United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 74-09


.

                                                            IEB 74-09

                                 UNITED STATES
                           ATOMIC ENERGY COMMISSION
                     DIRECTORATE OF REGULATORY OPERATIONS
                                   REGION I
                                631 PARK AVENUE
                      KING OF PRUSSIA, PENNSYLVANIA 19406

                                       August 6, 1974


Consolidated Edison Company of New York, Inc.              Docket No. 50-286
Attention:  Mr. W. J. Cahill, Jr.
            Vice President
4 Irving Place
New York, New York  10003

Gentlemen:

The enclosed DRO Bulletin No. 74-9, "Deficiency in the General Electric
Model 4KV Magne-Blast Circuit Breakers," is being sent to you relating
experience with some of these circuit breakers at Vermont Yankee and Calvert
Cliffs nuclear facilities.

This information may have applicability to your facilities.  Action on your
part is identified in Section B of the enclosed Bulletin.

                                       Sincerely,



                                       James P. O'Reilly
                                       Director

Enclosure:
DRO Bulletin No. 74-9

cc:  A. D. Kohler, Jr., Resident Construction Manager
     A. E. Upton, Esquire

.

                                            Directorate of Regulatory
                                            Operations Bulletin 74-9
                                            August 6, 1974

DEFICIENCY IN GENERAL ELECTRIC MODEL 4KV MAGNE-BLAST BREAKERS

We have recently received information form the licensee of Calvert Cliffs
Units 1 and 2 relating to circuit breaker malfunctions in engineered safety
systems.  These circuit breakers, General Electric Model 4KV safety
Magne-Blast are used extensively at both PWR and BWR facilities.  The
malfunctions, which could negate operation of engineered safety system
components, were attributed to an oversized roller trip bar and improper
clearences of related guide holes and linkages.

We have also received information from the licensee of Vermont Yankee Station
describing an installation deficiency of the auxilliary switch assembly
installed in the General Electric Model 4 KV Magne-Blast circuit breakers. 
Although the circuit breakers are similiar in model to the units used at
Calvert 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 Units 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
occurred 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 clearences in the roller bar guide
hole and associated linkages.  The purpose of the roller bar is to trip open
the breaker unit in the event it is inserted into the breaker cubicule while
in its closed position.  However, the installed roller bars were found to be
approximately 1/4" longer than the design length, causing interference with
the breaker auxiliary switch linkage.

Approximately 116 circuit breakers of the make and model describe herein and
equipped with the faulty roller bars and the above mentioned clearence problem
are used in the two nuclear units at this 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:

.

RO Bulletin No. 74-9                - 2 -


            Manufacturer:  General Electric Co.
            Auxiliary Switch Assemblies in MC-4.76 Horizontal Drawout
            Metal Clad Switchgear with AMH-4.76-250 Breaker

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 maintaining proper switch contact alignment.  The loosening and
disengagement of the tie bolt caused misalignment of the switch assemblies
installed in forty-seven 4KV circuit breakers at this faccility found that all
switch assemblies exhibited varying degrees of bolt loosening.

Because we are requesting that you determine whether or not the subject
devices are used or are planned to be used at your facility, the following
details are provided for your information:

            Manufacturer:   General Electric Co.
            Type: Metal Clad, M26 Swithgear (This switchgear has the
                  auxiliary switch assembly mounted to it and may be
                  used with a large number of different circuit breakers.)

B.  Action Requested

It is requested that you determine whether safety related (Class IE) circuit
breakers of the described makes and models are installed 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 description and the
results of your program to determine if you have oversized roller trip bars
installed and the scheduled completion date of your corrective actions.  For
facilities under construction, please inform us of your plans to assure that
appropriate modification has been implemented in all safety related circuit
breakers of the type described that have been or will be installed 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.

.

RO Bulletin No. 74-9                - 3 -


Should you have any question concerning this matter, we will be pleased to
discuss them with you.

Page Last Reviewed/Updated Tuesday, July 23, 2013