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ACCESSION NBR:9707280243 DOC.DATE: 97/07/21 NOTARIZED: NO DOCKET
# FACIL 50-269 Oconee Nuclear Station, Unit 1, Duke Power Co.
05000269 AUTH.NAME AUTHOR AFFILIATION
BOND,R.T. Duke Power Co. MCCOLLUM,W.R. Duke Power Co. RECIP.NAME
RECIPIENT AFFILIATION
SUBJECT: LER 97-006-00:on 970620,loss of dedicated line from Lee
resulted in loss of power to Unit 1 was noted.Caused by C
inappropriate personnel action.Oconee Unit 1 essential loads were
restored following loss of Lee.W/970721 ltr. A
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Duke Power Company k A Duke Energy Company PrOWef Oconee Nuclear
Site
A DkeE-V -pa"P.O. Box 1439 Seneca, SC 29679
W R. McCollum, Jr. (864) 885-3107 OFFICE Vce President (864)
885-3564 FAx
July 21, 1997
U.S. Nuclear Regulatory Commission Document Control Desk
Washington, D.C. 20555
Subject: Oconee Nuclear Station Docket Nos. 50-269, -270,
-287
Voluntary Licensee Event Report 269/97-06 Problem Investigation
Process No.: 6-097-1906
Gentlemen:
This Voluntary Licensee Event Report (LER) 269/97-06, concerning
the loss of Lee, Failure of Keowee 1, and loss of Keowee 1
auxiliaries, is provided for your information.
This condition is considered to be of no significance with
respect to the health and safety of the public.
Very truly yours,
R. McCollum, J
Attachment
9707280243 970721 PDR ADOCK 05000269
a 4 A 1 A *
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Document Control Desk July 21, 1997 Page 2
cc: Mr. Luis A. Reyes Administrator, Region II U.S. Nuclear
Regulatory Commission 61 Forsyth Street, S. W., Suite 23T85
Atlanta, GA 30303
Mr. D. E. LaBarge U.S. Nuclear Regulatory Commission Office of
Nuclear Reactor Regulation Washington, D.C. 20555
INPO Records Center 700 Galleria Parkway, NW Atlanta, GA
30339-5957
Mr. M. A. Scott NRC Resident Inspector Oconee Nuclear
Station
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FACILITY NAME (1) DOCKET NUMBER (2) PAGE (3) Oconee Nuclear
Station, Unit One 05000 269 1 of 18
TITLE(4) Voluntary LER on Problems During Electrical Tests: Loss
of LEE, Failure of Keowee 1, and Loss of Keowee 1 Auxiliaries
EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES
INVOLVED (8) MONTH DAY YEAR YEAR SEQUENTIAL REVISION MONTH DAY YEAR
FACILITY NAME DOCKET NUMBER(S) NUMBER NUMBER
Oconee, Unit Two 05000 270 06 20 97 97 - 06 - 00 07 21 97
Oconee, Unit Three 1 _____ ____ ___ __ ____________ J05000 287
OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS
OF 10 CFR (Check one or more of the following) (11) MODE (9) N
20.402(b) 20.405(c) 50.73(a)(2)(iv) 73.71(b)
POWER 20.405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 7371(c) LEVEL
(10) 00 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vii) X OTHER
(Specifyin
20.405(a)(1)(iii) 50.73(a)(2)(i) 50.73(a)(2)(viii)(A) Abstract
below and 20.405(a)(1)(iv) 50.73(a)(2)(ii) 50.73(a)(2)(viii)(B) in
Text, NRC Form 20.405(a)(1)(v) 50.73(a)(2)(iii) 50.73(a)(2)(x)
366A)
LICENSEE CONTACT FOR THIS LER (12) NAME TELEPHONE NUMBER
AREA CODE
R. T. Bond, Safety Review Manager
COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS
REPORT (13)
CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE CAUSE SYSTEM
COMPONENT MANUFACTURER REPORTABLE TO NPRDS TO NPRDS
SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED MONTH DAY YEAR
SUBMISSION
YES (f yes, complete EXPECTED SUBMISSION DATE) X NO DATE (15)
ABSTRACT (Limit to 1400 spaces, i.e. approximately fifteen
single-space typewritten lines) (16)
On June 20, 1997, Oconee Unit 1 was at cold shutdown, Unit 2 was
at 100% Full Power, and Unit 3 was at 13% Full Power. As part of a
required test., the Lee Steam Station Switchyard was supplying
