Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9512260101
Illinois Power Company
Clinton Power Station
P O Box 678
Clinton, IL 61727
Tel 217 935-8881
ILLINOIS
POWER U-602532
L16-95(12-20)LP
4F.140
JGC-536-95
December 20, 1995
Docket No. 50-461 10CFR21.21
Document Control Desk
Nuclear Regulatory Commission
Washington, D.C. 20555
Subject: 10CFR21 Final Report 21-95-018, Asea Brown
Boveri/ITE/Gould/Brown Boveri Power Shield
Type 33-13 Solid State Trip Devise Failures
Dear Sir:
Illinois Power (IP) issued 10CFR21 Interim Report 21-95-018 on
October 6, 1995, via letter U 602502, to notify the Nuclear Regulatory
Commission (NRC) of a potentially reportable condition discovered at
Clinton Power Station (CPS). The issue involves the failure of Power
Shield Type SS-13 solid state trip devices (SSTDs) manufactured by Asea
Brown Boveri (ABB)/ITE/Gould/Brown Boveri. At the time of the October 6,
1995 report, IP had not completed the reportability evaluation for this
issue. The final report of this issue is provided herein.
On August 7, 1995, during an attempt to shift the Control Room
Heating, Ventilating and Air Conditioning (VC) system operation from the
A train to the B train, the B train return air fan would not start. An
investigation of the failure to start found the fan's circuit breaker,
0AP06E5D, in a tripped condition. Upon discovery of the tripped breaker,
IP staff reset the circuit breaker and attempted to start the fan but the
breaker tripped again, The breaker was replaced with a spare breaker, and
the fan started and operated satisfactorily. Testing of the deficient
breaker on August 8, 1995, identified that its Power Shield Type SS-13
SSTD, serial number 45779, was causing the breaker to trip. The device
was returned to the supplier for further evaluation.
On August 10, 1995, IP determined that the deficient device was a
condition potentially reportable under the provisions of 10CFR21.
U-602532
Page 2
On August 21, 1995, IP identified another potentially deficient
Power Shield Type SS-13 SSTD. This device, serial number 45778, was
installed in the B Switchgear Heat Removal (VX) system condensing unit
motor circuit breaker 1AP12F6D. The trip device in the VX system
exhibited symptoms similar to those of the VC system device discussed
above. This device was also returned to the supplier for further
evaluation.
The investigation of the two deficient Type SS-13 SSTDs identified
broken solder connections on circuit cord edge connectors. Since the
serial numbers of the two devices were sequential, the broken solder
connection problem was considered potentially generic. Therefore, on
October 20, 1995, the scope of potentially affected devices was expanded
to include all Power Shield Type SS-13 SSTDs. An additional Type SS-13
device problem was identified in a non-Class 1E breaker application.
On October 31, 1995, the scope of potentially affected devices was
expanded to include Type SS-14 solid state trip devices. Although CPS had
not experienced failures of this type of device the design of the circuit
card edge connection is identical for the Type SS-13 and SS-14 SSTDs.
On November 20, 1995, ABB submitted a report to the NRC under the
provisions of 10CFR21 discussing the results of their evaluation of the
devices returned to them by CPS. The report identifies that defective
solder connections in the Power Shield solid state trip devices caused
the false trips of the CPS circuit breakers. The report identifies the
cause of the defective solder connections and provides recommended
actions and repair instructions. The report recommends that purchasers
inspect all Power Shield SS series trip units (includes Types SS-13 and
SS-14) having serial numbers less than 80,000 for defective solder
connections.
IP provides the following information in accordance with 10CFR21.21
(c)(4). Initial notification of this matter will be provided by
facsimile of this letter to the NRC Operations Center in accordance with
10CFR21.21(c)(3) on the date this letter is signed by the responsible
officer.
(i) J. G. Cook, Senior Vice President of IP, Clinton Power Station,
Post Office Box 678, Clinton, Illinois, 61727, is the
responsible officer notifying the NRC of a condition reportable
under the provisions of 10CFR Part 21 by means of this report.
(ii) The basic components involved in this condition are Power
Shield solid state trip devices, Type SS-13, manufacturer part
number 609901-T012. The Type SS-13 SSTDs provide electrical
overcurrent protection of motor circuit breaker loads.
