United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9509280075

                                        Illinois Power Company
                                        Clinton Power Station
                                        P.O. Box 678
                                        Clinton, IL  61727
                                        Tel 217 935-5623
                                        Fax 217 935-4632

ILLINOIS                                John G. Cook
  POWER                                 Vice President
                                             U-602497
                                             L16-95(09-26)LP
                                             4F.140
                                             JGC-397-95
                                             September 26, 1995
Docket No. 50-461

Document Control Desk
Nuclear Regulatory Commission
Washington, D.C. 20555

Subject:       10CFR21 Final Report 21-95-010: Elgar
               Inverter PWM Drive Logic Card (J4) Failure

Dear Sir:

     On March 24, 1995, a new PWM drive logic card (J4) was installed in
the Division 2 Nuclear Systems Protection System (NSPS) inverter at
Clinton Power Station (CPS).  The new card failed after four to six hours
of operation during calibration of the inverter.  At the time of the
failure, the inverter was out of service to replace the logic card with
this revised card in accordance with a scheduled maintenance activity.

     On May 22, 1995, Illinois Power (IP) issued 10CFR21 Interim Report
21-95-010: Elgar Inverter PWM Drive Logic Card (J4) Failure, (IP letter
U-602446), to notify the NRC that IP was evaluating logic card failures
in accordance with the provisions of 10CFR21.  At the time the report was
issued, IP did not know the cause of the card failure, but had returned
the logic card to the supplier for failure analysis.

     On July 12, 1995, IP issued a follow-up letter to the NRC (IP letter
U-602466) to report that the evaluation of the J4 logic card failure was
not complete.  Testing performed by Elgar Corporation at their facilities
did not identify any manufacturing or design deficiencies in the logic
cards; however, since the cards did fail in the CPS inverter, Elgar
performed additional testing of the cards on site (at CPS).  At the time
the follow-up letter was issued, Elgar had not completed their evaluation
of the on-site test results.

     Since the July 12 submittal, Elgar completed their evaluation of the
data obtained from the on-site testing and determined the testing results
were inconclusive.  Elgar had planned to perform additional testing of
the cards on site using the installed inverters; however, IP evaluated
the risk to the operability of the inverter and determined that testing
will not be permitted during plant operation.  IP has determined that the
next potential window of opportunity for using the installed inverters
for testing is the sixth refueling outage (RF-6), currently scheduled to
begin in October, 1996.  However, at this

                                                  U-602497
                                                  Page 2

time, IP has not made a commitment to allow testing during RF-6.  The CPS
inverters have had other continuing problems and IP is in the process of
evaluating their reliability.  Therefore, IP is pursuing two success
paths for the inverters, one being to replace the inverters, the other
being to correct the continuing material problems of the existing
inverters.

     IP has concluded that the failure of the logic cards is reportable
under the provisions of 10CFR21 and considers this document to be the
final report on this subject.  Elgar Corporation should be contacted for
further information regarding the cause of the logic card failures.

     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, Vice President of Illinois Power, Clinton Power
          Station, Post Office Box 678, Clinton, Illinois, 61727, is the
          responsible officer informing the Nuclear Regulatory Commission
          (NRC) of a condition reportable under the provisions of 10CFR,
          Part 21, by means of this report.

(ii)      The basic component involved in this condition is a PWM drive
          logic card, part number 642-108-40, revision F.  The logic card
          was installed in the Division 2 NSPS inverter.  The inverter
          provides 120 volts alternating current (AC) uninterruptible
          power to loads such as NSPS logic power, neutron monitoring,
          process radiation monitoring, portions of the leak detection
          system, nuclear steam supply shutoff system valves and loss of
          coolant accident bypass relays during all modes of operation
          including abnormal and accident conditions.  The logic card
          provides control signals to the SCR (silicon controlled
          rectifier) drives.  The same logic card part can be used in the
          Divisions 1, 2, 3, and 4 NSPS inverters but the revised card
          was never installed in the Divisions 3 and 4 inverters at CPS.

(iii)     The logic card was manufactured by Elgar Corporation and
          supplied to CPS by Elgar Corporation/General Electric.

(iv)      IP installed the logic card in the inverter during a scheduled
          maintenance activity.  During calibration of the inverter, the
          logic card operated for four to six hours and then failed for
          no known reason.

          The failure of the logic card causes the inverter to shut down.
          When this occurs, the inverter loads are transferred to the
          alternate AC source of power.  During the failure of the logic
          card at CPS, the inverter was out of service for scheduled
          maintenance and not required to be operable.  However, if the
          logic card had failed

                                                       U-602497
                                                       Page 3

          during a loss of offsite power (LOOP) condition, the NSPS loads
          would be transferred to the alternate AC power source which may
          not be available due to the LOOP condition and the NSPS loads
          would lose power.

(v)       The logic card failure was discovered on March 24, 1995.  On
          March 25, 1995, IP determined that the failure was potentially
          reportable under the provisions of 10CFR, Part 21.

(vi)      IP received one other logic card part number 642-108-40,
          revision F.  This logic card was identified as deficient when
          it was initially installed in the Division 1 NSPS inverter
          during a similar maintenance activity.  Following installation
          of the card, the Division 1 NSPS inverter would not operate,
          that is, the inverter SCR drive section operation would not
          function.  The failure of the card installed in the Division 1
          NSPS inverter was obvious and could not have gone undetected
          since the inverter could not be declared operable if the SCR
          drives were inoperable.  IP has no information about logic
          cards that may have been supplied to other purchasers.

(vii)     The logic card that failed in the Division 1 NSPS inverter has
          been replaced with the original logic card, part number 642-
          108-40, revision A.  The logic card that failed in the Division
          2 NSPS inverter has been replaced with a logic card part number
          642-108-40, revision E.  Both logic cards that failed have been
          returned to Elgar Corporation for failure analysis.  IP will
          continue to track this issue in accordance with Condition
          Report 1-95-03-113.

(viii)    IP has no advice to offer other purchasers or licensees about
          this issue at this time.  Additional information about this
          issue may be obtained by contacting D. G. Lukach, system
          engineer, at (217) 935-8881, extension 3952.

                                   Sincerely yours,

                                   J. G. Cook
                                   Vice President

RSF/csm

cc:       NRC Clinton Licensing Project Manager
          NRC Resident Office, V-690
          Regional Administrator, Region III, USNRC
          INPO Records Center
          Illinois Department of Nuclear Safety
          Elgar Corporation

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