United States Nuclear Regulatory Commission - Protecting People and the Environment


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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