05000266/LER-2007-005
| Docket Numberrev | |
| Event date: | 06-15-2007 |
|---|---|
| Report date: | 08-14-2007 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| 2662007005R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Point Beach Nuclear Plant 05000266 YEAR Event Description and Analysis On June 14, 2007, at 1819 hours0.0211 days <br />0.505 hours <br />0.00301 weeks <br />6.921295e-4 months <br /> a Unit 1 shutdown from 100% power was commenced in recognition of the failure to meet TSAC 3.7.5.B.1, the 72-hour completion time limit for 1P-29 TDAFW pump inoperability. The shutdown, conducted according to OP 3A, Power Operation to Hot Standby, was uneventful with all equipment and systems operating as expected. Due to the power reduction taking place at a rate greater than 15% per hour, iodine isotope sampling in accordance with TS Surveillance Requirement (SR) 3.4.16.2 was performed with acceptable results. Unit 1 entered MODE 3 on June 15, 2007, at 0407 hours0.00471 days <br />0.113 hours <br />6.729497e-4 weeks <br />1.548635e-4 months <br />, and MODE 4 at 1712 hours0.0198 days <br />0.476 hours <br />0.00283 weeks <br />6.51416e-4 months <br />. Both mode conditions were achieved within the Completion Time limits required by TS 3.7.5.
TSAC 3.7.5.B.1 had been initially entered on June 12, 2007, at 0131 hours0.00152 days <br />0.0364 hours <br />2.166005e-4 weeks <br />4.98455e-5 months <br /> when 1P-29 TDAFW pump was declared inoperable to perform a IT-08A test. During the test a high temperature on the outboard turbine bearing was identified. The TDAFW pump was secured at 0347 hours0.00402 days <br />0.0964 hours <br />5.737434e-4 weeks <br />1.320335e-4 months <br /> and remained inoperable. Repair efforts were not completed within the TS allowed Completion Time and the TS-required shutdown of the Unit 1 reactor was performed.
Cause
The cause of the event was the failure to complete repairs and return the TDAFW pump to operable status (e.g., satisfy the LCO) within the allotted time. The 10-year overhaul, done in April of 2007, during the U1R30 refueling outage, was conducted using an inadequate maintenance overhaul procedure. Inadequate PMT following the overhaul prevented the identification of equipment performance problems. Thus, the cause of the TS-required shutdown was personnel error, during the development of the overhaul procedure, and again during the specification of testing requirements following the overhaul.
Corrective Action Changes to the maintenance procedure for equipment overhaul, and changes to the process and procedures for specifying PMT, are being tracked using the plant's Corrective Action Program via CAP 01090456.
Safety Significance
The event, a unit shutdown required by TS, was of low safety significance. All TS-required conditions were met, and all systems and equipment performed as expected.
The nuclear safety significance, beyond the required TS shutdown was also considered, given the degraded condition of 1P-29 TDAFW pump as a result of improperly conducted maintenance and testing in April 2007.
The preliminary nuclear safety significance was determined to be moderate using probabilistic risk assessment tools. A detailed quantitative safety determination evaluation is in progress. Evaluation of internal events has determined the safety significance is low. The pump would have been able to batch feed water to the steam generators based on thermal/hydraulic analyses and performance of a simulator scenario.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Point Beach Nuclear Plant 05000266 YEAR Component and System Description The auxiliary feedwater (AFW) system automatically supplies feedwater to the steam generators to remove decay heat from the reactor coolant system (RCS) upon the loss of normal feedwater supply. The AFW pumps provide cooling water to the steam generator secondary side via connections to the main feedwater (MFW) piping inside containment. The steam generators function as a heat sink for core decay heat.
The AFW system consists of three independent pump systems; two motor-driven AFW pumps which are shared between the two units, and one dedicated steam turbine-driven pump per unit. Each motor-driven pump is capable of providing 100% of the design AFW flow rate, while the turbine-driven pump is capable of providing 200% of the design flow rate. Each pump is provided with a recirculation line to maintain pump discharge flow above the minimum required flow rate for pump cooling. Recirculation line orifices are sized to not be susceptible to clogging by service water debris. The debris size is limited by the size of the service water strainers. Each AFW pump system can be manually aligned to take suction from the service water system. The normal source of water for the AFW pumps is the condensate storage tank (CST) and the safety-related supply is the service water (SW) system. Motor-operated valves are provided to allow the suction supply for the AFW pumps to be manually transferred to the SW system.
Each motor-driven AFW pump is powered from an independent safeguards power supply and feeds one steam generator in each unit. AFW pump P-38A supplies AFW flow to the Unit 1 and Unit 2 'A' steam generators, while AFW pump P-38B supplies the Unit 1 and Unit 2 'B' steam generators. Each motor-driven AFW pump's discharge header contains two normally closed automatic motor-operated valves. Upon receipt of an AFW actuation signal, the discharge valve associated with the affected unit receives an automatic open signal and the discharge valve associated with the unaffected unit receives an automatic close signal. This feature will ensure that 100% of the motor-driven AFW pump flow will be delivered to the affected unit, thereby, assuring that the accident analysis flow rates are met. Each motor-driven AFW pump is also equipped with a backpressure control valve, which is designed to preclude the motor-driven AFW pump from tripping on an overcurrent condition at low steam generator pressures.
Each unit's turbine-driven AFW pump receives steam from both steam generator main steam lines upstream of the main steam isolation valves. Each of the two steam feed lines can supply 100% of the required steam flow to the turbine-driven AFW pump. Turbine-driven AFW pump 1P-29 is powered by a ZS frame Terry turbine equipped with ring oilers only and has a unique bearing design to accommodate a high operating load.
The AFW system actuates automatically in response to specific plant conditions. The AFW system is capable of supplying feedwater to the steam generators during normal unit startup, shutdown and hot standby conditions.
One pump at full flow is sufficient to remove decay heat and cool the unit to residual heat removal (RHR) entry conditions.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Point Beach Nuclear Plant 05000266 YEAR
Previous Similar Events
A review of LERs submitted in the past three years, associated with requirement 10 CFR 50.73(a)(2)(i)(A) "the completion of any nuclear plant shutdown required by the plant's Technical Specifications", having a cause of procedural inadequacy, was conducted. No similar events were identified.
Failed Components Identified None