power to Oconee Unit 1. At 1244 hours, a loss of the dedicated line
from Lee resulted in a loss of power to Unit 1. Unit 1
automatically swapped to the Oconee switchyard and power was
restored. Both Keowee Hydro (KH) Units (emergency generators)
received a start signal, but KH-1 failed to energize the
underground path. On June 23, 1997, the Lee test was repeated
successfully. However, KH-1 lost auxiliary power during
realignment. The loss of power from Lee resulted from inappropriate
action. KH-1 failed to energize the underground path apparently due
to failure of the field flash breaker to latch. The loss of
auxiliary power was due to equipment failure and a deficient
procedure. Corrective actions have addressed all these causes. This
event did nob impact the health and safety of the public. This is a
voluntary report.
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Oconee Nuclear Station, Unit One 269 97 .06 00 2 OF 18
Background
At Oconee Nuclear Station, Keowee Hydro (KH) Station [EIIS:EK]
serves the emergency power function typically performed by diesel
generators at other nuclear stations. KH consists of two
hydroelectric turbine/generator units and associated support
equipment and auxiliaries. Each KH unit is provided with its own
automatic start equipment. Both units undergo a simultaneous
automatic emergency start and run in standby on a loss of the grid,
an Engineered Safeguards (ES) actuation on any of the three Oconee
Units, or an extended loss of voltage on any Oconee unit's Main
Feeder Buses. On an emergency automatic start, one unit connected
to the underground path supplies the Stand-by Bus while the other
unit, remaining in standby, is available to supply the overhead
path.
When Keowee is unavailable, a 100 KV transmission line can be
dedicated to provide power from one of the Lee Steam Station
combustion turbines (CT). (See Attachment 1.)
Each Oconee unit is provided with several sources of normal and
backup electrical power as described below.
The Normal Source is powered from the Oconee unit's generator
via an Auxiliary Transformer through the Normal ("N") Breakers.
The Start-Up Source is powered via a Start-up Transformer from
the 230 KV Switchyard (SWYD) or from the "overhead" emergency power
path from one KH unit, using the SWYD Yellow bus. The Start-up
("E") Breakers connect it to the unit's two Main Feeder Buses.
The Stand-By Source (Stand-by Bus) is powered from KH via an
underground feeder and transformer CT4 through the "SK" Breakers or
from Lee Steam Station or the Central Switchyard via transformer
CT5 through the "SL" Breakers. The Stand-by ("S") Breakers connect
the Stand-by Bus to the unit's two Main Feeder Buses.
Each Oconee unit's power sources are monitored by the Emergency
Power Switching Logic (EPSL) and the Main Feeder Bus Monitor Panels
(MFBMP). These systems will automatically initiate transfer between
the Start-up and Stand-by sources as necessary to supply power. The
selection logic and timing vary depending on the incident
scenario.
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Oconee Nuclear Station, Unit One 269 97 06 00 3 OF 18
Technical Specification (TS) 3.7 requires both KH units and both
power paths from KH to be operable. One path may be removed from
service for 72 hours if the other path is verified to be operable
within one hour and every eight hours thereafter. Both KH units may
be inoperable for up to 72 hours for planned reasons if the standby
buses are first energized from CT-5 transformer using the dedicated
line from the Lee CT's. This last limiting condition for operation
is reduced to 24 hours if both KH units are inoperable for
unplanned reasons and the Standby Bus is energized from a dedicated
Lee CT within 1 hour.
