View source for PNO-V-85-033A, Channel C Reactor Trip Breaker Failed.Caused by Incorrect Measured Armature to Rivet Clearance & Trip Paddle Where Contacting Armature Plate Squared Off.Other Reactor Trip Breakers Reexamined

{{Adams
| number = ML20126F134
| issue date = 06/10/1985
| title = PNO-V-85-033A:Channel C Reactor Trip Breaker Failed.Caused by Incorrect Measured Armature to Rivet Clearance & Trip Paddle Where Contacting Armature Plate Squared Off.Other Reactor Trip Breakers Reexamined
| author name = Miller L
| author affiliation = NRC OFFICE OF INSPECTION &amp; ENFORCEMENT (IE REGION V)
| addressee name = 
| addressee affiliation = 
| docket = 05000312
| license number = 
| contact person = 
| document report number = PNO-V-85-033A, PNO-V-85-33A, NUDOCS 8506170362
| document type = PRELIMINARY NOTIFICATION OF EVENT OR OCCURRENCE (PNO,, TEXT-INSPECTION &amp; AUDIT &amp; I&amp;E CIRCULARS
| page count = 1
}}
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PRELIMINARY NOTIFICATION 0F EVENT OR UNUSUAL OCCURRENCE-PNO-V-85-33A Date: 6/10/85 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. ,The information presented is as initially received without verification
          ,cr evaluation and'is basically all'that is known by Region V staff on this date.
      .      FACILITY:                                                           Emergency Classification-Sacramento Municipal Utility District                    Notification of Unusual Event Rancho Seco Nu_ clear Power Plant                        Alert Sacramento, CA                                           Site Area Emergency Docket No. 50-312                                        General Emergency XX_Not Applicable

==SUBJECT:==
REACTOR TRIP BREAKER FAILS TO OPEN DURING SURVEILLANCE TESTING (UPDATE)
AsLofi 8:00 AM,' June-10, 1985,. the licensee and technical representatives of General.
:Elsctric;(Atlanta) and Babcock and Wilcox (Lynchburg) have identified two possible crures"for the failed Channel "C" reactor trip' breaker (RTB)._ The failed breaker,
_ BTW Serial No. 224A3515-506GG-1, GE Type AK'2-25, had a measured armature to rivet
         .clesrance of 0.059_ inches (factory set tolerance is supposed to be 0.001 to.0.010 inches). In addition, the shape of the. trip paddle where it contacted the armature plate was squared off rather'than rounded. The licensee intends to preserve the bruker in the as found condition to allow other interested parties' to examine it prier-to making any adjustments.
l All other reactor trip break'ers were reexamined. No'significant discrepancies were discovered with these breakers. However,,the measurement of armature to rivet clstrance was found to be sensitive to the armature position, contrary to GE Service
          -Bulletin 25-014. The GE. technical representative noted.that, at the factory, this elserance was' set with the armature in the coil energized' position. Minor variances in;undervoltage dropout. voltages,'one trip bar torque setting, and a. missing lockwire,
          . ware noted also, but the technical representative and_the licensee concluded these
          =w;ra small enough to be insignificant.in'affecting breaker operation.
Tha licensee has declared six reactor trip breakers which have been successfully
           ;tssted.to be operable, and intends to startup today. Region V will review the ilicsnsee's actions to conclusively-determine the.cause of the failed Channel "C" RTB.
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This information is current-as of 10:00 AM (PDT) June 10, 1985.
CONTACT:    L. Miller
                        -FTS 463-3869-1 DISTRIBUTION IH ;. S t .-      O[       MNBB*        hillip E/    Willste     Air Right        Mail:
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* 5~/ NSAC                                               i ACRS                                  Licensee: 8'r1
         ~ CA --                                   (Reactor Licensees           REGION V: FORM 211                 :
         .PDR-                                     Resident Inspector [) */O         (Revised 3/14/83) 8506170362 850610 PDR   18sE PNO-V-85-033A PDR                       ggg/4                   gJ-}}

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