ML20127N234

Interim Part 21 Rept Re Defect in GE RMS-9 Trip Devices W/ Instantaneous Trip Function.Initially Reported on 921027. Util Formally Discontinued Installation of Defective Devices & Investigating Replacement of Units W/Ge

ML20127N234
Person / Time
Site:	Browns Ferry
Issue date:	11/25/1992
From:	Zeringue O TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-92 NUDOCS 9212010101
Download: ML20127N234 (7)

Text

. _ _ - _ .

l IUA t.nmee vwy um, aw om anam. acas meean eco3 c.J m 'zm ngue

. vte awnen. h,3 rm n.saown

( *

' November 25, 1992 t

U.S. Nuclear Regulatory Comrnission ,

- ATIN t ' Document Control Desk l

Washington, D.C. 2055$

Centlemen:

l In the Matter of ) Doc!:et Hoc 50-259 l Tennesset Valley Authority ). 50-260 l 50-296-1 BROWNS FERRY NUCLEAR PLANT (BFN)' - DEFECT OR FAILURE TO COMPLY - RMS -9 TRIP DEVICES WITH INSTANTANEOUS TRIP.FIINCTION-Enclosura 1 providea written notification,.in accordance with-10 CPR 21.21(c)(3)(ii), of a defect or failure to comply cor.cerning, RMS-9 "

trip devices with instantaneous trip functions!, Init-lal notific/ ion-required by 10 CFR 21.21(c)(3)(1) was made by facsimile to;the NRC '

Operations Center on October 27, 1902, e

A summary Tist of cou:mitraents contained -in: this letter is provided in '

l -. Enclosure 2. If you have any questions, . please telephene C. D. Pierce, L Interim Manager of Site Licensing, at' (205) 729-7566. -

Sincerely, d

O!' JI Zeringue 1 Enclosures

cci See page 2 -

300170 - ..

-,9212010101'921125 pm : ADOCK'05000259-> h. Pj j .

- eas  ;

bp. .

t

4 2

U.S. Muclear Regulatory Ccamission November 25, 1992 Enclosures

cc (Enclosures):

NRC Resident Inspector Brovna Ferry Nuclear Plant j Route 12, Box 637 Athens, Alabana 35611 Mr. Thierry M. Ross, Project hanuger l U.S. Nuclear Regulatcry Comminslon '

One White Filnt, North

-11555 Rockville Pika Rockville, Maryland 20852 Mr. B. A. Wilson, Pro. ject Chief U.S. Nuclear Regulatory Commission i Region II ,

, 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 I

i ,

i 4

h O

t l

4 l

l y , s v ~

l i

l Euclosure 1 Page 1 of 4 l

Tennessee Valley Authority d

lirewns Ferry Nuclear Plant (BFNP) 10CFR21 Report 1015-9 Trip Devices With Instantaneous Trip Functiou

l. Name and address of the individual (or individuals) informing the Commission.

O. J. Zeringue, Browns Ferry Site Vice President Browns Ferry Nuclear Plant Browns Ferry and Nuclear Plant Road

, Athens, Alabama 35611

2. Basic component supplied which fails to comply or contains a defect.

~

General Electric RMS-9 Trip Device with Instantaneous Trip function. This device is used as the trip device for low voltage power circuit brea'kers (specifically AK-15 and AK-25 breakers at BFNP).

3. The firm constructing or supplying the basic component which falls to comply or contains a defect,

, General Electric (GE) Company

4. Nature of the defect, or failure to comply, nud the safety hazard created, or could be created.

l Malurp_qlthsulefect ur {gihggArmgJy The RMS-9 trip device was certi6ed by GE as a suitable replacement for the EC trip units that were originally installed in GE AK circuit breakers. Per GE, to prevent spurio'is trips, a hold-off circuit ensures that the fault condition persists for a sufficient duration to insure that a tiip is wananted. This delay is approxunately 300 microseconds. Thus, a fault current that exceeds the instantaneous trip function

pickup for a time datation in excess of 300 microseconds should be required to initiate an instantaneous trip of the breaker.

J

\

Enclosure 1 Page 2 of 4 :

The 480 solt distribution system at BFNP is ungrounded and has experienced -

extremely short duration current transients that resulted in the RMS-9 unit initiating a breaker trip. Subsequent testing, performed by TVA as part of an investigation into the cause of spurious breaker trips, demonstrated that the RMS-9 unit will trip in response to pulse widths of substantially less duration than 300 microseconds if the current value is sufficiently above the instantaneous setpoint.

TVA is in the process of converting GE AK breakers with EC trip devices to RMS-9 tnp devices and has installed a limited number of RMS-9 trip devices with instantaneous trip function in the 480 volt distribution system for Units 1 and 3.

Currently, there are 6 installed in safety related equipment and 4 installed in non safety related equipment. TVA also planned to install the RMS-9 units with instantaneous trip function on GE AK breakers throughout the 480 volt distribution system for all three units.

Browns Ferry also uses a limited number (12 total,4 per unit) of molded case circuit brea.kers equipped with RMS-9 trip devices with instantaneous function on its 208/12.0 volt system. This is a grounded system and the trip device application does not create a safety concern.

liYahlation of Safety Hazard Created RMS-9 trip devices with instantaneous trip function were installed in two circuit breakers in the circuits for control air compressor A and D and four circuit breakers in the circuits for Instrumentation and Control (I&C) buses for Units I and 3. The operability of these circuits were evaluated and determined to have no adverse effect on plant operation. Specifically, should a single failure cause the loss of an air compressor or an I&C bus there :is no safety related impact. If the I&C circuit breakers experience a spurious trip, the bus will transfer to its alternate source.