Lee Steam Station operations group is staffed with 5 operators
and 1 Production Team Leader per shift. There is one control room
for operation of three coal fired units. Lee also has three
combustion turbines which are operated from local control
panels.
Event Description
On June 20, 1997, Unit 1 was at cold shutdown, Unit 2 was at
100% Full Power, and Unit 3 was at 13% Full Power, with its
turbine/generator off line.
Oconee Nuclear Station (ONS) personnel were performing
PT/l/A/0610/06 "100KV Power Supply from Lee Steam Station". Because
it has typically been performed during refueling conditions, this
performance of the test was classified as an "infrequently
performed test or evolution" which required additional procedural
provisions -such as enhanced management oversight, contingency
plans, etc. Lee Steam Station personnel were supporting this test
by performing a Lee operating procedure titled "Emergency Power or
Back-up Power to Oconee.".
ONS had been aligned with the Lee Switchyard supplying power to
the Unit 1 Main Feeder Busses via the SL and S breakers. Per step
12.8.2, substep 4, ONS had notified Lee that Central Switchyard was
aligned for Oconee to receive power from the operating combustion
turbine (CT). This isolated the 100 KV Lee line from the Central
Switchyard.
At Lee, all three coal fired units were in operation during
thiss test. Of the three combustion turbines, only 6C, the CT
involved in this test, was in operation.
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Oconee Nuclear Station, Unit One 269 97 06 00 4 OF 18
The Lee Process Team Leader (PTL) (equivalent to Operations
Shift Manager) and a Technical Specialist (from the station support
staff) were performing steps at the local control panel for the CT.
Lee Operator A (LOA)(a Control Operator) and Lee Operator B (LOB)
(an Assistant Control Operator) were performing steps in the Lee
control room. LOB had little experience with the Lee procedure to
support Oconee, and was participating under LOA's direction as part
of an informal training activity.
The other operators on this shift were performing duties outside
the common control room during the test. Therefore, LOA and LOB
were responsible for responding to any alarms received on any of
the coal fired units, performing any required control room actions
to support the test, and coordinating communications between
Oconee, the personnel at the CT local control panel, and the other
three operators for their tasks. Interviews subsequent to the event
revealed that, while participating in this test, LOA and LOB had
responded to 56 alarms on the coal units (mostly nuisance alarms on
Unit 3) and 8 to 10 phone calls (several of which were related to
the test).
The Lee operators had started the 6C CT and had paralleled to
the grid per Enclosure 6.1 of the Lee Operating Procedure. LOA and
LOB were intending to perform steps 6.1.5 and 6.1.6, which close
the 89-3 switcher (connecting the CT to the line to Oconee) then
open the 89-2 switcher (disconnecting the CT from the rest of the
Lee switchyard).
LOA stated that he received the phone call from Oconee stating
that the lineup at Central was complete. He silently read the
procedure steps, extracted the actual actions to be performed, then
verbally directed LOB to perform the necessary actions. At
approximately 1244 hours, LOB opened 89-2 then closed 89-3 within
approximately 3 seconds (opposite from the sequence required by the
procedure).
This caused the CT to be separated from the grid, then
reconnected. This resulted in a 50G instantaneous ground protective
relay tripping open the OCB-13 Central White breaker, disconnecting
the Oconee-Lee dedicated line from the rest of the grid. The
breaker operations isolated the CT, and it continued to run with no
load.
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Y NUMBER NUMBER Oconee Nuclear Station, Unit One 269 97 06 00 5
OF 18
At Oconee, the resulting undervoltage tripped the SL breakers
isolating the Unit 1 Main Feeder Busses (MFB), and initiated timing
for the MFB Monitor Panel channels. After approximately 20 seconds,
the Monitor Panels actuated a Keowee Emergency Start signal and,
following an additional one second time delay, a Load Shed.
