Part 21 Report - 1998-241
ACCESSION #: 9803040105
LICENSEE EVENT REPORT (LER)
FACILITY NAME: Clinton Power Station PAGE: 1 OF 6
DOCKET NUMBER: 05000461
TITLE: Division 2 Nuclear Systems Protection System Inverter Not
in Accordance With the Plant's Design Basis Due to
Various Deficiencies
EVENT DATE: 01/27/98 LER #: 98-004-00 REPORT DATE: 02/26/98
OTHER FACILITIES INVOLVED: None DOCKET NO: 05000
OPERATING MODE: 4 POWER LEVEL: 000
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR
SECTION:
50.73(a)(2)(ii)
LICENSEE CONTACT FOR THIS LER:
NAME: M.D. Wagner, System Engineer TELEPHONE: (217) 935-8881
Extension 4071
COMPONENT FAILURE DESCRIPTION:
CAUSE: X SYSTEM: EF COMPONENT: INVT MANUFACTURER: E209
REPORTABLE NPRDS: Y
SUPPLEMENTAL REPORT EXPECTED: YES EXPECTED SUBMISSION DATE: 05/08/98
ABSTRACT:
With the plant in COLD SHUTDOWN technicians identified various
deficiencies in the installed Silicon Controlled Rectifiers (SCR) and
power diodes of the Division 2 Nuclear Systems Protection System (NSPS)
inverter. The compressive force applied to the heatsink clamp hardware
for SCRs and power diodes had been applied and verified incorrectly
causing loose connections. Therefore, the inverter likely would not have
been capable of performing its safety function during a seismic event.
Miscalibration of the inverter lock-up detector assembly resulted in a
loss of the simulated inverter loads during testing under inverter full
load conditions, whereby loss of the simulated bypass power test source
resulted in a reverse transfer of the inverter to the missing bypass
power test source, and a loss of power to the simulated inverter load
bank. These conditions are not in accordance with the plant's design
basis. A cause evaluation for this event has not been completed and
corrective actions have not been identified. However, the Division 2
NSPS inverter SCR and power diode installations have been corrected and
other inverters will be inspected for similar deficiencies and corrected.
This event is also reportable under 10CFR21.
END OF ABSTRACT
TEXT PAGE 2 OF 6
DESCRIPTION OF EVENT
On December 25, 1997, the plant was in Mode 4 (COLD SHUTDOWN) for the six
Outage (RF-6), and reactor (RCT) coolant temperature was being maintained
within a band of 95 to 115 degrees Fahrenheit (F) and pressure was zero
pounds per square inch.
At about 1245 hours, operators in the Main Control Room (MCR) received an
unexpected alarm indicating that the Nuclear Systems Protection System
(NSPS) [EF] inverter [INVT), 1C71-S001B, automatically transferred from
its normal power source to its alternate source. At 1246 hours, an area
operator verified that the Division 2 NSPS inverter was on the alternate
power source. Electrical Maintenance technicians were dispatched to the
inverter, and Maintenance Work Request (MWR) D79429 was initiated to
investigate the automatic transfer.
Four uninterruptible NSPS buses (BU) supply Class 1E 120 Volts
Alternating Current (AC) power to the four logic divisions of the Reactor
Protection System [JC]. An NSPS bus is normally fed via a Direct Current
(DC) to AC inverter supply. The inverter is fed by a 125 Volts DC
divisional battery charger [BYC] with a floating battery [BTRY]. In the
unlikely event of an inverter failure/power loss, the NSPS bus
automatically transfers via a solid state transfer switch, to an
alternate 120 Volts AC source derived from a 480 Volts AC to 120 Volts AC
transformer [XFMR] supply. Also, 120 Volts AC can be supplied to the
Division A and B NSPS buses by manual transfer to an inverter maintenance
bypass feed.
