penetrations. All damaged instruments were associated with
cables passing through penetrations located in one containment region. In
addition to the damaged instrumentation, the lightning damaged a significant
amount of security equipment.
The licensee determined that an improved lightning protection system was
required to prevent recurrence of a similar incident. By installing copper
conductors, external to containment, from the roof mounted lightning rods
directly to ground rods in the earth, a low impedance path to ground was
provided for future lightning strikes. This modification is similar to the
Zion modification described above.
Arkansas Power Station Unit 2
On August 5, 1985, the reactor tripped from 100% power on a low departure-from-
nucleate-boiling ratio (DNBR) signal as the result of a lightning strike
transient induced in two of the core protection system channels. The licensee' s
followup investigation revealed no damage to the plant' s electrical equipment '
or instrumentation measuring systems.
IN 85-86
November 5, 1985
Page 4 of 4
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.
£4threctDivisEmergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts: Ray
S.790-5593
y2) ov
Vincent D. Thomas, IE
(301) 492-4755
Attachment: List of Recently Issued IE Information Notices
Attachment 1
IN 85-86
November 5, 1985
LIST OF RECENTLY ISSUED
IE INFORMATION NOTICES
Information Date of
Notice No. Subject Issue Issued to
85-85 Systems Interaction Event 10/31/85 All power reactor
Resulting In Reactor System facilities holding
Safety Relief Valve Opening an OL or CP
Following A Fire-Protection
Deluge System Malfunction
85-84 Inadequate Inservice Testing 10/30/85 All power reactor
Of Main Steam Isolation Valves facilities holding
an OL or CP
85-83 Potential Failures Of General 10/30/85 All power reactor
Electric PK-2 Test Blocks facilities holding
an OL or CP
85-82 Diesel Generator Differen- 10/18/85 All power reactor
tial Protection Relay Not facilities holding
Seismically Qualified an OL or CP
85-81 Problems Resulting In 10/17/85 All power reactor
Erroneously High Reading facilities holding
With Panasonic 800 Series an OL or CP and
Thermoluminescent Dosimeters certain material
and fuel cycle
licensees
85-80 Timely Declaration Of An 10/15/85 All power reactor
Emergency Class Implementa- facilities holding
tion Of An Emergency Plan, an OL or CP
And Emergency Notifications
85-17 Possible Sticking Of ASCO 10/1/85 All power reactor
Sup. 1 Solenoid Valves facilities holding
an OL or CP
85-79 Inadequate Communications 9/30/85 All power reactor ,
Between Maintenance, facilities holding
Operations, And Security an OL or CP; research
Personnel and nonpower reactor
facilities; fuel
fabrication and
processing facilities
OL = Operating License
CP = Construction Permit
SSIN No. : 6820
OMB No. : 3150-0011
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UNITED STATES 11711� 2' 1
NUCLEAR REGULATORY COMMISSION j1 �flV 4-9 '.
OFFICE OF INSPECTION AND ENFORCEM/
WASHINGTON, D.C. 20555 t,
GRELLLv, (_�.L'LO.
November 5, 1985
IE BULLETIN NO. 85-02: UNDERVOLTAGE TRIP ATTACHMENTS OF WESTINGHOUSE DB-50
TYPE REACTOR TRIP BREAKERS
Addressees:
All power reactor licensees and appljcants.
Purpose:
The purposes of this bulletin are: to inform all power reactor licensees and
applicants of recent reactor trip breaker reliability problems, to assure that.
licensees of currently operating Westinghouse power reactor facilities that
have not yet installed the automatic shunt trip modification are performing
undervoltage trip attachment (UVTA) force margin testing of the reactor trip
breakers (RTBs) , and to clarify the "OPERABILITY" requirements related to RTBs.
Description of Circumstances
On October 29, 1985, at 13: 57 EST the D. C. Cook Nuclear Station Unit No. 2
tripped from approximately 80% of full power. The reactor trip was triggered
by a spurious indicated low flow condition in loop 2. The trip signal originated
from the reactor coolant pump breaker contacts. Following the reactor trip
condition it was immediately discovered that the reactor trip breaker associated
with Train "A" reactor protection system (RPS) did not open, and the trip
function was accomplished by only the "6" train RT6 (which subsequently on
November 3, 1985 failed to pass the UVTA force margin test). Two of four
safety-related feedwater isolation valves did not close because the actuation
signal to close should have originated from contacts in the failed Train "A"
circuit breaker. The remaining two feedwater isolation valves did operate
properly because the train "B" reactor trip circuit breaker opened and triggered
the isolation action to these two valves. Also, the feedwater regulating valve
in each loop was closed by the "B" train RTB signal .
Subsequent action by the licensee included quarantining the failed Train "A"
reactor trip breaker. This was facilitated by opening the circuit breakers to
the motor-generators.