Since Units 1 and 3 are out of service, the Units 1 and 3 areas do not experience harsh environments during a Unit 2 accident. Thus, the most likely common-mode failure initiator (accident environmentally induced faults) is not applicable. Based upon a transfer to its alternate source and the lack of a common-mode failure initiator to create faults or tnmsients of sufficient magnitude to initiate tripping (instantaneous setting are 2250 amp.), there is no reason to believe that the Unit I and 3 I&C bus breakers will not support Unit '2 operation and safe-shutdown.

Evaluation of Pq,ential t Safety %7ard Created l The assumption that a common mode initiator exists, such as environmentally induced failures resulting from a design basis accident, results in postulation of a more widespread condition. This postulated condition could result in the possibility of both _ l non safety related and safety related 480 volt buses for one or more units experiencing this disturbance. Thus, the postulation of a loss of multiple unit 480 1

I

Enclosure 1 Page 3 of 4 volt shutdown board breakers, because of spurious tripping, could result in a loss of 120 volt I&C power as well as the 460 volt motors that are fed from the 480 volt shutdown boards. This results in a design basis accident in one unit potentially causing the loss of significant safety related equipment for all three units.

Completion of the conversion to RMS-9 trip devices would have subjected safety related and non safety related low voltage switchgear breakers to potential tripping in the event of a disturbance such as that experienced at BFNP. Thus, the potential for

, tripping of these breaken was considered assuming trat dther a common mode initiator existed or did not c ist. While the postulated event described above may be possible, the actual simultaneous occurrence of the disturbance on more than one I&C bus regulating transformer is not believed to be probable, Without a common mode initiator, the simultaneous occurrence of this type of

~

disturbance occurring on more than one 480 volt I&C ous regulating transformer is not considered credible. Exclusion of a common-mode initiator restricts the potential risk of spurious circuit breaker trips to one transformer bus. This results in a wor:;t case condition of a single failure causing the loss of one transformer bus in addition to the spurious tripping. This condition could result in the loss of one division's 480 volt shutdown board and the spurious tripping of the motors and I&C bus transformer for the redundant division.

5. The date on which the infonnation of such defect or failure to comply was obtained.

TVA identified the RMS-9 trip devices with instantaneous trip function as a potential

deviation when laboratory testing on October 16,1992 demonstrated that the devices would trip in response to a 100 microsecond pulse width if the current value is sufficiently above the instantaneous trip setpoint. TVA concluded on October 22, 1992, that the condition was a defect. The Browns Ferry Vice President was informed of the defect on October 26,1992. Initial notification by facsimile was made to the NRC Operations Center on October 27,1992.

6. The number of identical components in use or supplied for 480 volt distribution system.

There were 39 RMS-9 conversion kits with instantaneous trip functions purchased for use at BFNP. Physical plant walkdowns showed that six of these conversion kits are installed in safety related equipment and four are installed in non safety related equipment. In addition, one was sent to General Electric for testing, one is in the electrical shop, and 23 are in the warehouse. TVA has concluded that four RMS-9 trip devices were discarded. This conclusion is based on a review of work documents and the results of the physical plant walkdowns. Also, the physical plant walkdowns showed that these four conversion kits were not installed in safety related locations in

4 Enclosure 1 Page 4 of 4 the plant. However, TVA has not been able to confirm they were discarded and has

! initiated a corrective action document to track resolution of this concern. In addition, TVA contracted General Electric to refurbish 32 breakers and install the RMS-9 trip cr.it with instantaneous functions in place of the original EC trip unit. Of these, twenty-one are in the electrical shop, nine are in the warehouse, and two are still at General Electric.

7. Location of Installed Components:

The six installed in safety related equipment are located as follows:

480V Shutdown Board 1 A (compt. 3D - Unit 1 I&C Bus ai 480V Shutdown Board 1 A (compt. 5A - control air compressor A) 480V Shutdown Board IB (compt. 3D - Unit 1 I&C Bus B) 480V Shutdown Board 2A (compt. 5 A - control air compressor D) 480V Shutdown Board 3A (compt. 28 - Unit 3 I&C Bus A) 480V Sbutdown Board 3B (compt. 5B - Unit 3 I&C Bus B).

The three installed in non safety related equipment are located as follows:

480V Common Board 3, Compartment 9D i 480V Common Board 3, Compartment 4B 480V Common Board 1, Compartment 3C 480V Common Board 1, Compartment 7C 4

8. The corrective action planned or being taken, the responsible organization, and the schedule for completion of planned actions.

TVA formally discontinued installation of RMS-9 trip devices with instantaneous trip function on October 5,1992. TVA is investigating the pc,ssibility of GE providing trip units that are less se.asitive to transients or short duration current pulses. This could possibly be accomplished with modified RMS-9 trip units or a commitment to support the continued use of the EC device which is an obsolete item.

9. Any advice that has been given, is being, or may be given, about the defect.

TVA has no advice to offer regarding the use of the RMS-9 trip device with instantaneous trip function.

4

o .

Enclosure 2

SUMMARY

OF COMMITMENTS TVA is investigating the possibility of GE providing trip units that are less sensitive to transients or short duration current pulses. TVA expects to complete this investigation by February 26,1992, t

t

.