United States Nuclear Regulatory Commission - Protecting People and the Environment


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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