05000259/FIN-2009004-01
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Finding | |
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| Title | Unit 3 Reactor Core Isolation Cooling Pump Flow Oscillations |
| Description | The inspectors identified an issue associated with the operability evaluation of the Unit 3 RCIC System flow oscillations (PER 200183). This issue is being characterized as an unresolved item (URI). Following the Unit 3 Reactor scram on August 24, 2009, the RCIC system auto-initiated as designed and injected into the vessel restoring reactor water level. The RCIC pump ran for approximately 2 12 minutes. Subsequent review of RCIC system operating parameters by the system engineer revealed an unexpected level of instability in system flow and turbine control system response. Unit 3 RCIC flow was determined to be oscillating from approximately 300 gallons per minute (gpm) to 900 gpm on a five second period. The cause of these oscillations was not identified. The licensee determined that RCIC was operable but degraded based on an average flow greater than the minimum required 600 gpm, adequate margins to the over-speed and high turbine exhaust pressure trips, and because the oscillations appeared stable with no apparent divergence in amplitude or frequency. However, the licensees functional evaluation was based on turbine performance for a very short period of time and concluded that this performance would not change during the required mission time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or over the range of reactor pressures RCIC would be required to operate under. Unit 3 was restarted following the scram on August 27, 2009, but was removed from service on September 12, 2009, to repair a Main Generator hydrogen leak. During this maintenance outage the RCIC turbine electronic governor regulator (EGR) was replaced and the flow control loop was calibrated. Subsequent post-maintenance testing (PMT) included operating RCIC in the injection mode, which was completed with no oscillations noted. Based on an acceptable PMT, Unit 3 RCIC was declared fully operable and returned to service after restart of Unit 3 on September 18, 2009. 10 Enclosure The EGR that was replaced following the August 27 scram had been installed since March 2006. This EGR had experienced similar flow oscillations while in the reactor vessel injection mode following a Unit 3 scram on February 9, 2007, (PER 119628 and PER 168144). The licensees corrective actions to address the Unit 3 RCIC flow oscillations following the 2007 scram, included manual stroking of the RCIC governor valve, control loop calibration, repair of a broken terminal screw and adjustment of the compensating needle valve on the EGR. However, these corrective actions did not include replacing the EGR, and the PMT only operated RCIC in the Condensate Storage Tank (CST) recirculation mode (not in the reactor pressure vessel injection mode). At that time, the licensee concluded their corrective actions were sufficient to resolve the flow oscillations, and they believed RCIC operability was adequately demonstrated by the PMT (i.e., CST recirculation). Following the Unit 3 scram on August 27, 2009, it was revealed that the previous corrective actions and testing did not resolve the excessive flow oscillations. The inspectors questioned the basis of the licensees past operability determination which presumed that the flow oscillations would remain constant over a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> mission time, and at different pressure conditions in the reactor vessel, without knowing the definitive cause of the oscillations. Further review of the licensees methodology used for determining whether the 600 gpm minimum flowrate TS requirement 3.5.3.3 was met, during the high frequency flow oscillations between 300 gpm and 900 gpm, will be conducted. The licensee has developed a corrective action contained in PER 200183 to have the EGR vendor conduct additional testing and/or inspection of the replaced EGR to determine the cause of the oscillations. Following the EGR vendor evaluation and the licensees assessment of past operability, the inspectors will review the results. Additional information from the licensee regarding the root cause of the flow oscillations, and past operability determinations, will be needed to resolve the inspectors concerns. Consequently, pending additional information from the licensee and further review by the NRC, this issue will be identified as URI 05000296/2009004-01, Unit 3 Reactor Core Isolation Cooling Pump Flow Oscillations |
| Site: | Browns Ferry  |
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| Report | IR 05000259/2009004 Section 1R15 |
| Date counted | Sep 30, 2009 (2009Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.15 |
| Inspectors (proximate) | C Stancil T Ross E Guthrie C Young K Korth |
| INPO aspect | |
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Finding - Browns Ferry - IR 05000259/2009004 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Browns Ferry) @ 2009Q3
Self-Identified List (Browns Ferry)
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