Upon receipt of the Load Shed signal, Emergency Power Switching
Logic (EPSL) initiated the Retransfer to Start-up timers since the
S breakers were closed with the Standby Bus deenergized. After a
five second time delay, the S breakers opened and the E breakers
closed, powering the MFBs from the Oconee switchyard.
Keowee Unit 2 (KH-2) was aligned to the overhead path. It
successfully started, but did not need to close into the switchyard
Yellow Bus since there was no associated Loss of Switchyard
event.
Keowee Unit 1 (KH-1) was aligned to the underground path, but
failed to energize CT-4. A Failure Investigation Process (FIP) team
was initiated to investigate this failure.
In accordance with the contingency plan included in
PT/1/A/0610/06, the Oconee operators verified that power was
restored and began realigning lost loads as necessary, using the
Loss Of Power Abnormal Procedure.
The Operators recognized that the failure of KH-1 to energize
the underground power path made that path inoperable. This placed
Oconee Units 2 and 3 into a LCO per TS 3.7.2(a)l which required
that the available Keowee power path be tested within one hour.
However, the test procedure was not performed within one hour
because KH-2 was currently operating in stand-by with no load.
Rather than shut it down to perform a test, it was considered more
conservative to keep KH-2 operating until more was known about the
loss of power and the failure mode of KH-1. The Operators entered a
more restrictive LCO per TS 3.7.3 which required that Units 2 and 3
be at hot shutdown within 12 hours. The overhead path was tested at
1847 hours, which allowed the Oconee units to exit the 12 hour
LCO.
Due to the importance of Keowee as Oconee's emergency power
source, the Emergency Notification System (ENS) was used at 1605
hours to notify the NRC of the failure of KH-1 to emergency
start.
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Oconee Nuclear Station, Unit One 269 97 E0 00 6 OF 18
In the event of a LOCA, the Engineered Safeguards system will
initiate emergency start signals to both Keowee Units and enable
immediate load shed in the event of a concurrent Loss of Offsite
Power. However, the Main Feeder Bus Monitor Panel provides an
alternate, non-Engineered Safeguards, system to provide initiation
signals for emergency start and load shed after an appropriate time
delay. Therefore, in accordance with guidance given in Nureg 1022,
this event was not considered reportable as an Engineered Safety
Feature (ESF) actuation because it was not initiated by an ESF
signal.
The loss of power to the Unit 1 MFBs existed for approximately
26 seconds. The Oconee Emergency Plan specifies that power must be
lost for more that 15 minutes before an Unusual Event is declared.
Therefore, the event is not reportable as an Unusual Event.
The Keowee failure was not considered reportable because it was
a single component and affected only one power path.
Therefore, the ENS report was considered a voluntary report.
The FIP investigation into the failure of KH-1 to successfully
start began with troubleshooting of the field flash breaker and its
control circuit. The negative leg control power fuse for the KH-1
field flash breaker control circuit was found blown. The FIP team
investigated further to determine the cause of the blown fuse.
The FIP team initially suspected fuse degradation as the cause
due to the age and class of fuse. However, subsequent evaluation
indicated that the fuse had blown.on overload. Fuse Time versus
Current curve corrections for a higher ambient temperature and
allowance for curve tolerances indicate that the fuse might blow in
as little as 5 seconds. However, evaluation of the breaker closing
times indicate the total time spent at peak current was less than
five seconds unless the controls failed to interrupt current to the
close coil. Therefore, the FIP concluded that it was improbable
that the fuse blew due to degradation alone.
In parallel with the fuse evaluation, the field flash breaker
was tested .electrically and mechanically, including Keowee manual
and automatic starts and one emergency start.
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Oconee Nuclear Station, Unit One 269 97 06 00 7 OF 18
During the emergency start test it was observed that the field
flash breaker cycled during the emergency start actuation. Although
not an optimal design, the cycling of the field flash breaker
during emergency starts did not specifically prevent the Keowee
units from performing successful emergency starts as evident by
tests prior to and after the event.
