05000255/FIN-2011014-09
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Finding | |
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| Title | Potential Loss of Preferred AC Sources in Harsh Environment |
| Description | On September 25, 2011, a fault occurred on Panel D11-2, which resulted in reactor and turbine trip, and de-energiziation of Bus D-10. Breaker 72-37, which supplied DC power to Inverter D-06, was found tripped. According to the manufacturer, the inverters were capable of reverse-feeding DC short circuits for short durations and this could have caused Breaker 72-37 to trip. This was possible because the inverter had four 7700 microFarad parallel capacitors on the DC side of the inverter. During a DC short circuit, the capacitors would rapidly discharge and feed the fault. Breaker 72-37 had a rating of 100 Amps for the thermal setting and 700 Amps for the magnetic setting. According to the manufacturer an approximation for an inverter DC fault current contribution was about 1100 Amps per capacitor; therefore, this was approximately a total of 4400 Amps for Inverter D-06. This exceeded the magnetic rating of the breaker and explained why the breaker tripped during the fault condition. The PCP motor DC oil lift Pumps P-81A and P-81C were nonsafety-related loads, which received power from Bus D-10 via safety-related Breakers 72-13 and 72-14, respectively. The PCP motor DC oil lift Pumps P-81B and P-81D were also nonsafety-related loads that received power from D-20 via safety-related Breakers 72-23 and 72-24, respectively. The cabling for these loads was not environmentally qualified and was routed through containment, which could be susceptible to failure due to a harsh environment. The inspectors were concerned that if all four nonsafety-related cables for these pumps faulted due to a harsh environment during a design basis event, this could result in the loss of all preferred AC power busses due to the internal capacitors contributing to the fault as seen by each DC bus. However, without further analysis of the design and licensing basis, the inspectors could not determine if a postulated harsh environment affecting all four cables during a design basis event was a credible event. Therefore, the inspectors initial conclusion, based on the available information was that this event may not be credible; however, further analysis was required. In addition, all four PCP motor DC oil lift pump breakers were opened as one of the compensatory measures for the operability of the 125-Volt DC system. Therefore, this is not a current safety concern. Title 10 CFR 50.49, Environmental Qualification of Electrical Equipment Important to Safety for Nuclear Power Plants, Section b(2), requires nonsafety-related electric equipment to be environmentally qualified if the failure of the nonsafety-related electric equipment under postulated environmental conditions could prevent satisfactory accomplishment of safety functions specified in subparagraphs (b)(1)(i) (A) through (C) of paragraph (b)(1) of this section by the safety-related equipment. The inspectors were concerned that the cables associated with the PCP motor DC oil lift Pumps P-81A, P-81B, P-81C, and P-81D were not evaluated for the effect on the safety-related equipment specifically the safety-related inverters and their associated preferred AC sources. The licensee entered this issue into their CAP as CR-PLP-2011-6210. This issue is a URI pending the licensee evaluation, and the inspectors review of the licensees design and licensing basis, and evaluation to determine if a performance deficiency existed (URI 05000255/2011014-09; Potential Loss of Preferred AC Sources in Harsh Environment). |
| Site: | Palisades  |
|---|---|
| Report | IR 05000255/2011014 Section 4OA5 |
| Date counted | Dec 31, 2011 (2011Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 93812 |
| Inspectors (proximate) | M Holmberg C Zoia J Lennartz T Taylor J Gilliam A Scarbeary R Edwardsa Scarbearye Duncan E Sanchez Santiago J Cassidy J Laughlin M Holmberg M Phalen N Feliz Adomo T Taylora Dahbura Scarbeary J Giessner R Krseka Scarbearya Schwab B Boston C Zoia E Duncan J Cassidy J Lennartz R Latta R Morris A Garmoe |
| INPO aspect | |
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Finding - Palisades - IR 05000255/2011014 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Palisades) @ 2011Q4
Self-Identified List (Palisades)
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