On January 7, 1998, during performance of MWR D79429, technicians
identified several deficiencies in the installed Silicon Controlled
Rectifiers (SCR) and power diodes of the Division 2 NSPS inverter. The
deficiencies included: SCR gate and cathode leads were not tightly
twisted, making the inverter more susceptible to electrical noise from
outside sources; SCRs and power diodes had evidence of arcing on the
conducting surface of the devices, indicating that these devices had
degraded electrical continuity; and excessive Wakefield heat transfer
compound was found applied to the conductive surfaces of the SCRs and
power diodes, creating the potential for hot spots and long term
degradation of the SCRS, power diodes, and the inverter. Technicians
also identified that SCRs had dimples on their conductive surfaces from
the SCR heatsink clamp alignment pin impinging on the SCR surface due to
the SCRs not being properly centered during previous installations of the
SCRs, and additional mechanical defects were noted on SCRs and power
diodes which did not appear to be directly related to the alignment pin
dimples. These conditions affect the conductive surfaces of the
semi-conductors, thereby degrading electrical continuity.
In addition, the compressive force applied to the heatsink clamp hardware
(General Electric Press Pac Clamp Assembly) during previous installations
of SCRs and power diodes had been applied and verified incorrectly using
a torque value. The application of excessive force caused the Press Pac
spring bars to flex beyond their yield point, resulting in inadequate
compressive force applied to the installed SCRs and power diodes. One
semiconductor assembly was installed in an incorrect order, resulting in
the device being out of position with regards to the compression
centering plates. This condition degraded electrical continuity because
the centering pins were not in the proper position.
TEXT PAGE 3 OF 6
Electrical testing of the improperly installed SCRs and power diodes in
the Division 2 NSPS inverter during performance of MWR D79429 indicated
that immediate failure of the these Components was not likely and
immediate operability of the inverter was not affected by the
deficiencies described above. The improper installation of devices
described above can result in increased heating and arcing of the
affected devices and long term degradation of the semi-conductors. The
impact of improper twisting of SCR gate and cathode wires is somewhat
mitigated by plant procedures which control the likely outside sources of
electrical noise. The improper compressive force on SCRs and power
diodes may cause premature degradation of the SCRs, thereby creating the
potential for the inverter to not operate as designed. Condition Report
1-98-01-066 wag initiated to track an investigation land resolution for
these issues.
MWRs were initiated to inspect other potentially affected equipment
including the Division 1 NSPS inverter, 1C71-S001A, the Division 3 NSPS
inverter, 1C71-S001C, the Division 4 NSPS inverter, 1C71-S001D, the A
NSPS Solenoid(RPS) Uninterruptible Power supply (UPS) Inverter,
1C71-S004A, and the B NSPS Solenoid (RPS) UPS Inverter, 1C71-S004B,
On January 12, 1998, during performance of KWR D79429 on the Division 2
inverter, technicians noted that the bolts in the Press Pac spring bar
(General Electric Press Pac Clamp Assembly) used to determine the amount
of force being applied to the SCRs and power diodes felt loose although
the Press Pac spring bar was indicating the proper compressive force.
Investigation of this issue identified that the Press Pac spring bar was
bent, resulting in less than the required compressive force being applied
to the SCRs and power diodes. CR 1-98-01-137 was Initiated to track an
investigation and resolution for these issues. The Operations Shift
Supervisor made resolving this issue a restraint to changing reactor
modes. This issue also potentially affects the Divisions 1, 3, 4, NSPS
inverters, and the A and B NSPS Solenoid (RPS) UPS inverters.
On January 27, 1998, during evaluation of the inadequate compressive
force issue as documented in CR 1-98-01-137, the system engineer
concluded that torquing the General Electric Press Pac Clamp Assembly to
90 to 100 inch pounds caused the Press Pac spring bar to bend beyond its
designed limit, resulting In improper compressive force on the SCRs and
power diodes, and loose connections and arcing on the semi-conductor
surfaces. As a result of the bent Press Pac spring bar and loose
connections, the inverter likely would not have been capable of
performing its intended safety function during a seismic event.