(iii) The SSTDs were manufactured under the following company names:
Asea Brown Boveri, ITE, Gould, and Brown Boveri.
U-602532
Page 3
(iv) The two Type SS-13 SSTDs installed in the VC and VX systems
were electrically tested and inspected by ABB. Testing of the
VC system unit identified an intermittent output signal that
would cause the breaker to false trip. During disassembly and
inspection of the unit, a 360-degree break was identified in
the solder connection of a pin on the printed circuit board
edge connector located on the control board, The pin connects
the anode of diode D-205 to a terminal connected to the R-11
power supply external load resistor. Opening this circuit
causes the device to trip. The edge connector is a Molex right
angle type 2145 with gold plated brass terminals.
Testing of the VX system device did not identify any
malfunctions. During disassembly and inspection of the device
a 360-degree break was identified in the same solder connection
as discussed above for the VC system device. In addition, a
second pin showed some partial signs of cracking but less than
360 degrees.
ABB identified that the root cause of the broken solder
connections was grain coarsening and copper diffusion
embrittlement of the solder fillets. The embrittlement aided
fatigue cracks brought on by mechanical and thermal stress.
IP has concluded that the deficiency in the Type SS-13 solid
state trip devices could have created a substantial safety
hazard if it had gone uncorrected. The safety function of the
VC system is to maintain a habitable environment and ensure the
operability of all components in the main control room under
all operating and accident conditions. The VC system is
comprised of two redundant trains. A failure of the VC system
B train return air fan due to the deficient Type SS-13 SSTD,
combined with a single failure in the VC system A train, could
prevent the VC system from performing its safety function.
Loss of safety function is considered to be a substantial
safety hazard.
(v) The Type SS-13 solid state trip device in the VC system was
identified as potentially deficient on August 8, 1995. IP
determined that the trip device was potentially reportable
under the provisions of 10CFR, Part 21 on August 10, 1995.
(vi) Type SS-13 solid state trip devices are typically installed on
auxiliary power 480-volt circuit breakers used for motor
control at CPS. CPS has 12 Class 1E Type SS-13 SSTDs installed
in safety-related circuit breakers and 9 Class 1E Type SS-13
SSTDs installed in spare safety-related breakers. The
applications of these breakers include the following heating,
ventilating, and air conditioning (HVAC) systems: Switchgear
Heat Removal, Diesel Generator Room HVAC, Drywell Cooling HVAC,
and Control Room HVAC. In addition, CPS has 22 Class 1E Type
SS-13 SSTDs in stores.
U-602532
Page 4
(vii) IP inspected and reworked, as needed, the 12 Type SS-13 SSTDs
installed in safety-related breakers in accordance with
instructions provided by ABB.
Eight of the 9 Type SS-13 SSTDs installed in spare breakers
have been returned to ABB with their breakers and will be
replaced with new units during refurbishment of the breakers.
The remaining one Type SS-13 SSTD installed in a spare breaker
is currently scheduled to be replaced during breaker
refurbishment by ABB in 1996.
IP inspected and reworked, as needed, the 22 Class 1E Type SS-
13 SSTDs located in stores.
Failures of Power Shield Type SS-14 solid state trip devices
have not occurred at CPS to date. However, CPS has developed a
plan to inspect the solder connections and rework or replace
the Class 1E Type SS-14 SSTDs as needed.
(viii) IP's advice to other licensees and purchasers of Type SS-13
SSTDs is that false trips of breakers containing Type SS-13
SSTDs should be considered to be symptomatic of the deficiency
described herein.
ABB submitted a report to the NRC under 10CFR21 on November 20,
1995. That report indicates that ABB will notify all
purchasers about the issue.
Additional information about the CPS issue may be obtained by
contacting D. G. Lukach, system engineer, at (217) 935-8881, extension
3952.
Sincerely yours,
J. G. Cook
Senior Vice President
RSF/csm
cc: NRC Clinton Licensing Project Manager
NRC Resident Office, V-690
Regional Administrator, Region III, USNRC
Illinois Department of Nuclear Safety
INPO Records Center
Asea Brown Boveri
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