Part 21 Report - 1997-670
ACCESSION #: 9705140175
LICENSEE EVENT REPORT (LER)
FACILITY NAME: Quad Cities Unit One PAGE: 1 OF 5
DOCKET NUMBER: 05000254
TITLE: The Residual Heat Removal Service Water System was made
inoperable due to uncertainties related to 4 KV Air
Magne-Blast Horizontal Gas (AMHG) circuit breakers, which
had experienced cracks in the auxiliary switches mounting
channels.
EVENT DATE: 04/09/97 LER #: 97-011-00 REPORT DATE: 04/30/97
OTHER FACILITIES INVOLVED: Quad Cities 2 DOCKET NO: 05000265
OPERATING MODE: 1 POWER LEVEL: 100
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR
SECTION:
50.73(a)(2)(i), 50.73(a)(2)(v)
LICENSEE CONTACT FOR THIS LER:
NAME: Charles Peterson, Regulatory TELEPHONE: (309) 654-2241
Affairs Manager, ext. 3609
COMPONENT FAILURE DESCRIPTION:
CAUSE: B SYSTEM: EB COMPONENT: 52 MANUFACTURER: G168
REPORTABLE NPRDS: N
SUPPLEMENTAL REPORT EXPECTED: NO
ABSTRACT:
The 4 KiloVolt (KV) circuit breakers at buses 13, 14, 23 and 24 were
declared inoperable on 040997 at 1330 hours due to cracks in 4 KV Air
Magne-Blast Horizontal Gas (AMHG)circuit breaker auxiliary switches. The
affected breakers included Residual Heat Removal (RHR) Service Water (SW)
and offsite power distribution breakers. The apparent cause of the event
was a improper manufacturer's switch mounting design. Unit one was shut
down due to Technical Specification 3.8.A. Action 1.d for both RHR SW
subsystems being declared inoperable.
A design change has been completed to install a mounting strap around
auxiliary switches for all affected Unit 14 KV breakers and the Unit 24
KV breaker which provide a path for backup power to Unit 1 from the Unit
2 Reserve Auxiliary Transformer. The same design will be completed for
the remaining Unit 2 breakers prior to start up from Q2R14.
The impact on Safety was minimal in that power would have always been
available to Alternating Current (AC) powered Emergency Core Cooling
(ECCS) Equipment from Diesel Generator Supplied 4 KV Essential Service
buses 13-1, 14-1, 23-1 and 24-1.
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END OF ABSTRACT
TEXT PAGE 2 OF 5
PLANT AND SYSTEM IDENTIFICATION:
General Electric - Boiling Water Reactor - 2511 MWt rated core thermal
power.
EVENT IDENTIFICATION: The Residual Heat Removal Service Water System was
made inoperable due to uncertainties related to 4 KV AMHG breakers, which
had experienced cracks in the auxiliary switches mounting channels.
A. CONDITIONS PRIOR TO EVENT:
Unit: One Event Date: 040997 Event Time: 1330
Reactor Mode: 1 Mode Name: POWER OPERATION Power Level: 100%
POWER OPERATION Mode (1): Mode switch in the Run position with
average reactor coolant temperature at any temperature.
Unit: Two Event Date: 040997 Event Time: 1330
Reactor Mode: 5 Mode Name: REFUELING Power Level: 000%
REFUELING Mode (5): Mode switch in the Shutdown or Refueling
position with average reactor coolant temperature < 140 degrees F
and fuel in the reactor vessel with one or more vessel head closure
bolts less than fully tensioned or with the head removed.
B. EVENT DESCRIPTION:
On 040197 during installation and construction testing of new Sulfur
Hexaflouride (SF6) Air Magne-Blast Horizontal Gas (AMHG) 4 KV
Circuit Breakers [EB] on Unit 2 at Bus 23-1, a breaker auxiliary
switch (52 AUX/UPPER) was found broken loose from the mounting
bracket. These breaker auxiliary switch contacts are used in the
breaker trip circuits, breaker close circuits, breaker anti-pumping
circuit, breaker position indication circuits and for various other
control functions depending on the switchgear cubicle in which the
breaker is installed. These AMHG 4 KV Circuit Breakers are being
installed in the General Electric Air Magne-Blast Horizontal (AMH)
Type Switchgear to replace the existing General Electric AMH 4KV
Circuit Breakers. This was the third broken auxiliary switch found
on AMHG breakers. The first auxiliary switch was found during
factory production testing at Pacific Breaker Systems (PBS) on
021197. The broken switch was replaced at the factory.
The second broken auxiliary switch was found at Quad Cities Station
on 030597 after the breaker had been staged on the turbine floor
prior to installation. Problem Identification Form (PIF) 97-0822
was prepared in response to this.
Additionally, 12 installed, in-service auxiliary switches were found
to be cracked. These switches were installed at buses 23 and 24.
These cracked switches were found during a field walkdown/inspection
on 040897.
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TEXT PAGE 3 OF 5
An operability determination determined that all the breakers on
buses 13, 14, 23 and 24 [EB] were inoperable on 040997 at 1205
hours. A shutdown was commenced at 1330 hours on Unit one due to
Technical Specification 3.8.A. Action 1.d for both Residual Heat
Removal (RHR) [BO] Service Water (SW) [BI] subsystems inoperable.
