U-602532, Final Part 21 Rept 21-95-018 Re Failure of Power Shield Type SS-13 Solid State Trip Devices (Sstd) Mfg by Asea Brown Boveri,Ite,Gould & Brown Boveri.Util Inspected & Reworked,As needed,12 Type SS-13 Sstds in safety-related Breakers

Final Part 21 Rept 21-95-018 Re Failure of Power Shield Type SS-13 Solid State Trip Devices (Sstd) Mfg by Asea Brown Boveri,Ite,Gould & Brown Boveri.Util Inspected & Reworked,As needed,12 Type SS-13 Sstds in safety-related Breakers

ML20095H590
Person / Time
Site:	Clinton
Issue date:	12/20/1995
From:	Jackie Cook ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-95 JGC-536-95, U-602532, NUDOCS 9512260101
Download: ML20095H590 (4)

Text

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l Docket No. 50-461 10CFR21.21 Document Control Desk l Nuclear Regulatory Committinn hhington-D C. 20555 Subjee.t: 10CFR21 Final Report 21-95 018: Asea Brown Boveri/ITFJGould/ Brown Boveri Power Shield ,

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Dear Sir:

1 Illinois Power (IP) issued 10CFR21 Interim Report 21-95 018 on October 6, 1995, via lotter U 6o2502, to notify the Nuclear Regulatory Commission (NRC) of a I

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)/ITFJGould/ Brown Boveri. At the time of the October 6,1995 report, IP had not completed the reportability evaluation for this i n. .e ri c n . t y,uit or thi3133uc.13 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 bicakei, IP stafric3ct 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.

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Page 2 On August 21,1993, IF identitled another potentially deficient Power Shield Type SS-13 SSTD. This device, serial number 45778, was installed in the B Switchgear Heat

- Rosuuval (V7C) ayatsm eendeneias unit motor aircuit breaker 1 A D1?FAr) The trip device

'in the VX system exhibited symptoms similar to those of the VC system device discussed ubuve This device was also retumed to the supplier for further evaluation.

The invcatisation of the two donwi.ut Type SS-13 SSTDs identified brnlmn Anlder eenneetica. an alce,,it aard adse ennnectors. Since the serial numbert of the two devices

[-

were sequential, the broken solder connection problem was considered potentially scucaiv.

Therefore, on October 20,1995, the scope of potentially affected devices was expanded to include all Power Shield Type SS-13 SSTDs. An additiorial Type SS-13 device problem was identified in a non-Class th breaker apptication.

On October 31,1995, the scope of potentially affected devices was expanded to include Type _SR-14xlid state trip devices. Although CPS had not experienced failures of this type ordevice the uc>lgn ur the oissuit ved cup wnucction la idendw I n,. die Typ.e SS 13 and SS 14 SSTDs.

On November 20,1995, ABB submitted a report to the NRC under the provisions of 10CFR?) dicrutsing 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 dcfcctive solder connections and provideo recommended setions and repair instructions. The report recommends that purchasers inspect all Power Shield SS series tilp units (luuludes Types 33-13 and SS-14) having oorial numbers less than 80,00n for defective solder conncctions.

IP provides the following information in accordance witn lucric t.z1(c)(*).

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 respontible officer.

, (i) J. G. Cook, Senior Vice President ofIP, Clinton Power Station, Post Office Box '

678, Clinton, Illinois, 61727, is she responsible officer notifying the NRC of a condition report ble under the provisiona_of 10CDU, Dart ?1, by rtseant of this report.

(ii) The basic components involved in this condition are Power Shield solid state trip devisca, Type SG 13, manutacturce part number ovv901-Tott True Typ. 39 11 SSTDs provide electrical overcurrent protection of motor circuit breaker loadsc --

(111)

The SSTDs welc nianufautuacd unde,r the followin5 company names: Ames Drown Boveri. ITE, Gould, and istown isovert.

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. U-602532 Page 3 (iv)- The two Type SS-13 SSTDs installed in the VC and VX systems were electrically tested and inspected by ABD. 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 externalload 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 tecnnd pin shnwed enme partial signe of cracking, but le<< than 'MO 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 ifit 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.

i  ;

(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 lE Type SS-13 SSTDs installed in safety-related circuit breakers and 9 Class IE Type l 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 Remgval, Diesel Generator Room HVAC, Drywell Cooling HVAC, and Control Room HVAC. In addition, CPS has 22 Class lE Type SS 13 SSTDs in stores.

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. 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 IE 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 IE Type SS-14 SSTDs as needed.

(viii) IP's advice to other licensees and purchasers ofType SS-13 SSTDs is that false trips of breakers containing Type SS-13 SSTDs should be considered to L 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, t

. Cook Senior Vice President RSF/csm cc: NRC Clinton Licensing Project Manager NRC Resident Office, V-690 l Regional Administrator, Region III, USNRC  !

Illinois Department of Nuclear Safety INPO Records Center Asea Brown Boveri e