05000285/FIN-2011014-02
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Finding | |
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| Title | Failure To Perform Adequate 10 Cfr 50.59 Review |
| Description | The team identified an unresolved item related to the licensees implementation of the requirements in 10 CFR 50.59 for modification EC 33464, Replace AK-50 480 V Main and Bus-Tie Breakers With Molded Case Type or Equivalent, Revision 0, and the adequacy of the design review and screening performed to support the modification. In November 2009, the licensee implemented a modification to replace 12 General Electric AK-50 low voltage power circuit breakers with Nuclear Logistics Incorporated/Square-D Masterpact circuit breaker/cradle assemblies and digital trip devices. This modification was developed to address obsolescence issues and maintenance problems with the older AK-50 circuit breakers. Fort Calhoun Station used General Electric AKD-5 Powermaster Low Voltage Drawout Switchgear, with a welded aluminum bus bar structure that transitioned to copper bus stabs in each breaker cell. The original AK-50 circuit breakers connected directly to the silver-plated areas on the line and load stabs. The new Nuclear Logistics Incorporated /Square-D circuit breaker design was an integrated unit consisting of a circuit breaker and cradle assembly. The cradle assembly converted the internal vertical breaker connectors to top and bottom spring-loaded horizontal finger assemblies which connected to the switchgear bus stabs. The team reviewed the licensees implementation of the requirements in 10 CFR 50.59, Changes, Tests and Experiments, for the modification. The team noted that the screening process did not recognize the potential for adverse effects on the design basis function of the 480 Vac electrical distribution system because of the introduction of a cradle assembly that had different connections to the switchgear bus bars. The original breakers did not require the cradle adapter and had connector assemblies which mounted to the silver-plated portion of the bus bars. The new assembly introduced the cradle as an adapter between the breaker and switchgear, and introduced additional resistances in the circuits. The licensees screening documents stated that the electrical connections on the cradle matched the existing switchgear General Electric breakers; however, the licensees root cause analysis showed that the cradle finger assemblies were not the same size as the original breaker connections. The team also noted that the licensees screening process did not recognize the potential for high resistance connections to exist, and did not analyze additional failure mechanisms that may have been created by the addition of the cradle assemblies. Condition Report CR 2011-6319 was written, after the fire, for the discovery of the improper engagement of cradle fingers to silver plating on the stabs. Further inspection is required to determine if the licensees implementation of the requirements of 10 CFR 50.59 were appropriate. |
| Site: | Fort Calhoun  |
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| Report | IR 05000285/2011014 Section 4OA5 |
| Date counted | Mar 31, 2012 (2012Q1) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 93812 |
| Inspectors (proximate) | D Loveless G Miller J Josey S Achen S Gravesa Klett C Smith M Davis J Josey C Bickett G Warnick M Hay J Brand J Groom M Keefe R Latta W Schaup J Watkins B Hagar A Allen J Wingebach K Martin L Wilkins S Morrow R Deese F Ramire |
| INPO aspect | |
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Finding - Fort Calhoun - IR 05000285/2011014 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Fort Calhoun) @ 2012Q1
Self-Identified List (Fort Calhoun)
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