05000282/FIN-2007003-01
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Finding | |
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Title | Failure of the 12 Safety Injection Pump Breaker |
Description | On April 3, 2007, during the performance of SP 1322, Safeguards Busses Weekly Inspection - Operating, Revision 20, operators identified that the closing springs were discharged on Breaker 16-7. Breaker 16-7 is the 4.16 kilovolt (KV) alternating current breaker for the 12 SI pump, a safety-related and risk-significant mitigating system component. Operators declared the 12 SI pump inoperable and entered TS Limiting Condition for Operation (LCO) 3.5.2, Condition A, at 7:29 p.m. Operators verified that breaker control power was available and the breaker was racked into bus 16 with auxiliary contacts properly engaged. Based on the actions taken by the operators, the problem was suspected to be internal to the breaker; therefore, the licensee replaced Breaker 16-7 with a spare breaker. Operators demonstrated operability of the 12 SI pump, and exited LCO 3.5.2, Condition A, at 4:01 a.m. on April 4, 2007. The licensee entered the deficient condition into the corrective action program with CAP 01085806. Electrical maintenance personnel performed failure analysis of Breaker 16-7 under WO 323973. During initial bench testing, Breaker 16-7 operated sporadically. Electrical maintenance personnel measured the resistance of the closing spring charging motor and observed that resistance varied from several ohms to seven mega-ohms. On closer inspection of the closing spring charging motor, electrical maintenance personnel observed that one of the motor brushes demonstrated excessive wear. Signs of arcing and charring were also observed between the brush and commutator. The inspectors reviewed the licensees historical operability evaluation CAP 01085806, Action 07, with respect to determining when the failure occurred. The licensee concluded that the closing springs failed to charge the last time the breaker was closed. The operating logs indicated the 12 SI pump breaker was last closed on March 15, 2007, when the 12 SI pump was run for a routine surveillance test. The inspectors reviewed the breaker operating sequence in the technical manual and compared the sequence described to the logic used by the licensee in the determination of the time of failure. The inspectors found that the licensees conclusion was supported by the technical manual. Based on the evaluation of historical operability, the 12 SI pump would not have been available if required from March 15 through April 4, 2007. The inspectors reviewed all operating log records associated with the 12 SI pump from March 15 to April 3, 2007, noting that SP 1322 had been performed by operators on two previous occasions (March 20 and March 27, 2007) prior to the discovery on April 3, 2007, of the discharged closing spring on Breaker 16-7. Step 11.2.10 of SP 1322 directed the performer of the procedure to verify that the closing springs were charged for all bus 16 breakers that were in service. The inspector reviewed CAP 01085806, Action 10, that reviewed operator performance. Based on interviews of the operators that performed SP 1322 on March 20 and March 27, 2007, both operators accurately described what was thought to be the proper method to verify the charged status of the closing springs. A more detailed review of the operator actions is being evaluated as part of the root cause evaluation which is not yet complete. The root cause evaluation team evaluated the possibility that the closing spring was partially charged following operation of the 12 SI pump March 15, 2007. The potential exist that the operators performing the 12 SI pump breaker checks on March 20 and on March 27, 2007, observed the yellow coloring on the tags on the closing spring guides when viewed through the shutter door opening in the breaker door. Per SP 1322, the ability to see yellow on the tags on the closing spring guides would indicate the spring was in the charged state. The inspectors observed an operator check the state of the charge of a closing spring on a similar breaker and compared the observed action to the direction provided in Step 11.2.10 of SP 1322. The inspectors noted that operators could possibly conclude that the closing spring was charged when it was actually still in the discharged state. This observation was discussed with the shift manager and additional investigation was initiated by the licensee for this aspect of the issue. The licensee concluded that knowledge and methodology differences existed among operators performing checks of 4.16 KV closing spring breakers. The licensee entered this condition into their corrective action program with CAP 01098025 on June 20, 2007. This issue is considered an Unresolved Item (URI)05000282/2007003-01 pending completion of the licensees root cause evaluation. The inspectors subsequent review of the evaluation will determine whether the 12 SI pump motor circuit breaker would have closed with the partially charged closing spring, and the adequacy of the procedure for performing the 4.16 KV closing spring surveillance. |
Site: | Prairie Island ![]() |
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Report | IR 05000282/2007003 Section 1R22 |
Date counted | Jun 30, 2007 (2007Q2) |
Type: | URI: |
cornerstone | Mitigating Systems |
Identified by: | NRC identified |
Inspection Procedure: | IP 71111.22 |
Inspectors (proximate) | C Zoia D Mcneil S Ray M Phalen S Orth C Thomas L Haeg D Karjala R Walton P Zurawski R Skokowski P Laflammer Jicklingn Valos M Phalen J Adams M Gryglak D Karjala S Bakhsh |
INPO aspect | |
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Finding - Prairie Island - IR 05000282/2007003 | |||||||||||||||||||||
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Finding List (Prairie Island) @ 2007Q2
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