05000306/LER-2021-001, Turbine Driven Auxiliary Feedwater Pump Actuation Signal Due to Procedure Error
| ML21322A283 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 11/18/2021 |
| From: | Domingos C Northern States Power Company, Minnesota, Xcel Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-PI-21-043 LER 2021-001-00 | |
| Download: ML21322A283 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3062021001R00 - NRC Website | |
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ENCLOSURE 1 PRAIRIE ISLAND NUCLEAR GENERATING PLANT LICENSEE EVENT REPORT 50-306/2021-001-00 2 pages follow
Abstract
On October 3, 2021, with Prairie Island Nuclear Generating Plant (PINGP) Unit 2 in Cold Shutdown, the 22 Turbine Driven Auxiliary Feedwater (AFW) Pump received a valid actuation signal. While performing the prerequisite checklists for Surveillance Procedure (SP) 2083A Unit 2 Integrated SI Test with a Simulated Loss of Offsite Power Train A, the Train B 22 Turbine Driven Auxiliary Feedwater (AFW) Pump selector switch in the Main Control Room was placed in Shutdown Auto from Manual. This, combined with having the Non-Safety Related 4160 Volt buses 21 and 22 isolated for maintenance, completed the automatic start signal. The turbine and pump did not turn because the equipment was out of service with the steam supply valves closed.
This event is reportable under 10CFR 50.73(a)(2)(iv)(A) due to a valid Pressurized Water Reactor Auxiliary Feedwater actuation signal.
There was no impact on the ability to maintain safe shutdown conditions. The system operated as designed.
The cause of this event was a latent procedure error in SP 2083A.
The corrective action was an update to the SP 2083A prerequisite checklist to place the 22 Turbine Driven AFW Pump selector switch to Manual.
EVENT DESCRIPTION
On October 3, 2021, the Prairie Island Nuclear Generating Plant (PINGP) Unit 2 was in Mode 5, Cold Shutdown, at 0 percent power with Non-Safety Related 4160 Volt buses 21 and 22 isolated for maintenance. At 1525 CDT, the 22 Turbine Driven Auxiliary Feedwater (AFW) Pump received an unplanned actuation signal while performing the prerequisite checklists of Surveillance Procedure (SP) 2083A Unit 2 Integrated SI Test with a Simulated Loss of Offsite Power Train A when the 22 Turbine Driven AFW Pump selector switch in the Main Control Room was placed in Shutdown Auto from Manual.
This event is reportable under 10CFR 50.73(a)(2)(iv)(A) due to a valid Pressurized Water Reactor Auxiliary Feedwater actuation signal, per NUREG 1022, Revision 3.
EVENT ANALYSIS
The 22 Turbine Driven AFW Pump is a part of the PINGP AFW System (EIIS CODE: BA). The AFW System automatically supplies feedwater to the steam generators (SG) to remove decay heat from the Reactor Coolant System upon the loss of normal feedwater supply. The AFW system is configured into two redundant trains. One train has a turbine driven AFW pump; the other has a motor driven AFW pump. One automatic start signal for the turbine driven AFW Pump is the loss of both non-safety related 4160 Volt buses that provide power to the Main Feedwater (MFW) pumps. A loss of power for both MFW pumps will start the turbine driven AFW pump to ensure that at least one SG contains enough water to serve as the heat sink for reactor decay heat and sensible heat removal following the reactor trip.
With Non-Safety Related 4160 Volt buses 21 and 22 isolated for maintenance, placing the 22 Turbine Driven AFW Pump selector switch in Shutdown Auto completed the automatic start signal causing the associated 22 Turbine Driven AFW Pump Steam Block Valve to open. The turbine and pump did not turn because the equipment was out of service with the steam supply valves closed. The 22 Turbine Driven AFW Pump Steam Block Valve then returned to the closed position on a Low Pump discharge pressure signal.
ASSESSMENT OF SAFETY CONSEQUENCES
The actuation signal for the 22 Turbine Driven AFW Pump did not challenge the ability to maintain safe shutdown conditions. There were no radiological, environmental, or industrial impacts associated with this event. The health and safety of the public and site personnel were not impacted during this event.
CAUSE OF THE EVENT
The cause of this event was a latent procedure error in SP 2083A from when the procedure was changed from testing both trains of the system to testing each of the trains separately.
CORRECTIVE ACTIONS
Operations updated the SP 2083A prerequisite checklist to place the 22 Turbine Driven AFW Pump selector switch to Manual.
PREVIOUS SIMILAR EVENTS
No previous similar events have occurred at PINGP in the prior 3 years.