05000336/LER-2014-007
| Millstone Power Station Unit 2 | |
| Event date: | 07-26-2014 |
|---|---|
| Report date: | 09-24-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| LER closed by | |
| IR 05000245/2015004 (4 February 2016) | |
| 3362014007R00 - NRC Website | |
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1. EVENT DESCRIPTION
On July 26, 2014 at 1411 hours0.0163 days <br />0.392 hours <br />0.00233 weeks <br />5.368855e-4 months <br />, while in operating mode 1, at 100% power, Millstone Power Station Unit 2 (MPS2) operators commenced an orderly shutdown of MPS2 since the turbine driven auxiliary feedwater (TDAFW) pump repairs and required testing would not be completed within the time frame required by Technical Specification (TS) Action Statement (TSAS) 3.7.1.2 action c.
MPS2 TS 3.7.1.2 requires three auxiliary feedwater pumps be operable in operating modes 1, 2 and 3. TSAS 3.7.1.2 action c was entered on July 23 at 1458 hours0.0169 days <br />0.405 hours <br />0.00241 weeks <br />5.54769e-4 months <br /> to support planned surveillance testing of the TDAFW pump. Included in the planned surveillance tests was the performance of an inservice test (1ST) of the recirulating check valve in accordance with station procedures. The recirculation flow measured during the surveillance was less than the minimum acceptable flow rate. The cause of the surveillance test failure of the TDAFW pump could not be determined, and then the repair and retesting activities could not completed within the allowed TSAS time.
Therefore, the operators commenced an orderly shutdown of MPS2 at 1411 hours0.0163 days <br />0.392 hours <br />0.00233 weeks <br />5.368855e-4 months <br /> on July 26.
MPS2 entered operating mode 3 (hot standby) at 1719 hours0.0199 days <br />0.478 hours <br />0.00284 weeks <br />6.540795e-4 months <br /> and operating mode 4 (hot shutdown) at 0738 hours0.00854 days <br />0.205 hours <br />0.00122 weeks <br />2.80809e-4 months <br /> on July 27 thus completing the shutdown as required by the TSAS. All safety systems and equipment functioned as expected. Subsequently, during complex trouble shooting activities a piece of foreign material was found lodged in the flow restricting orifice of the TDAFW pump minimum recirculation line.
Following the removal of the foreign material and additional inspection activities, the TDAFW pump was retested and satisfactorily passed the required TS surveillance test. TS LCO 3.7.1.2 action c was exited on July 29th at 1334 hours0.0154 days <br />0.371 hours <br />0.00221 weeks <br />5.07587e-4 months <br />, allowing restart of MPS2.
This event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(A) - The completion of any nuclear plant shutdown required by the plant's technical specifications.
Background Information:
For operating modes 1, 2 and 3, MPS2 TS 3.7.1.2 action c requires if one AFW pump is inoperable, restore the pump to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If this action is not met, the unit must be in at least hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in hot shutdown within the following 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
2. CAUSE
The direct cause of the shutdown of MPS2 was the inability to identify the cause of the surveillance test failure, and complete the repair and retesting activities within the allowed TSAS time.
Subsequent troubleshooting found a piece of foreign material inside the TDAFW recirculation orifice.
3. ASSESSMENT OF SAFETY CONSEQUENCES
The shutdown of MPS2 in accordance with TSAS 3.7.1.2 action c was conducted in an orderly controlled manner. All safety equipment operated as designed and as expected. The TDAFW pump safety function is to provide flow to the steam generators for decay heat removal. The minimum recirculation line provides recirculation flow for pump cooling during pump operation with flow to the steam generators isolated. As part of the pump in service testing program, the pump is operated, isolated from the steam generators, discharging through the recirculation flow path. The parameters of pump flow, speed and differential pressure are compared to previous data and the pump design performance curve to assess pump performance. With the debris partially blocking the orifice, the flow resistance in the test configuration had changed. This prevented the establishment of the normal testing configuration, however, it had no adverse impact on the ability of the pump to perform its safety function of feeding the steam generators. Although there was reduced flow through the recirculation line, the flow in the recirculation line was sufficient to provide adequate cooling of the pump.
4. CORRECTIVE ACTION
The foreign material was removed, the TDAFW pump was retested and satisfactorily passed the required TS surveillance test. Additional inspection activities did not find any additional foreign material. Additional corrective actions are being taken in accordance with the station's corrective action program.
5. PREVIOUS OCCURRENCES
- LER 2012-002-00, Completion of plant shutdown required by technical specifications, (ultimate heat sink TS 3.7.11)
- LER 2014-001-00, Completion of plant shutdown required by technical specifications, (pressurizer heater failure, TS 3.4.4) 6. Energy Industry Identification System (EIIS) codes
- Auxiliary feedwater system — BA
- TDAFW pump — TRB, P
- Motor driven AFW pump — MO, P
- Steam generator — SG —