Part 21 Report - 1998-260
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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