05000348/FIN-2016002-04
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Finding | |
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| Title | Condition Prohibited by Technical Specifications Due to Turbine Driven Auxiliary Feedwater Design Issue |
| Description | On November 20, 2015, the Unit 1 TDAFW pump over sped and tripped on startup during surveillance testing. The licensee determined a previous design change that adjusted the MPU override timer setting from 10 seconds to 600 seconds resulted in a governor controller speed set point conflict that revealed itself during the performance of the test. The licensee implemented the set point change after consulting with the vendor as a corrective action to address previous issues with the setting of the MPU override timer. This new failure mode was not anticipated when the TDAFW pump governor controller MPU timer setpoint was changed in April 2015 on Unit 1, and January 2015 on Unit 2. After the modification was made on each unit, several successful starts were performed to validate the setpoint adjustment before the pumps were returned to service. Additionally, the TDAFW pumps had been successfully started 19 times on Unit 1 and 15 times on Unit 2 for surveillances, post-maintenance testing, and troubleshooting while the condition existed. Once discovered, the licensee implemented another design change to adjust the low idle speed setpoint to minimize the potential for turbine speed overshoot on startup. Enforcement: Farley Unit 1 and 2 Technical Specification (TS) limiting condition for operation (LCO) 3.7.5, Auxiliary Feedwater (AFW) System, required three operable AFW trains while the Unit is in modes 1, 2 or 3. With one AFW pump train inoperable, LCO 3.7.5. Condition B required restoration of the AFW train to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and within 10 days from discovery of failure to meet the LCO. Contrary to this requirement, Unit 1 operated from May 3, 2015, until November 22, 2015, with the Unit 1 turbine driven AFW inoperable. Unit 2 operated from January 10, 2015, until November 22, 2015, with the Unit 2 turbine driven AFW inoperable. A regional senior reactor analyst (SRA) performed a detailed risk evaluation to evaluate the risk increase associated with the condition. No failures occurred on Unit 2, therefore the condition did not result in a risk increase for Unit 2. The evaluation for Unit 1 was performed using the NRC Farley SPAR model with input from the licensees NFPA 805 Fire PRA model for the fire external event risk. The major analysis assumptions for Unit 1 included a 200 day exposure interval, recovery credit for local manual overspeed trip reset evaluated using the NRC SPAR-H human reliability analysis method, and an overspeed trip startup failure probability determined from plant specific data. The dominant risk sequence was a total loss of service water resulting in a plant trip and failure of the motor driven auxiliary feedwater (MDAFW) pumps, with failure of the turbine driven AFW pump due to the overspeed trip condition on startup with failure of the operator to accomplis
overspeed trip reset which would lead to loss of core heat removal and core damage. The result of the detailed risk evaluation was an increase in risk due to the condition of <1.0 E-6/ year. The inspectors concluded that the violation was of very low safety significance (Green) and consistent with a Severity Level IV violation. The NRC exercised enforcement discretion (Enforcement Action EA-16-159) for this violation in accordance with sections 2.2.4.d and 3.5 of the NRCs Enforcement Policy because the impact of the design change was not within the licensees ability to foresee and correct beforehand. The inspectors reached this conclusion due to the number of successful TDAFW pump starts following implementation of the design change and the specific vendor recommendation to adjust the MPU override timer setting to greater than 30 seconds. This issue was entered into the licensees corrective action program as CR 10149716. |
| Site: | Farley  |
|---|---|
| Report | IR 05000348/2016002 Section 4OA3 |
| Date counted | Jun 30, 2016 (2016Q2) |
| Type: | Violation: Green |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | J Munday J Rivera-Ortiz K Miller P Niebaum R Powell |
| Violation of: | Technical Specification |
| INPO aspect | |
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Finding - Farley - IR 05000348/2016002 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Farley) @ 2016Q2
Self-Identified List (Farley)
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