Investigation into the event by the licensee and Westinghouse attributed the
failure of the Train "A" reactor trip breaker to a faulty undervoltage trip
attachment (UVTA) which did not provide enough lifting force to the breaker
trip bar. The breaker is identified as the Westinghouse Type DB-50.
851 1050230
tad mTq"I]SISS
IEB 85-02
November 5, 1985
Page 2 of 4
Subsequent to the October 29, 1985 incident, all RTBs at the DC Cook station
were tested. UVTA trip force margin testing of the Unit 2 "B" breaker on
November 3, 1985 identified degradation of the margin below the 20 ounce
specified margin (i .e. , the requirment for the UVTA is to exert 50 ounces of
force, 30 ounces to move the trip bar and 20 ounces for margin). The
significance of the degradation of the UVTA attachment of the "B" breaker, in
conjunction with the failure of the "A" breaker to trip on October 29, 1985
renews concern for common mode failures that could potentially lead to an ATWS
event.
Background:
As a result of the February 22 and 25, 1983 Salem anticipated transients
without scram (ATWS) events, the NRC issued IE Bulletin 83-01 and formed a
task force to assess the generic implications of these events. On March 11,
1983, Southern California Edison reported that three GE-manufactured RTBs on
San Onofre Unit 2 and one on Unit 3 failed to open during testing of the UVTA.
As a result of these failures, the NRC issued IE Bulletin 83-04.
The task force' s actions resulted in the issuance of NUREG-1000, "Generic
Implications of the ATWS Events at the Salem Nuclear Power Plant" and Generic
Letter 83-28, delineating the procedural and plant changes required. Findings
in NUREG-1000 were based, in part, on assurances that improved maintenance of
the breakers would improve the reliability of the UVTAs to an acceptable level
for the short term, after which the longer term corrective actions would be
impTemented.
The longer term corrective actions were directed by NRC Generic Letter 83-28.
These actions had two major aspects related to the RTB/UVTAs: (1) the
installation of a plant modification that provides for the automatic activation
of the shunt trip coil of the RTB for any automatic reactor trip signal , and
(2) reliability improvements in the RTB/UVTA based upon UVTA life testing by
the vendor. The life test formed the basis for a UVTA replacement interval
of 1250 cycles and a lubrication interval of 200 cycles.
The recent failures at D. C. Cook Unit 2 involved RTBs that were refurbished
by the vendor only 4 months previously, including the installation of new
UVTAs. The Unit 2 RTB "A" (that failed on October 29, 1985) had experienced
only about 75 operations on the UVTA. The Unit 2 RTB "B" (that failed on
November 3, 1985) had experienced about half as many operations on the UVTA.
In this short time, both UVTAs suffered a serious reduction of their trip
output force.
The Westinghouse specification for the DB-50 breaker specifies a minimum total
force output of the UVTA to be 50 ounces. This total force output provides a
force margin of 20 ounces above the maximum force required to trip the breaker.
The UVTA trip force margin is measured by temporarily hanging a weight on the
trip bar of the breaker and actuating ( i . e. , de-energizing) the UVTA. Many
plants include a force margin test as part of the 18-month surveillance actions.
If the weight is less than the UVTA margin, the UVTA will consistently trip the
breaker. If the weight is greater than the UVTA margin, the UVTA will consistently
not trio the breaker. If the weight approximates the UVTA margin, the UVTA
IEB 85-02
November 5, 1985
Page 3 of 4
will not be consistent in its ability to trip the breaker during the test. At
D.C. Cook, three tests at each weight were used to assure valid test results.
Testing of RTB "A" indicated that the UVTA force margin had fallen to 5 ounces
or less. Testing of the RTB "B" indicated that the UVTA force margin was no
longer as great as 20 ounces. If the UVTA does not have adequate margin, it is
unacceptable and requires replacement or maintenance.
The root cause of the lost force margin is not known at this time; laboratory
failure analysis of the failed UVTAs is being arranged. It is believed that
re-lubrication may temporarily restore some of the lost force.
NRC preliminary information is that 9 Westinghouse PWRs have not yet implemented
the automatic shunt trip modification. As shown in the attachment, only 3 of
these plants are currently operating; namely: Kewaunee, Beaver Valley Unit 1,
and Turkey Point Unit 4.
REQUIRED ACTIONS FOR LICENSEES OF CURRENTLY OPERATING WESTINGHOUSE PWR
FACILITIES THAT HAVE NOT YET IMPLEMENTED THE ACTUATION OF
RTB SHUNT TRIB COIL ON ALL AUTOMATIC REACTOR-TRIP SIGNALS
1. Perform a test of the UVTA of each RTB that is in service to determine
that adequate force margin exists, as soon as practical , but not to exceed
7 days of receipt of this bulletin. With a weight of 20 ounces attached
to the trip bar, the UVTA by itself must trip the RTB three times in
succession. This test shall be performed with the UVTA and breaker in "as
found" conditions, prior to any lubrication or other maintenance. Any
occurrence of a force margin less than 20 ounces defines an unacceptable
UVTA.