The FIP concluded that the breaker close coil could remain
energized if the breaker failed to latch due to reaching a "trip
free" condition. "Trip free" refers to a condition of the breaker
brought about by attempting to close the breaker with a trip signal
present. Trip latch bounce can also cause the breaker to fail in
the trip free condition. Trip latch bounce is usually random.
The FIP team concluded that a trip free condition probably
occurred when the breaker opened the last time and.caused the
breaker close coil to remain energized until the fuse blew. The FIP
team final report is still under review. The final report will
contain additional technical detail to support the FIP
conclusions.
On June 23, 1997, PT/l/A/610/06 was performed again since it had
not been successfully completed on June 20. During this test, Lee
successfully supplied power and met the procedure acceptance
criteria.
However, a problem occurred during the post-test electrical
system restoration. Oconee Unit 1 switchgear 1TC was deenergized
during a planned dead bus transfer as part of the electrical system
realignment. One of the loads fed by ITC is an underground feeder
which was supplying KH-1 600 V auxiliary power loadcenter 1X via
transformer CX and ACB-7. Following the dead bus transfer, ACB-7
was expected to close automatically to restore power to lX, but it
did not and a lockout of 1X loadcenter occurred. The Keowee
operator noted that no protective relay targets had been received.
This indicated that no faults existed on lX. In accordance with the
-applicable alarm response guide, the operator reset the lockout
relay. Once the lockout relay was reset, ACB-5 and ACB-7 both
attempted to close simultaneously. As they attempted to close, they
were tripped by interlocks. Subsequently, control fuses for both
breakers were found blown. KH-1 was declared inoperable at 1750
hours.
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Oconee Nuclear Station, Unit One 269 97 06 00 8 OF 18
Another FIP was initiated to investigate this failure. This FIP
found that, when power was interrupted to 1TC, ACB-7 tripped open,
as expected. When power was restored to 1TC and CX, ACB-7 attempted
to reclose. One feature of the ACB control circuits is a "Y" relay.
This is an anti-pump relay which is supposed to allow sufficient
time for the breaker to fully close and latch before interrupting
the circuit. In this event, the "Y" relay operated too soon because
its time delay timer failed. This interrupted control power to
ACB-7's close coil, causing the breaker to stop prior to full
closure, and to trip open. Under the existing conditions, a
mechanical linkage initiated a lockout, which tripped ACB-7 and
prohibited ACB-5 and/or ACB-7 from closing.
Once the lockout occurred, a 30 second timer timed out allowing
automatic transfer logic to provide a close permissive to ACB-5.
ACB-7 still had a close permissive due to being previously closed
and in automatic. Therefore, when the lockout was reset, both ACB-5
and ACB-7 had close signals present. As the breakers began to
close, the interlocks between ACB-5 and ACB-7 actuated and tripped
both ACBs. However, the ACBs tripped before the "Y" relay in each
ACB could energize and drop out the "X" relay and closing coil.
This is a trip free condition as described above. This left the
close coil circuits energized and the 10 amp close coil fuses
(Gould OT10) opened as designed.
Based on these findings, the "Y" timer was replaced on ACB-7.
Additionally, a spare breaker with a new "Y" timer was.installed on
ACB-5. The "Y" timers on ACB-6 and ACB-8 (on KH-2) were verified
operable. The close coil circuit fuses in ACB-5 and ACB-7 were
replaced. The alarm response manual was revised to require placing
the automatic transfer logic in manual prior to resetting the
lockout relay. This will preclude both auxiliary power breakers
from having simultaneous close signals as occurred in this
event.
The failed "Y" timer was examined, and it was determined that a
time delay adjustment potentiometer had a short, which resulted in
a very low time
i delay which allowed the timer to deenergize the close coil
prior to the '. 7breaker fully closing.
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FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) YEAR
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NUMBER NUMBER
Oconee Nuclear Station, Unit One 269 97 06 00 9 OF 18
Conclusions
Loss of Power from Lee:
The root cause of the loss of power from Lee was determined to
be inappropriate personnel action due to failure to follow the
procedure correctly.
