ML20055F922

Safety Evaluation Supporting Util Responses to NRC Bulletin 88-010 Re Molded Case Circuit Breaker Replacement

ML20055F922
Person / Time
Site:	Quad Cities
Issue date:	07/17/1990
From:	NRC
To:
Shared Package
ML20055F920	List: ML20055F919 ML20055F922
References
IEB-88-010, IEB-88-10, NUDOCS 9007190368
Download: ML20055F922 (3)

Text

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. NUCLEAR REGULATORY COMMISSION WASHING 1ON, D. C. 2f*55 7 Tj

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J SAFETY EVALUATION REPORT

, QUAD CITIES UNIT I MOLDED-CASE CIRCUIT BREAKER REPLACEMENT INTRODUCTION During the last Quad Cities Unit I refueling outage, four molded-case cir-cuit breakers failed during surveillance testing. For three of these, the plastic handle broke during manual cycling. The fourth failed when one pole of the breaker tripped at 75 percent of tie instantaneous trip setting (9 times the motor nameplate full load current).

-By letters to the NRC dated November 20, 1989 and November 29, 1989, the licensee descrited the failures and formally informed the NRC that the only replacement breakers available were restricted from use by Action 7 of NRC Bulletin 88-10 in that they were not traceable to the circuit breaker manu-facturer. The licensee requested concurrence to deviate from Action 7 of the Bulletin for these breakers because suitable replacements could not be obtained until late December 1989 or January 1990. The licensee referred to telecons on November 20 and November 22, 1989 in which preliminary approval was granted by the NRC for use of the replacement breakers pending a formal review by the NRC.

The licensee has tested the four replacement breakers in accordance with NRC Bulletin 88-10 including the following tests:

- mechanical test

- millivolt drop test.

- rated current hold-in test,

- overload test,

- adjustable instantaneous trip test (for maxi.num and minimum settings),and

- dielectric test Subsequent to the Bulletin tests, the licensee has performed additional testing of the breakers in accordance with their station procedure QEPM 200-4 for molded case' circuit breaker inspection and testing. This procedure adjusts'the instant 6neous-trip setting so that each (every) pole of the breaker will trip at 15 times the motor nameplate rating. The breaker is then tested at 9 times the motor nameplate rating to assure that no pole will spuriously trip during motor starting.

1 The four breakers at issue are the following:

Breaker No. 1; A 5 ampere normally closed breaker powered from a Class 1E 250V DC MCC. The breaker is in the control and motor circuit of valve M0-1-1301-62, RCIC Cooling Water to Lube Oil Cooler and Turbine Barometric Condenser. This valve is required to be open during RCIC System operation and is normally open. The valve is normally cycled twice a month during surveillance tests. The RCIC System is not a safety-related system at Quad Cities.

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9007190368 900717 PDR ADOCK 05000254 O PDC

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.,; 2-Breaker No. 2: A 25 ampere normally closed breaker powered from a Class 1E 250V DC MCC. The breaker is in the control and motor circuit of valve M0-1-2301-36, HPCI Upstream Suction from the Suppression Pool. The valve is normally closed but is required to open upon low level in the Contaminated Condensate Storage Tank or upon high level in the Suppression pool. Additionally, the valve receives isolation signals for closure under certain conditions. The valve is normally cycled once a month during a surveillance test. The HPCI System is a safety-related system at Quad Cities.

Breaker No. 3: A 5 ampere normally closed breaker powered from a Class 1E 480V AC MGC. The breaker is in the control and motor circuit of valve M0-1-1201-80, RWCU System Return to Reactor Header Isolation. The valve is open during opera-tion of the RWCU System. The valve does not perform a containment isolation or any other safety function, however, it closes under certain isolation signals.

