05000341/LER-2022-002, Unexpected High Pressure Coolant Injection Turbine Trip
| ML22187A109 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 07/06/2022 |
| From: | Peter Dietrich DTE Electric Company |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NRC-22-0025 LER 2022-002-00 | |
| Download: ML22187A109 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3412022002R00 - NRC Website | |
text
July 6, 2022 NRC-22-0025 U.S. Nucleal' Regulat01y Commission Attention: Document Control Desk Washington, DC 20555-0001 Penni 2 Power Plant NRC Docket No. 50-341 NRC License No. NPF-43
Subject:
Licensee Event Repo1i (LER) No. 2022-002 Peter Dietrich Senior Yice Pn5ident and Chief Nuclear Officer DTE Electric Company 6400 ~. Dixie Highway, Newport, MI 48166 Tel:
734.586.4153 Email: peter.dietrich@dteenergy.com DTE 10 CFR 50.73 Pursuant to 10 CFR 50.73(a)(2)(v)(D), DTE Electric Company (DTE) is subinitting LER No.
2022-002, Unexpected High Pressure Coolant Injection Turbine Trip.
No new commitments are being made in this submittal.
Should you have any questions or require additional inf01mation, please contact Mr. Eric Frank, Manager -Nuclear Licensing, at (734) 586-4772.
Sincerely, Eric Olson Site Vice President for Peter Dietrich Senior Vice President and Chief Nuclear Officer Enclosure: Licensee Event Repo1t No. 2022-002, Unexpected High Pressure Coolant Injection Turbine Trip cc:
NRC Project Manager NRC Resident Office Regional Adininistrator, Region III
Enclosure to NRC-22-0025 Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43 Licensee Event Report (LER) No. 2022-002 Unexpected High Pressure Coolant Injection Turbine Trip
Abstract
On May 11, 2022, the High Pressure Coolant Injection (HPCI) turbine unexpectedly experienced an overspeed trip during performance of surveillance 24.202.01 "HPCI Pump and Valve Operability Test At 1025 PSI". The cause was the HPCI Turbine Magnetic Pick-Up Speed Element (E41N212) was found shorted, breaking the speed feedback circuit to the HPCI Speed Controller. The HPCI Turbine Magnetic Pick-Up Speed Element (E41 N212) was replaced on 05/12/2022 and HPCI 24.202.01 surveillance was completed satisfactorily on 05/16/2022.
An 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Event Notification 55894 was reported to the NRC operations center per 10 CFR 50.72(b)(3)(v)(D). This report is submitted per 10 CFR 50.73(a)(2)(v)(D).
INITIAL PLANT CONDITIONS
Mode - 1 Reactor Power - 10 Percent There were no structures, systems, or components (SSCs} that were inoperable at the start of this event that contributed to this event. Automatic Depressurization System (ADS} [RV] and Reactor Core Isolation Cooling (RCIC}[BN] were operable during the event.
DESCRIPTION OF THE EVENT On May 11, 2022 at 1814 the plant was in Mode 1 performing start up activities. A High Pressure Coolant Injection (HPCI)
[BJ] surveillance was in progress via surveillance 24.202.01 "HPCI Pump and Valve Operability Test at 1025 PSI." The HPCI turbine tripped on a mechanical overspeed due to failure of the HPCI Turbine Magnetic Pick-Up Speed Element (E41N212}. Operations noted the HPCI Turbine Steam Isolation Valve (E4100F067} and the HPCI/RCIC Test Pressure Control Valve (E41 00F011 } were opening and closing unexpectedly. HPCI is designed to automatically restart when turbine speed drops below the mechanical over speed trip setpoint.
Troubleshooting of the system shows the system restarted twice following the initial overspeed trip before HPCI was manually tripped. Troubleshooting determined that the HPCI Turbine Magnetic Pick-Up Speed Element (E4100N212}
was shorted, breaking the speed feedback circuit to the HPCI Speed Controller. Troubleshooting also identified the HPCI Pump Discharge Pressure Switch (E41 00N027}, which controls the HPCI Minimum Flow Valve (E4150F012) was found to be out of tolerance low, causing the HPCI minimum flow valve (E4150F012) to cycle open and closed.
There is no evidence the condition of the shorted HPCI Turbine Magnetic Pick-Up Speed Element (E4100N212) or the HPCI Pump Discharge Pressure Switch (E41 00N027) low out of tolerance conditions existed prior to the overspeed trip event on 05/1 1/2022. This is based on the fact the HPCI system performed as expected during surveillance testing 24.202.02 HPCI Flow Rate Test At 165 PSI Reactor Steam Pressure on 05/09/2022 and HPCI did not exhibit abnormal behavior prior to the start of 24.202.01 "HPCI Pump and Valve Operability Test at 1025 PSI" on 05/11/2022.