2. Modify the monthly test procedure for the Reactor Protection System to
add conducting the UVTA force margin test, prior to any lubrication or
adjustment of the UVTA, for each RTB that is in service. This test is
normally conducted on one RTB each month, i. e. , two months between tests
on the same RTB. If an RTB fails the UVTA force margin test, the redundant
RTB is to be similarly tested within 8 hours. This procedural modification
should be in place for the next such test after receipt of this bulletin •
and remain in force, until the automatic shunt trip modification is fully
implemented.
3. Provide written instructions to the plant operating staff, within 7 days
of receipt of this bulletin, requiring that:
(a) The content of this bulletin be reviewed by each licensed operator at
the start of his/her next duty shift.
(b) A reactor trip breaker shall be declared INOPERABLE, if the UVTA
either does not successfully pass the force margin test or otherwise
may not be capable of performing its intended safety function.
(c) Plant operation with either RTB INOPERABLE shall continue only as
provided for in the plant Technical Specifications.
IEB 85-02
November 5, 1985
Page 4 of 4
(d) The NRC is to be notified via the emergency notification system within
4 hours of any RTB being declared inoperable.
4. Provide a written report to the NRC within 30 days of receipt of this
bulletin, which discusses the specific actions taken pursuant to this
bulletin and the results thereof.
Should a licensee determine that any action requested by this bulletin
jeopardizes overall plant safety, the NRC should be notified of that fact and
provided with appropriate justification for not implementing the requested
action. Such notification shall be made within 7 days of receipt of this
bulletin.
The written reports shall be submitted to the appropriate Regional Administrator
under oath or affirmation under provisions of Section 182a, Atomic Energy Act
of 1954, as amended. Also, the original copy of the cover letters and a copy
of the reports shall be transmitted to the U. S. Nuclear Regulatory Commission,
Document Control Desk, Washington, DC 20555 for reproduction and distribution.
This request for information was approved by the Office of Management and
Budget under a blanket clearance number 3150-0011. Comments on burden and
duplication may be directed to the Office of Management and Budget, Reports
Management, Room 3208, New Executive Office Building, Washington, D. C. 20503.
If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC Regional Office of one of the technical
contacts listed below.
/4^James Taylor, Director
offic f Inspection and Enforcement
Technical Contacts: J. T. Beard, NRR
(301) 492-7465
V. Thomas , IE
(301) 492-4755
Attachments:
1. Facilities Without Automatic Shunt
Trip Installed
2. List of Recently Issued IE Bulletins
Attachment 1
IEB 85-02
November 5, 1985
Page 1 of 1
FACILITIES WITHOUT AUTOMATIC SHUNT TRIP INSTALLED
FACILITY REMARKS
1. .Kewaunee Install in February 1986
2. Beaver Valley Install in May 1986
3. Turkey Point 4 Install in January 1986
4. Sequoyah 2 Currently 5/D; install Spring 1986
startup
5. Sequoyah 1 Currently S/D; will install before
startup
6. North Anna 1 Currently 5/D; will install before
startup
7. Byron 1 Currently S/D; will install before
startup
8. Zion 2 Currently S/D; will install before
startup
9. Cook 2 Will install prior to startup
Attachment 2
IEB 85-02
November 5, 1985
LIST OF RECENTLY ISSUED IE BULLETINS
Bulletin Date of
No. Subject Issue Issued to
85-01 Steam Binding of Auxiliary 10/30/85 All nuclear power
Feedwater Pumps facility licensees
and CP holders.
84-03 Refueling Cavity Water Seal 8/24/84 All power reactor
facilities holding
an OL or CP except
Fort St. Vrain
84-02 Failures Of General Electric 3/12/84 All power reactor
Type HFA Relays In Use In facilities holding
Class 1E Safety System an OL or CP
84-01 Cracks In Boiling Water 2/3/84 All BWR facilities
Reactor Mark I Containment with Mark I contain-
Vent Headers ment and currently
in cold shutdown
with an OL for Action
and All other BWRs
with an OL or CP for
information
83-08 Electrical Circuit Breakers 12/28/83 All power reactor
With An Undervoltage Trip facilities holding
Feature In Use In Safety- an OL or CP
Related Applications Other
Than The Reactor Trip System
83-07 Apparently Fraudulent 12/09/83 Same as IEB 83-07
Sup. 2 Products Sold By Ray Miller,
Inc_
83-07 Apparently Fraudulent 10/26/83 Same as IEB 83-07
Sup. 1 Products Sold By Ray Miller,
Inc.
OL = Operating License
CP = Construction Permit
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