United States Nuclear Regulatory Commission - Protecting People and the Environment


LICENSEE: COMMONWEALTH EDISON                

SITE: COMMONWEALTH EDISON                   EN NUMBER:33917

DOCKET:                                  EVENT DATE: 03-16-98

RX TYPE:                                 EVENT TIME: 00:00

VENDORS:                                NOTIFY DATE: 03-18-98

EMERGENCY CLASS: N/A  REGION: 3 STATE: IL      TIME: 16:37

OPS OFFICER: LEIGH TROCINE            

10 CFR SECTION: CCCC  21.21               UNSPECIFIED PARAGRAPH



10CFR PART 21 NOTIFICATION REGARDING SPRING RETURN BINDING IN    

GENERAL ELECTRIC (GE) TYPE SBM CONTROL SWITCHES AT DRESDEN,      

LASALLE, AND QUAD CITIES.                                        

                                                                 

THIS NOTIFICATION REFERENCED A GE NUCLEAR ENERGY TRANSFER OF     

INFORMATION DATED JANUARY 23, 1998, AND IT INVOLVES GE TYPE SBM  

CONTROL SWITCHES WITH THE SPRING RETURN FUNCTION MANUFACTURED    

SINCE MARCH 1996.  THESE SWITCHES ARE SUSCEPTIBLE TO BINDING     

WHICH MAY PREVENT SPRING RETURN TO RESET (RETURN TO NORMAL       

POSITION).  THE CAUSE OF THE BINDING WAS ATTRIBUTED TO FAILURE TO

ACCOUNT FOR 'POST-MOLD CURE' SHRINKAGE IN THE DESIGN TOLERANCE OF

THE CLEARANCE BETWEEN THE PHENOLIC REAR BEARING SUPPORT HOLE AND 

THE BEARING. THIS DESIGN ERROR DID NOT BECOME APPARENT UNTIL THE 

MOLDS EXPERIENCED WEAR TO THE EXTENT THAT RESULTING PARTS WERE AT

THE EXTREMES OF DIMENSIONAL TOLERANCES.  THE POST-MOLD CURE IS   

NORMAL FOR PHENOLIC MATERIAL AND HAS BEEN SHOWN TO TAKE PLACE    

OVER A PERIOD OF UP TO TWO YEARS AFTER MOLDING IS COMPLETED.     

CONSEQUENTLY, SWITCHES WHICH ARE CONSTRUCTED FROM COMPONENTS

THAT

ARE WITHIN SPECIFICATION AND FUNCTION FULLY DURING ACCEPTANCE    

TESTING MAY EXHIBIT SLUGGISH RETURN OR BINDING UP TO TWO YEARS   

AFTER ASSEMBLY. THIS ROOT CAUSE IS SUPPORTED THROUGH GE          

EXAMINATION OF FAILED SWITCHES WHICH, IN EACH INSTANCE, HAS FOUND

THE BEARING SUPPORT HOLE TO BE UNDERSIZED (LESS THAN MINIMUM     

INSIDE DIAMETER) AND THE BEARING AT OR NEAR ITS MAXIMUM ALLOWABLE

DIAMETER.  GE TESTING HAS ALSO CONFIRMED THAT SWITCHES WITH      

BEARINGS THAT ARE AT THEIR NOMINAL DIAMETER WILL FUNCTION        

PROPERLY EVEN WHEN THE SUPPORT HOLE IS UNDERSIZED.  CONSEQUENTLY,

THE FAILURE IS NOT SEEN IN EVERY SWITCH.                         

                                                                 

COMMONWEALTH EDISON HAS DETERMINED THAT THE SUSPECT SBM SWITCHES 

ARE NOT INSTALLED AT ITS BRAIDWOOD, BYRON, OR ZION NUCLEAR       

GENERATING STATIONS. HOWEVER, COMMONWEALTH EDISON NUCLEAR        

GENERATING STATIONS WHICH HAVE THE SUSPECT SAFETY-RELATED SPRING 

RETURN SWITCHES INCLUDE DRESDEN, LASALLE, AND QUAD CITIES WITH 2,

246, AND 3 SWITCHES INSTALLED, RESPECTIVELY.  LASALLE IS         

CURRENTLY EXPERIENCING BINDING IN 21 OF THESE SWITCHES.          

                                                                 

THE FOLLOWING FACILITIES WERE ALSO REPORTED TO BE AFFECTED:      

PILGRIM; RIVER BEND; OYSTER CREEK; COOPER; FITZPATRICK; MILLSTONE

UNIT 1; HATCH UNITS 1 AND 2; BROWNS FERRY UNITS 1, 2, AND 3;     

VERMONT YANKEE; PALISADES; ARKANSAS NUCLEAR ONE UNITS 1 AND 2;   

TURKEY POINT UNITS 3 AND 4; CRYSTAL RIVER UNIT 3; MAIN YANKEE;   

INDIAN POINT 3; SEABROOK; FORT CALHOUN; SALEM UNITS 1 AND 2; AND 

VOGTLE UNITS 1 AND 2.                                            





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