Therefore, the Division 2 NSPS inverter was not in accordance with the
plant's design basis.
On February 1, 1998, during performance testing of the Division 2 NSPS
inverter in accordance with MWR 079429, technicians reported that a loss
of the simulated bypass power test source under inverter full load
conditions (while on a resistive load bank) resulted in a reverse
transfer of the inverter to the bypass power test source (which was
intentionally de-energized as part of the test procedure). The reverse
transfer resulted in a loss of power to the simulated inverter load bank.
This condition is not in accordance with the plant's design basis.
However, this condition did not exist at lower test loads which are more
representative of actual inverter load conditions.
TEXT PAGE 4 OF 6
Investigation of the reverse transfer issue with the inverter supplier
identified that the deficiency is the result of improper calibration of
the lock-up detector adjustment. The improper calibration was performed
in accordance with maintenance procedure CPS 8503.03, "NSPS Inverter
Calibration." CR 1-98-01-455 was initiated to track an investigation and
resolution for these issues. This issue also potentially affects the
Divisions 1, 3, 4, NSPS inverter, and the A and B NSPS Solenoid (RPS) UPS
inverters.
No automatic or manually initiated safety system responses were necessary
to place the plant in a safe and stable condition. This event was not
directly affected by other inoperable equipment or components.
CAUSE OF EVENT
Illinois Power (IP) has determined that incorrect guidance was being used
for installing the Press Pac spring bar and calibrating the inverter
lock-up detector adjustment. A record of coordination between IP and the
inverter supplier, dated August 4, 1988, and contained in vendor manual
X2801-0144, provided the incorrect method of applying compressive force
using a torque value. Recent guidance from the inverter supplier
recommends not using torque as the means for verifying the compressive
force applied to the SCRs and power diodes installed in the heatsinks.
The current supplier-recommended method of applying and verifying
compressive force applied to the SCR and power diode surfaces uses a
gauge and visual indication of a Press Pac spring bar.
IP expects to submit a supplemental report identifying the cause,
corrective action, assessment of the safety consequences and
implications, and similar event information for this event by May 8,
1998.
CORRECTIVE ACTION
CorrectIve action for this event has not been identified, pending
completion of the cause evaluation.
The bent Press Pac spring bar has been replaced and proper compressive
force has been applied to the SCRs and power diodes in the Division 2
NSPS inverter in accordance with MWR D79429. IP will inspect the
Divisions 1, 3, and 4 NSPS inverters and the A and B NSPS Solenoid (RPS)
UPS inverters for deficiencies similar to those described in this report
and correct identified deficiencies, as necessary, to ensure the
equipment is capable of performing their intended safety functions.
ANALYSIS OF EVENT
This event is reportable under the provisions of 10CFR50.73 (a) (2) (ii)
(B) because the Division 2 inverter was not in accordance with the design
basis of the plant
An assessment of the safety consequences and implications associated with
this event has not bean completed but will be provided in a supplement to
this report.
TEXT PAGE 5 OF 6
ADDITIONAL INFORMATION
The Divisions 1, 2, 3, and 4 NSPS inverters are model number INV-752-1-
101, manufactured by Elgar Corporation. The A and B NSPS Solenoid (RPS)
inverters are model number UPS-102-1-189, manufactured by Elgar
Corporation.
Previous similar event information will be provided in a supplement to
this report.
For further information regarding this event, contact M. D. Wagner,
System Engineer, at (217) 935-8881, extension 4071.
IP is providing the following information in accordance with
10CFR21.21(d)(4). Initial notification of this matter will be provided by
facsimile of the letter to the NRC Operations Center in accordance with
10CFR21.21(d)(3) within two days of the date the responsible officer
signs this letter.