Breaker No. 4: A 5 ampere normally closed breaker powered from a Class 1E 250V DC Mcc The breaker is in the control and motor circuit of valve M0-1-220-2 Main Steam Line Drain Outboard Isolation Valve. The valve is a safety-related prlmary containment isolation valve which is cycled once a quarter daring surveillance testing.- The valve is normally closed but must be opened to provide a flow path to drain the main steam lines during startup and shutdown of the unit. It must also be opened when the reactor is at pressure and the MSIV's are shut, to pro-vide a flow path to allow pressure equalization across the Main Steam Isolation Valves (MSIV's).

EVALUATION All four replacement breakers are normally closed and in the circuitry of motor operated valves. Each breaker's function is to remain closed during motor starting and running as required to open or close its associated valve, but to open for short circuits to protect the circuit and equilment against the short and to isolate the shorted circuit in time to prevent tie effects of the short from cascading to the upstream bus.

As discussed previously, all'four breakers have been tested against the criteria of NRC Bulletin 88-10. Each of these tests were successful exce)t in two instances.

Breaker No. 2 failed the adjustable instantaneous trip test at t1e minimum setting in that it failed to trip upon the application of a trip current of 125 percent of that specified for that setting. However, the application of the breaker at Quad Cities does not require the breaker to trip at a minimum value. Thus this failure would not affect the functioning of the breaker for the purpose for which it is to be used. The other test failure occurred when Breaker No. 4 failed the adjustable instantaneous trip test at the maximum trip setting in that the center pole tripped upon the application of a trip current of 80 percent of that specified for that setting. However, the center pole is not used for this application and would not affect the functioning of the breaker for the purpose for which it is to be used.

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'i l For the above breakers two types of failure are possible. Aspurious(uncalled

-for) opening of the breaker could occur, most likely while the motor is opening or closing a valve, but possibly even during the standby mode. Since all of the valves are normally closed or normally open and not cycled except during surveillance testing, the circuit breakers are not likely to fail due to repeated l challenge. Further, if a breaker should fail by spurious opening during surveil-lance testing, the failure would be immediately detected and appropriate action could be taken. ].

l The second type of failure that could occur is a failure to open for a fault I down-stream of the breaker. Such a failure could cascade to the upstream bus. l

'I However, this type of failure, and also the spurious opening type of failure, are bounded by a fault on the associated bus. Quad Cities is designed for a bus failure on each of the 250V DC or 480V AC buses associated with the breakers I in question, i Since the breakers have been thoroughly tested against the criteria of Attach-ment 1 of NRC Bulletin 88-10, we would not expect them to fail during the time.

they are to be used, particularly since they remain normally closed, except during surveillance testing, and are to be replaced by fully qualified breakers in the near future. Although Breaker Nos. 2 and 4 did not pass all of the tests specified in Attachment 1 of the Bulletin, they did pass those tests relevant to their particular function. Thus, we find the breakers to be acceptable for this particular use (but not for other uses)'for a limited period of time until they '

can be replaced by fully qualified breakers.

SUMMARY

AND CONCLUSION Four molded-case circuit breakers failed during surveillance testing during the >

1ast Quad Cities refueling outage. The only breakers available and suitable for replacing these breakers were not traceable to the orfginal manufacturer and therefore did not meet the requirements of NRC Bulletin 88-10 except through <

testing in accordance with Attachment A of the' Bulletin.  ;

The licensee tested the replacement breakers in accordance with the Bulletin and requested the NRC for permission to use the replacement breakers until fully-qualified breakers could be obtained and installed. The licensee now t has fully qualified breakers and plans to install them during the first reactor shutdown of sufficient duration.

The NRC granted preliminary approval to use the replacement breakers during teleconferences on November 20 and 22, 1989. Subsequently, the licensee sub- l

.mitted formal requests on November 20 and 29, 1989, to use the replacement '

breakers.

Although some of the replacement breakers which are to be used on a temporary basis did not meet all of the test requirements of Appendix A of the NRC Bulletin 88-10, they did meet those tests applicable to their particular application. We therefore, find them to be acceptable for temporary use for this application, but not for other applications.

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