Lee Operator A (LOA) recognized that the event had occurred and
realized that his thumb (which he was using as a placekeeping aid)
had moved on the procedure page, allowing him to get on the wrong
step. As a result, he had misread the switcher sequence and
misdirected LOB. LOB performed as directed.
There were several factors contributing to this inappropriate
action.
1. It is apparent that there were a high number of job
distractions during the test. LOA and LOB did not seek redirection
of the available resources. For example, they could have called (or
requested that supervision call) one of the other operators to take
over monitoring of the coal fired units or they could have decided
that it was just "too busy" to allow LOB to participate, and freed
him to monitor the other units.
2. Based on interviews after the event, LOA and LOB did not
appear to use human performance aids (such as STAR, touch the
label, repeat back, independent verification, etc.) which have
become expected in the nuclear culture.
3. Although the procedure steps provided adequate direction, the
overall procedure format did not include Human Performance
enhancements typically used in the nuclear culture.
Keowee Unit 1 Failure (June 20):
. The FIP team concluded the fuse probably experienced an
overload condition due to the breaker being in a trip free
condition with a close signal applied.
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Oconee Nuclear Station, Unit One 269 97 06 00 10 OF 18
Keowee Unit 1 Auxiliary Power Failure (June 23)
There were two root causes associated with this event.
1. Equipment failure of the "Y" relay timer adjustment
potentiometer in the ACB-7 control circuit. This is considered the
random failure of an electrical component. There is no history of
similar failures to indicate that this is a recurring problem.
2. Deficient Procedure: The Lockout alarm response manual did
not provide adequate direction for the condition where both
breakers would have close signals when the lockout was reset.
Inappropriate action, specifically procedure adherence, is an
identified problem at Oconee. However, prior events affecting
Oconee have not involved Lee Steam Station personnel.
There have been several events involving unanticipated system
interactions. However, none have involved Keowee within the last
two years.
There have been no other events involving deficient alarm
response manuals within the last two years.
Therefore, none of these events are considered recurring.
None of these events involved personnel injury, radioactive
releases or exposures.
Corrective Actions
Immediate
1. Oconee Unit 1 essential loads were restored following the
loss of Lee on June 20, 1997.'
f2. The test procedure was exited and Oconee Unit 1 was returned
to its pretest alignment.
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Oconee Nuclear Station, Unit One 269 97 06 00 11 OF 18
Subsequent
1.The Keowee Unit 1 blown field flash breaker control fuse was
replaced. Keowee Unit 1 was restored to operable status after
appropriate troubleshooting and testing.
2.Management implemented an interim policy to replace the field
flash breaker control fuses after each Keowee emergency start.
Subsequently, a design modification was implemented to eliminate
the unnecessary cycling of field flash breakers during Keowee
emergency starts.
3. The failed "Y" timer in ACB-7 and the blown fuses in ACB-5
and ACB-7 were replaced. Also, a spare breaker with a new "Y" timer
was installed in ACB5 and the "Y" timers in ACB-6 and ACB-8 were
verified operable.
4. The alarm response guide for this lockout was revised to
require placing the automatic transfer logic in manual prior to
resetting the lockout relay. This will preclude both auxiliary
breakers from having a close signal at the same time.
Planned
1. Oconee Site will provide assistance to Lee Steam Station as
needed to: A) implement human factors improvements affecting
procedures related to backup power to Oconee in the following
areas: * procedure formatting * error reduction techniques (e.g.,
STAR) * reduction/avoidance of distractions
B) evaluate the Oconee/Lee organizational interface to maintain
an appropriate level of awareness and to apply Oconee/nuclear human
performance programs/enhancements at Lee to the extent appropriate
to assure Lee's function as a back-up power supply to Oconee.
2. Evaluate alternative procedure sequencing which could reduce
the impact of upsets at Lee upon Oconee.