The 4 KV AMHG breakers installed at buses 13 and 14, which include
all four RHRSW pump breakers and off-site power distribution
breakers, had been determined to be inoperable due to cracked
auxiliary switch mounting channels. Operations made an ENS
notification at 1337 hours due to the Technical Specification
required shutdown per 10CFR50.72.b.1.i.A and the inoperable RHRSW
subsystem per 10CFR50.72.b.2.ii.B.
The breaker auxiliary switch is a subcomponent of the 4 KV breakers.
The affected breakers are all the SF6 AMHG circuit breakers provided
with these switches. These circuit breakers are installed and in
service on Unit 1 at safety related busses 13, 14 and on Unit 2 at
safety related buses 23 and 24. They are presently being installed
on Unit 2 at safety related buses 23-1 and 24-1. Installation is
scheduled for Unit 1 safety related buses 13-1 and 14-1 during the
next Unit I refueling outage (Q1R15). These breakers are also
installed and in service at non-safety Station Black Out (SBO) buses
61 and 71.
On 041197 Golden Gate Switchboard Company issued a Notification of
Potential Defect under the Requirements of 10CFR21.21b.
C. APPARENT CAUSE OF THE EVENT:
The apparent cause of the event was an improper manufacturer's
switch mounting design. There is a design weakness in the auxiliary
switch mounting that manifests itself in cracks in the switch
mounting channels. In extreme cases sufficient cracking can occur
to cause the switch to separate from the mounting plate.
A failure of the auxiliary switch mounting can result in a failure
of these auxiliary contacts to reposition following opening or
closing the breaker which may disable the circuit in which the
switch is wired. For example, if the normal power supply breaker,
Transformer 11 to Bus 14 (Main Feed), spuriously trips open the
Transformer 12 to Bus 14 (Reserve Feed) breaker would not receive
the auto-close signal if the auxiliary contacts fail to reposition.
The manufacturer of the Breakers (Merlin Gerin) is investigating the
cause of the event. The results of this investigation will be
reported per the requirements of 10CFR21.21.
D. SAFETY ANALYSIS OF THE EVENT:
The consequences of this event are considered minimal. There was no
effect on the public or the control room personnel due to this
event.
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During a design basis accident, the RHRSW system functions to
support the RHR system to limit suppression pool temperatures as
required to maintain Emergency Core Cooling Systems (ECCS) pump
suction head. In addition, there are two RHRSW pumps for each RHR
heat exchanger to provide redundancy. During a design basis
accident one RHRSW pump provides adequate cooling water flow to the
associated RHR heat exchanger. No in-service breaker failures
actually occurred at Quad Cities, so the likelihood of losing all
four RHRSW pumps when needed during an event due to breaker failure
from this phenomenon or a random failure is extremely low.
The breakers for the 4 KV Essential Service buses 13-1, 14-1 and
24-1 have not been replaced. The breakers for 4 KV service for 23-1
were in the process of being replaced when the problem was
identified. These four buses supply power to all of the AC
Emergency Core Cooling System (ECCS) Equipment. These buses have
backup power supplied from Emergency Diesel Generators (EDGs). Thus
when the Units were operating, AC power was never in question for
the ECCS equipment as a result of this issue.
E. CORRECTIVE ACTIONS:
Corrective Actions Completed:
1. PIF 97-1276 was written to investigate the cause of the
improper manufacturer's switch mounting design. A level 2
investigation for PIF 97-1276 is in progress.
2. All 4 KV breakers which utilize a Merlin Gerin auxiliary switch
were declared inoperable, and a shutdown on Unit 1 was
completed.
3. Breakers were sent to corporate Materials Engineering Group for
additional testing and the performance of a failure mode
assessment. This testing identified that the breakers could
have performed their design function with cracking present in
the switch mounting plastic and that a design change to install
a strap on the auxiliary switches would be effective.
4. On April 11, 1997, Golden Gate Switchboard Company issued a
"Notification of Potential Defect under the Requirements of
10CFR21.21(b)."
5. A design to install a mounting strap around the rear of the
upper and lower auxiliary switches to ensure they remain
securely fastened to their mounting brackets was performed for
all affected Unit 1 4 KV breakers and the Unit 2 4 KV breaker
which provide a path for backup power from the Unit 2 Reserve
Auxiliary Transformer to Unit 1. Unit 1 was completed by
Design Change Package (DCP) 9700134. The Unit 2 breakers were
completed by DCP 9700141.
6. Operations Department has implemented periodic inspection
requirements to visually check the position indicator flag on
each circuit breaker and weekly log the number of breaker
cycles to ensure that the number of cycles for which the repair
has been tested and qualified is not exceeded.
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TEXT PAGE 5 OF 5
7. Maintenance department has implemented periodic inspection
requirements to visually check the mounting straps on the upper
and lower auxiliary switches.
Corrective Actions to be Completed
1. Complete DCP 9700144 to install a mounting strap for Unit 2
breakers prior to start up from Q2R14. (NTS # 2541809701101)
2. Evaluate the feasibility of extending the qualification of the
mounting strap design by the end of Q1R15 (NTS 2541809701102)
and Q2R15 (NTS 2541809701103 and NTS 2541809701104).
F. PREVIOUS EVENTS:
There have been no previous reportable events regarding failure of
the auxiliary switches for the 4 KV AMHG breakers.
G. COMPONENT FAILURE DATA:
Component Description: 4 KV Breaker Auxiliary Switch
Manufacturer: Merlin Gerin
Breaker Model Number: (Fluarc FG2) AMHG
Part Numbers: Upper switch 7183404A, Lower switch 7183401B
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