(i) Walter G. MacFarland, Chief Nuclear Officer of IP, Clinton
Power Station, Highway 54, 6 Miles East, Clinton, Illinois,
61727, is informing the Nuclear Regulatory Commission of a
condition reportable under the provisions of 10CFR, Part 21.
(ii) The basic component involved in this condition is the safety-
related Division 2 NSPS inverter, manufacturer model number
INV-752-1-101.
(iii) The Division 2 NSPS inverter was supplied to Clinton Power
Station by Elgar Corporation.
(iv) During troubleshooting of the Division 2 NSPS inverter on
January 12, 1998, IP noted that the bolts in the Press Pac
spring bar (General Electric Press Pac Clamp Assembly) used to
determine the amount of force being applied to the SCRs and
power diodes felt loose although the Press Pac spring bar was
indicating the proper compressive force. Investigation of this
issue identified that the Press Pac spring bar was bent,
resulting in less than the required compressive force being
applied to the SCRs and power diodes.
On January 27, 1998, during evaluation of the inadequate
compressive force issue, IP concluded that torquing the General
Electric Press Pac Clamp Assembly to 90 to 100 inch pounds
caused the Press Pac spring bar to flex beyond its yield point,
resulting in inadequate compressive force on the SCRs and power
diodes, and loose connections and arcing on the semi-conductor
surfaces. As a result of the bent Press Pac spring bar and
loose connections, the inverter likely would not have been
capable of performing its intended safety function during a
seismic event. The safety function of the Division 2 NSPS
inverter is to supply uninterruptible NSPS buses with Class 1E
120 Volts AC power for the Division 2 logic of the Reactor
Protection System. Therefore, the Division 2 NSPS inverter was
not in accordance with the plant's design basis.
TEXT PAGE 6 OF 6
Illinois Power has determined that the inverter supplier
provided incorrect guidance for Installing the Press Pac spring
bar. A record of coordination between IP and the inverter
supplier, dated August 4, 1988, and contained in vendor manual
K2801-0144, provided the incorrect method of applying
compressive force using a torque value. Recent guidance from
the inverter supplier recommends not using torque as the means
for verifying the compressive force applied to the
semi-conductor devices installed in the heatsinks. The current
supplier-recommended method of applying and verifying
compressive force applied to, the semi-conductor surfaces uses
visual indication of a Press Pac spring bar.
On February 1, 1998, during performance testing of the Division
2 NSPS inverter in accordance with MWR D79429, technicians
reported that a lose of the simulated bypass power test source
under inverter full load conditions (while on a resistive load
bank) resulted in a reverse transfer of the inverter to the
missing bypass power test source. The reverse transfer
resulted in a lose of power to the simulated inverter load
bank. This condition is not in accordance with the plant's
design basis. However, this condition did not exist at lower
test loads which are more representative of actual inverter
load conditions.
Investigation of the reverse transfer issue with the inverter
supplier identified that the deficiency is the result of
improper calibration of the lock-up detector adjustment. The
improper calibration was performed in accordance with
maintenance procedure CPS 8503.03, "NSPS inverter Calibration."
Illinois Power has determined that the inverter supplier had
not provided proper guidance for calibrating the inverter
lock-up detector adjustment.
(v) The incorrect application and verification methods for applying
compressive force to SCRs and power diodes was identified on
January 7, 1997, and determined to be potentially reportable
under 10CFR21. On January 12, 1993, a bent Press Pac spring
bar was identified on the Division 2 NSPS inverter.
The incorrect calibration of the Division 2 NSPS inverter was
identified on February 1, 1998 and determined to be potentially
reportable under 10CFR21.
(vi) CPS has six safety-related inverters that may be affected by
these deficiencies, including the Division 1 NSPS inverter,
1C71-S001A, Division 2 NSPS inverter, 1C71-S001B, the Division
3 NSPS inverter, 1C71-S001C, the Division 4 NSPS inverter,
1C71-S001D, the A NSPS Solenoid (RPS) UPS Inverter, 1C71-S004A
and the B NSPS Solenoid (RPS) UPS Inverter, 1C71-5004B.
