ML20095G560
| ML20095G560 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 07/02/1984 |
| From: | Williams J FLORIDA POWER & LIGHT CO. |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| IEB-83-08, IEB-83-8, NUDOCS 8408280106 | |
| Download: ML20095G560 (6) | |
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FLORIDA POWER & LIGHT COMPANY L-84-166 July 2, 1984 Mr. Janes P. O'Reilly Regional Administrator, Region II U. S. Nuclear Regulatory Commission 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323
Dear Mr. O'Reilly:
Re: St. Lucie Unit 2 Docket No. 50-389 IE Bulletin 83-08 Florida Power & LigSt has completed the review of IE Bulletin 83-08 (Electrical Circuit Breakers With an Undervoltage Trip Feature in Use in Safety Related Applications Other than the Reactor Trip System). Our initial response for St. Lucie Unit 2 was provided in our letter L-84-83, dated March 29, 1984.
We have now completed a design review of the safety related breakers which utilize an undervoltage trip attachment, and have determined that the design margin available to open the breakers is sufficient to justify our current maintenance and surveillance program.
Our response to Item 2 of the Bulletin is attached. This completes our effort on this bulletin.
Should you or your staff have any questions on this information, please contact us.
Very truly yours,
/
J. W. W i ans, Jr.
Group Vice President Nuclear Energy JWW/PLP/js Attachment cc: J. P. O'Reilly, Region II Harold F. Reis, Esquire PNS-LI-84-223 0
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ATTACHMENT Re: St. Lucie Unit 2 Docket No. 50-389 IE Bulletin 83-08 FPL response to Question 2 of IE Bulletin 83-08 (Electrical Circuit Breakers With an Undervoltage Trip Feature in Use in Safety Related Applications Other Than the Reactor Trip System) for St. Lucie Unit 2.
Question 2a Review the design of the UVTA and the connecting linkage.
Using input from the breaker manufacturer, determine the design margin available to open the
- breaker. Evaluate whether or not this design margin is adequate in view of safety applications, considering possible problems of alignment, lubrication, adjustment of spring tension, etc., discussed in the " Description of Ci rcumst ances."
Response 2a EVALUATION OF UNDERVOLTAGE TRIP ATTACHMENTS INTRODUCTION IE Bulletin 83-08 requires holders of construction permits and licenses to respond to questions on the Undervoltage Trip Attachments (UVTA) circuit breakers other than Westinghouse and General Electric used in safety related applications. Paragraph 2a on page 3 of the bulletin requires a determination of the design margin available to open the breaker and whether or not this design margin is adequate in view of safety applications, considering possible problems of alignment, lubrication, adjustment of spring tension, etc. The discussions which follow are based on vendor input and field testing.
APPLICATION The UVTAs are used for isolating non-safety related loads from the safety buses on loss of power. The following is a list of circuit breakers, other than Reactor Trip Breakers, having UVTAs in safety-related applications. All of the circuit breakers listed are Brown-Boveri Electric Type K600.
Switchgear Compartment Lo ad l
2A2 28 Spare 4A Spare 4B 2 HVE-10A 4C CEA MG Set 2A 40 Spare 2B2 4A Spare 4B 2HVE-10B 4C CEA MG Set 2B l
4D Spare 6A RCB Crane #2 6B Spare 1
2A5 3A Spare 2B5 3A Spare
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p On all loads except the RCB Crane #2, dual trip signals are used, the UVTA and the shunt trip.
UVTA & BREAKER TRIP OPERATION The undervoltage rely on the K2000 and under is installed on the right side of the breaker (f acing the breaker). Dropout has a range of adjustment from 30 to 60% of rated voltage. A bracket with adjusting screw is attached directly to the plunger of the undervoltage device.
Upon dropout, a spring forces this assembly down against the breaker tripper bar. Per the manuf acturer, the tripper bar offers anple surf ace for the screw to act on to allow for some misalignment. The adjusting screw on the undervoltage plunger can be adjusted to act on a secondary 1atch directly beneath the tripper bar. The shunt trip device acts on this latch. Therefore, in the K2000 and under circuit breaker, there is a certain anount of redundancy in design because the undervoltage device can be made to also act on the latch on which the shunt trip operates.
Brown Boveri has addressed the following points to be considered in the UVTA evaluation:
1 1.
No lubrication is required or recommended for the UVTA.
2.