The HPCI Turbine Magnetic Pick-Up Speed Element (E4100N212) was replaced and the HPCI Pump Discharge Pressure Switch (E41 00N027) was successfully calibrated into tolerance and HPCI was restored to operable status following satisfactorily performance of 24.202.01 HPCI Pump and Valve Operability at 1025 Rx PSIG" on 05/16/2022.
Prior to the event, during the refueling outage, the HPCI turbine internal inspection was performed; which, included removing HPCI Turbine Magnetic Pick-Up Speed Element (E4100N212). The Post Maintenance Test for this work included performing both 24.202.02 "HPCI Flow Rate Test At 165 PSI Reactor Steam Pressure" and 24.202.01 "HPCI Pump and Valve Operability at 1025 Rx PSIG". Procedure 24.202.02 was satisfactorily completed on 05/09/2022. On 05/11/2022, the HPCI turbine unexpectedly experienced an overspeed trip during performance of surveillance 24.202.01.
Troubleshooting determined the HPCI Turbine Magnetic Pick-Up Speed Element (E41 N212) had failed. The failed speed element was replaced and HPCI 24.202.01 surveillance was completed satisfactorily on 05/1 6/2022.
An 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Event Notification 55894 was reported to the NRC operations center per 10 CFR 50.72(b}(3)(v)(D). This report is submitted per 10 CFR 50.73(a)(2)(v)(D).
SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS
During the time HPCI was inoperable, the RCIC system remained OPERABLE for high pressure injection in the event of an emergency. The Standby Feedwater (SBFW) [SJ] system was also available for high pressure injection. Additionally, the Automatic Depressurization System (ADS) was available to reduce reactor pressure to within the capabilities of the low pressure Emergency Core Cooling Systems (ECCS) [BO][BM]. TS 3.5.1 allows HPCI to be taken out of service for up to 14 days provided that RCIC is available. The duration of the HPCI inoperability, although unplanned, was within the allowable out of service time. HPCI is required for design basis accidents such as a loss of coolant accident (LOCA). No accidents or transients requiring HPCI occurred or were in progress during the HPCI inoperability.
Based on this, the safety significance of this event is low. There were no radiological releases associated with this event.
CAUSE OF THE EVENT
The direct cause was the failed HPCI Turbine Magnetic Pick-Up Speed Element (E4100N212). The magnetic pick-up switch was found shorted, breaking the speed feedback circuit to the HPCI Speed Governor. This resulted in a loss of speed indication to the HPCI governor (E4100K200) controller "HPCI Turbine Governor (EG-M) speed controller and HPCI overspeed turbine trip. The speed sensor was replaced and HPCI 24.202.01 surveillance was completed satisfactorily, confirming the speed sensor was the failed component.
CORRECTIVE ACTIONS
The failed HPCI Turbine Magnetic Pick-Up Speed Element (E4100N212) was replaced and the HPCI Pump Discharge Pressure Switch (E41 00N027) was recalibrated to within tolerance.
PREVIOUS OCCURRENCES
There have been previous occurrences of unplanned HPCI inoperability in the past several years, for example LERs 2018-005 dated September 2018 and 2019-004 dated September 2019. However, those occurrences were due to a support system, the Mechanical Draft Cooling Towers (MDCT), not being able to support operability of the Division 2 Emergency Equipment Cooling Water (EECW) system which is required for the operability of the HPCI room cooler.
Therefore, the corrective actions taken to resolve those previous occurrences would not have prevented the issue described in this LER.
LER 21-002 Rev.1, dated March 2022, the unplanned inoperability of the HPCI system due to an inverter circuit failure had an unknown cause but was most likely due to a voltage transient. Components in the system were found shorted.
The failure mechanism of the inverter and the sequencer failures were caused by a voltage transient on the DC bus. This transient was created from an unknown source either electrically or magnetically coupled to the supply cables of the devices. Therefore, the corrective actions taken to resolve this previous occurrence would not have prevented the issue described in this LER.
NUMBER I YEAR SEQUENTIAL 1
002 1-REV NO.
0 In addition, August 2021 HPCI was declared inoperable (EN 55403) for a HPCI failure due to poor connections associated with the flow controller. EN55403 was recently retracted as HPCI was determined to be operable. The cause and corrective actions associated with EN55403 event were reviewed from the perspective of this event being reported in this LER and it was detennined that the two events were independent. Therefore, the corrective actions taken to resolve these issues would not have prevented the issue described in this LER. Page 4
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