ENS 47321
ENS Event | |
|---|---|
12:27 Oct 5, 2011 | |
| Title | Two Loops of Reactor Coolant System (Rcs) Were Declared Inoperable |
| Event Description | Unit 2 was shut down at 1048 CDT on October 4, 2011 due to 22 Reactor Coolant Pump (RCP) low seal leak off flow. At 0727 CDT on October 5, 2011 with Unit 2 in Mode 4 and 22 RCP secured, 21 RCP was also secured due to low seal leak off flow.
It was determined that the station would not consider RHR [residual heat removal] available for decay heat removal per Technical Specification (TS) due to a procedural issue related to component cooling shutdown lineups. RCS temperature is being maintained stable in Mode 4 between 320 and 340 degrees Fahrenheit using natural circulation and the steam dump to the condenser. No operations were permitted that would have caused introduction into the RCS, coolant with boron concentration less than required to meet the Shutdown Margin. At approximately 1329 CDT, 21 RCP was restarted after the flow transmitters were vented and 21 RCP seal leak off flow was determined to be acceptable. The RHR procedural issue has been resolved. Per TS LCO 3.4.6, 'Two loops consisting of any combination of RCS loops and residual heat removal (RHR) loops shall be OPERABLE, and one loop shall be in operation.' This condition is reportable as an event or condition that could have prevented fulfillment of a safety function under 10CFR 50.72(b)(3)(v)(B). During this event, RHR could not be credited because the utility was not able to valve in component cooling water to a SFP heat exchanger due to procedural issues. With the restart of 21 RCP and shutdown cooling water alignment, TS 3.6.4 A and B statements have been met and exited. 21 RCP loop in operation and 22 RHR is operable and can be aligned for shutdown cooling. Both Unit 2 EDG's are available and offsite power is normal electrical lineup. The licensee is no longer in any TS LCO statements. The NRC Resident Inspector has been notified.
An eight hour report (EN#47321) per 10CFR 50.72(b)(3)(v)(B) was conservatively reported because both trains of Residual Heat Removal (RHR) system and both trains of Reactor Coolant System (RCS) were thought to be unavailable. Additional review indicated that 21 RCP and 22 RCP were undamaged, functional, and available for loop operation; therefore, there was no loss of safety function as RCPs were available. The station evaluated 21 and 22 RCP seal leak off flow performance and subsequently restarted 21 RCP and restored forced cooling. The 21 RCP seal leak off flow has remained stable in the acceptable range. 21 RCP was available throughout this evolution. If needed in Mode 4, 22 RCP was also available. The procedures that were in place and available to the operators prior to 1320 CDT on October 5, 2011, would have allowed RHR operation; however, to supply RHR to Unit 2, Unit 1 would have entered an LCO (for supplying Component Cooling (CC) water to the Spent Fuel Pool (SFP) heat exchangers) to maintain RHR's safety function. After 1320 CDT, procedure revisions allowed operation of RHR without an associated Unit 1 LCO entry. RHR remained operable throughout this evolution. In summary, a loss of safety function for both trains of RHR and RCS did not exist and the 50.72(b)(3)(v)(B) report (EN 47321) is retracted. The NRC Resident Inspector has been informed. R3DO(Phillips) notified. |
| Where | |
|---|---|
Prairie Island  Minnesota (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | |
| Time - Person (Reporting Time:+3.38 h0.141 days <br />0.0201 weeks <br />0.00463 months <br />) | |
| Opened: | Jack Kempkes 15:50 Oct 5, 2011 |
| NRC Officer: | Joe O'Hara |
| Last Updated: | Oct 7, 2011 |
| 47321 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Hot Shutdown (0 %) |
| After | Hot Shutdown (0 %) |