Gravity assists in the operation of the rely although it is not dependent on it for operation.
3.
The hardware used on the undervoltage devices is such that vibration due to breaker operation would not put it out of adjustment. Pins with crimped C-shaped retainers and bolts with lock washers or locking nuts ensure the integrity of the device.
4.
The undervoltage devices are located in sheltered locations in the breakers which expose then to les,s dust accumulation. The orientation of the magnet is such that accumulated dust would not build up between the magnet and annature.
Brown Boveri has infonned us that this UVTA design has been repeated on the market for nearly twenty years with no significant problens being reported.
. DESIGN MARGIN FPL electrical maintenance personnel at the plant performed tests on each of the breakers of concern to determine the actual force required to trip the breaker and the force available by the UVTA.
Results of these tests are given below and the margin calculated.
Breaker Trip Undervolt age Margin j
gSw r Com )t.
Force (lbs)
Force (lbs) 2BZ 63 1.25 5
400 4A 1.0 5
500 4D 1.0 5
500 2A2 4A 1.25 5.25 420 4D 1.0 5
500 2B 0.75 5
667 2A5 3A 0.75 5
667 2B5 3A 0.75 5
667 According to the circuit breaker instruction manual, with the circuit breaker in the " CLOSED" position, the push required to trip the circuit breaker must be between 16 an 29 ounces.
Brown Boveri Corporation has infonned us that they normally do not assign quantities for the UVTA output nor the trip bar force requirement.
However, given a typical 5 pound force delivered by the undervoltage device and the 29 ounce trip force as a worst case requirement, the calculated design margin is 275%.
CONCLUSION Based on the results of the field tests and the input provided by the vender with regard to operation, lubrication and design of the UVTA.
FPL concurs with the manufacturer in that sufficient design margin is available to open the breaker.
Question 2b Describe the current breaker surveillance progran, including details of test frequency, methodology, and response time measurement of UVTA device.
Response 2b St. Lucie's current breaker surveillance progran requires the breakers mentioned in the response to Question 2a to be maintained in accordance with the plant maintenance procedure every five years. This procedure requires inspection for cleanliness, broken or loose parts, proper lubrication, tightened bolts, wiring connections, alignment and contact f aces. The operation checks require the breaker to open and close manually and electrically. The electrical tests check overcurrent devices for proper operation to manuf acturer's specifications.
, Question 2c Review operating experience with the circuit breakers in your plant (s) identified in Item 1.
Provide a list of all malfunctions (both f ailure to trip and f ailure to close on demand) associated with the UVTA, including the connecting linkages and latching mechanisms. The list should include the date of each malfunction, and the operating time prior to f ailure or date of installation, and the date(s) of major maintenance.
In general, when the circuit breaker UVTA is actuated on undervoltage and the breaker contacts do not open within the design time response value, then NRC considers the breaker to have f ailed.
Response 2c We are aware of no f ailures associated with these breakers at St. Lucie Unit 2.
Question 2d Describe any preventive or corrective measures you have taken, or intend to take, based on the results of Items 2a, 2b, and 2c. Include any revisions to the surveillance test program and methodology.
Specifically, address the inherent reliability of the UV trip feature in view of its apparent heavy dependence en intensive maintenance and surveillance and whether a basic design change is warranted to correct the problem, e.g., using a voltage sensitive relay to sense loss of voltage and er.ergize the shunt trip coil from an independent dc power source.
Response 2d Because of the results of the design margin evaluation and the absence of heavy dependence on intensive r,aintenance, we have concluded that our current program of breaker maintenance is sufficient and we consider that no additional measures are warranted.
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STATE OF FLORIDA
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COUNTY OF DADE
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C. 0. Woody, being first duly sworn, deposes and says:
That he is Vice President Nuclear Operations of Florida Power & Light Company, the licensee herein; That he has executed the foregoing document; that the statements made in this document are true and correct to the best of his knowledge, information, and belief, and that he is authorized to execute the document on behalf of said Licensee.
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[Aud C.O. Woody [
Subscribed and sworn to before me this h day of ( //////-
, 1984.
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4/l!ll l NOTARY PUBLIC, irr//
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/and for the County of Dade, State of Florida.
My commission expires:
NOTARY PUBUC STATE OF FLORIDA AT LAltOE MY COMMI5510ti EAPIRES DEC 41984 SONDtD THAU CD4ERAL lt6. Ut40ERWRITERS o
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