ML20127N870
| ML20127N870 | |
| Person / Time | |
|---|---|
| Site: | Monticello, Prairie Island  |
| Issue date: | 08/09/1974 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Wachter L NORTHERN STATES POWER CO. |
| References | |
| IEB-74-09, IEB-74-9, NUDOCS 9212010440 | |
| Download: ML20127N870 (1) | |
Text
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i UNITE 3 STATES I.
ATOMIC ENERGY COMittS$10N DIRECTOR ATE OF REGULATOR Y OPER AYlONS
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Northera statas Fever Compsay Esaket No. 50-163 ATill Mr. Lee Washtar Dooket Me. 50-181 Vies Freefdent Docket No. 50-306 Power Fredmettom and System Operation 414 Miso 11st Hall Minnaapolis, Minnesota
$4401 Centleasa:
The enclosed DRO Bulletin No. 74-9, "Deficiamey in the General Electrie Hodal 4KV Magne-Blast Cirewit Breakers," is being seat to you relatias experience with some of these aircuit breakare at Vermont Tankee and Calvert Cliffa nuclear fmailities.
This information may have applis G ity at your facility.Aetion on your part is identified La sectima 3 of the miased Bulletin.
Sincerely.
l James C. Keppler Ragional Director l
Emelesurs:
DnD Bu11stin No. 74-9 bect ROJ11es tDff Central Files Local PDR PDR
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4 9212010440 740809 PDR ADOCK 05000263 G
.L August 9, 1974 DRO Bulletin No. 74-9
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DEFICIENCY IN CENERAL ELECTRIC MODEL 4KV MAGNE-BLAST BREAKERS We have recently received information from the licensee of Calvert Cliffs Units 1 and 2 relating to circuit breaker malfunctions in engineered These circuit breakers, General Electric Model 4KV safety systems.
safety Magne-Blast are used extensively at both PWR and BRR facilities.
The malfunctions, which could negate operation of engineered safety system components, were attributed to an oversized roller trip bar and improper clearances of related guide holes and linkages.
We have also received information from the licensee of Vermont Yankee station describing an installation deficiency of the auxiliary switch assembly installed in the General Electric Model 4KV Magne-Blast circuit breakers. Although the circuit breakers are similar in model to the units used at Clavert Cliffs, they are of a different type and are used at both PWR and BWR facilities.
Pertinent details relating to both problems are contained in Section A below, and the related action requested by this Bulletin is contained in Section B.
A.
Description of Circumstances Calvert Cliffs Unito 1 and.2 On several occasions in the past, there had been unexplained " trip open" operations of several 4KV circuit breakers. On each occasion, the anomaly c-surred immediately following an attempt to close the circuit breakers. Investigation into the problem disclosed that causes for failure were attributed to an oversized spring discharge roller bar located on the right side of the breaker cubicle and improper clearances in the roller bar guide hole and associated linkages. The purpose of the roller bar is to trip open the k
breaker unit in the event it is inserted into the breaker cubicle l
while in its closed position.
However, the installed roller bars
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were found to be approximately 1/4" longer than the design length, J
causing interference with the breaker auxiliary switch linkage.
Approximately 116 circuit breakers of the make and model described herein and equipped with the faulty roller bars and the above mentioned clearance problem are used in the two nuclear units at the facility.
Because we are requesting that you determine whether or not the subject breakers are used or are planned to be used at your facility the following details are provided for your information:
Manufacturer: General Electric Company Auxiliary Switch Assemblies in MC-4.76 Horizontal Drawout Metal Clad Switchgear
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Vermont Yankee The licensee reported that while investigating a' problem involving a station service water pump 4KV circuit breaker, an electrician noted that the breaker stationary auxiliary switch assembly rear mounting bolt had loosened and was disengaged from its mounting plate. The loose bolt is one of two bolts that assist in maintain-ing proper switch contact alignment. The loosening and disengage-ment of the tie bolt caused misalignment of_the switch auxiliary ~
contacts which could have rendered those contacts inoperable.
Inspection of similar switch assemblies installed in forty-seven 4KV circuit breakers at this facility found that all switch assemblies exhibited varying degrees of bolt loosening.
Because we are requesting _that you determihe whether or not the 4
subject devices are used or are planned to be used at your facility, the following details are provided for your information:
Manufacturer: General Electric Company _
Type: Hetal Clad, M26 Switchgear (This switchgear has the auxiliary switch assembly mounted to it and may be used with a large number of different circuit' breakers.)
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B.
Action Requested It is requested that you determine whether safety related (Class IE) circuit breakers of the described makes and models are in-stalled at your facilities and provide the RO Regional Office with-your findings within 20 days from receipt of this bulletin.
With regard to'the problem at Calvert Cliffs Units 1 and 2, if the
. subject breakers are installed, please include in your response a l
description and the results of your _ program' to determine if' you have. oversized roller trip bars installed and the scheduled com-i pletion date of your corrective actions. For facilities under construction, please inform us of your plans to assure that appropriate i-modification has been implemented in all. safety related circuit breakers of the type described that have been or will be inst'alled:
at'your facility.
With regard to the Vermont Yankee problem, it is requested that you ascertain the bolt tightness conditions of the switch assembly in-question and include in your response a description and the results of your inspection' program concerning these matters.
It is also requested that you inform us of your plans regarding the-long term verification of bolt tightness of the_ switch assemblies.
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