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Oconee Nuclear Station, Unit One 269 . 97 06 00 12 OF 18
3. Review other Safety Related breaker lockout functions and
associated alarm response guides, both at Keowee and Oconee, for
the potential for similar adverse reactions when resetting
lockouts. Revise the alarm response guides as necessary following
this review.
Planned corrective actions 1,2, and 3 are considered NRC
commitment items. No other commitments are included in this
report.
Safety Evaluation
Loss Of Power at Lee:
The event occurred because power was interrupted from the Lee
100 KV line while it was supplying power to Oconee Unit 1. While
this loss was not expected, it was anticipated in the test
procedure contingency plan. Expected alternate power sources
included Keowee Hydro Unit 1 (KH-1) via the underground path, the
Start-up Source via the Oconee Switchyard, or KH2 via the overhead
path. Although KH-1 failed, KH-2 could have been realigned to the
underground path if necessary. Also, Lee or Central could have been
restored as sources.
The event caused a momentary interruption of AC power to Oconee
Unit 1. At the time of the event, the unit was at cold shutdown
with the Reactor Coolant System (RCS) filled, approximately 39 psig
of nitrogen in the Pressurizer, and 100F. The unit had been
shutdown for 6 days and had 7 to 8 MW of decay heat.
Normal decay heat cooling was in service. By procedure, Unit 2
was supplying power to the operating Low Pressure Service Water
Pump so that it would not be affected by dead bus transfers
expected later in the test procedure. The Low Pressure Injection
pump in service was non-load shed, but did require manual action to
restart. This was accomplished with in 1 to 2 minutes. The
temperature of the RCS was observed to increase from 102.5 to 103.0
F.
Under the existing conditions, the time to boil following loss
of decay heat removal was approximately 1 hour, and time to core
uncovery was greater than 8 hours, assuming no heat transfer from
the RCS. The Steam Generators, by procedure requirement, were
partially filled such that
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Oconee Nuclear Station, Unit One 269 97 .06 00 13 OF 18
inventory boil-off would provide additional margin to core
uncovery. In addition, emergency feedwater was available for
alignment from either of the other two Oconee units, and auxiliary
service water was available from the Oconee Stand-by Shutdown
Facility.
A risk calculation was performed for this event and the
estimated core damage probability for this event was approximately
3E-07.
Keowee Unit 1 Inoperability:
The impact of the loss of Lee event on Oconee Units 2 and 3 was
minor. There was no effect on actual operation, but both units were
placed in a 12 hour Limiting Condition for Operation (LCO) until
KH-2 was tested to the overhead path.
The failure to start of the Keowee unit connected to the
underground during a LOCA or LOCA/LOOP is included in the Oconee
licensing basis as a single failure. The Keowee Emergency Start
signal will be initiated by either Engineered Safeguards or Loss of
Switchyard, whichever actually occurs first. The Keowee unit on the
overhead path will start and energize the overhead path. As
occurred in this event, the individual Oconee Unit's Emergency
Power Switching Logic (EPSL) will sense voltage on the overhead
path, and will transfer to that source. In the event of a
LOCA/LOOP, operating LOOP units are expected to close into the
start-up source prior to Main Feeder Bus time out. The LOCA unit
breakers will close approximately five seconds after the path is
energized. (See Attachment 2 Keowee EPSL Sequence of Events.)
In conclusion, in the actual event, power and decay heat removal
were restored promptly. Even in the postulated event that a LOCA or
LOCA/LOOP had occurred on operating units in a similar scenario,
sufficient redundancy existed to assure that emergency power would
have been provided within UFSAR assumed time limits. Therefore, the
health and safety of the public were not affected by this
event.
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OF 18
Attachment 1
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['"INUMBER '] NUMBER
Oconee Nuclear Station, Unit One 269 97 0U6 100 1150F 18
Attachment 2 Page 1 of 4
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Oconee Nuclear Station, Unit One 269 97 06 00 1 6 OF 18
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Oconee Nuclear Station, Unit One 269 97 06 00 170F18
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