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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