IP is not aware of other facilities that could be affected by
this deficiency.
(vii) Corrective action for this issue has not been identified,
pending completion of the cause evaluation. However, some
currently identified actions are discussed in the LER
CORRECTIVE ACTION section of this report.
(viii) IP has no advice for other purchasers or licensees regarding
this issue.
ATTACHMENT TO 9803040105 PAGE 1 OF 1
POWER REACTOR EVENT NUMBER: 33800
FACILITY: CLINTON REGION: 3 NOTIFICATION DATE: 02/26/98
UNIT: [1] [ ] [ ] STATE: IL NOTIFICATION TIME: 16:18 [ET]
RX TYPE: [1] GE-6 EVENT DATE: 02/26/98
EVENT TIME: 16:18 [CST)
NRC NOTIFIED BY: R. FRANTZ LAST UPDATE DATE: 02/26/98
HQ OPS OFFICER: JOHN MacKINNON
NOTIFICATIONS
EMERGENCY CLASS: NOT APPLICABLE
10 CFR SECTION: JEFF WRIGHT RDO
CDEG 21.21(c)(3)(i) DEFECTS/NONCOMPLIANCE
VERN HODGE (PCEB) NRR
UNIT SCRAM CODE RX CRIT INIT PWR INIT RX MODE
1 N N 0 COLD SHUTDOWN
CURR PWR CURR RX MODE
0 COLD SHUTDOWN
EVENT TEXT
DIVISION 2 NUCLEAR SYSTEMS PROTECTION SYSTEM INVERTER NOT IN
ACCORDANCE
WITH THE PLANT'S DESIGN BASIS DUE TO VARIOUS DEFICIENCIES.
WITH THE PLANT IN COLD SHUTDOWN, PLANT TECHNICIANS IDENTIFIED
VARIOUS
DEFICIENCIES IN THE INSTALLED SILICON CONTROLLED RECTIFIERS (SCR) AND
POWER DIODES OF THE DIVISION 2 NUCLEAR SYSTEMS PROTECTION SYSTEM
(NSPS)
INVERTER. THE COMPRESSIVE FORCE APPLIED TO THE HEAT SINK CLAMP
HARDWARE
FOR SCRs AND POWER DIODES HAD BEEN APPLIED AND VERIFIED INCORRECTLY
CAUSING LOOSE CONNECTIONS. THEREFORE, THE INVERTER LIKELY WOULD
NOT HAVE
BEEN CAPABLE OF PERFORMING ITS SAFETY FUNCTION DURING A SEISMIC
EVENT.
MISCALIBRATION OF THE INVERTER LOCK-UP DETECTOR ASSEMBLY RESULTED
IN A
LOSS OF THE SIMULATED INVERTER LOADS DURING TESTING UNDER INVERTER
FULL
LOAD CONDITIONS, WHEREBY LOSS OF THE SIMULATED BYPASS POWER TEST
SOURCE
RESULTED IN A REVERSE TRANSFER OF THE INVERTER TO THE MISSING BYPASS
POWER TEST SOURCE, AND A LOSS OF POWER TO THE SIMULATED INVERTER
LOAD
BANK. THESE CONDITIONS ARE NOT IN ACCORDANCE WITH THE PLANT'S
DESIGN
BASIS. A CAUSE EVALUATION FOR THIS EVENT HAS NOT BEEN COMPLETED AND
CORRECTIVE ACTIONS HAVE NOT BEEN IDENTIFIED. HOWEVER, THE DIVISION 2
NSPS INVERTER SCR AND POWER DIODE INSTALLATION HAVE BEEN CORRECTED
AND
OTHER INVERTERS WILL BE INSPECTED FOR SIMILAR DEFICIENCIES AND
CORRECTED.
*** END OF DOCUMENT ***
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