05000387/LER-2023-001, Inadvertent Contact Between Relay Cover and Relay Trip Contacts Resulted in Automatic Actuation of the ‘B’ Emergency Diesel Generator
| ML23142A269 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 05/22/2023 |
| From: | Casulli E Susquehanna, Talen Energy |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| PLA-8068 LER 2023-001-00 | |
| Download: ML23142A269 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B), System Actuation |
| 3872023001R00 - NRC Website | |
text
Edward Casulli Susquehanna Nuclear, LLC
SiteVicePresident 769 Salem Boulevard Berwick, PA 18603 Tel. 570.542.3795 Fax 570.542.1504 Edward.Casulli@TalenEnergy.com May 22, 2023 Attn: Document Control Desk 10 CFR 50.73 U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 SUSQUEHANNA STEAM ELECTRIC STATION LICENSEE EVENT REPORT 50-387(388)/2023-001-00 UNIT 1 LICENSE NO. NPF-14 UNIT 2 LICENSE NO. NPF-22 PLA-8068 Docket No. 50-387 and 50-388 Attached is Licensee Event Report (LER) 50-387(388)/2023-001-00. The LER reports an event in which inadvertent contact between a relay cover and the relay trip contacts resulted in an automatic actuation of the B Emergency Diesel Generator. This condition is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event or condition that resulted in manual or automatic actuation of any system listed in 10 CFR 50.73(a)(2)(iv)(B).
There were no actual consequences to the health and safety of the public as a result of this event.
This letter contains no new or revised regulatory commitments.
E. Casulli Attachment: LER 50-387(388)/2023-001-00 Copy: NRC Region I Mr. C. Highley, NRC Senior Resident Inspector Ms. A. Klett, NRC Project Manager Mr. M. Shields, PA DEP/BRP TALEN~
ENERGY
Abstract
On March 23, 2023, while reinstalling a relay cover on Engineered Safeguard System (ESS) Bus 2A202, inadvertent contact was made between the target reset lever on the relay cover and the relay trip contacts. This resulted in a trip of all 4.16 kV breakers on the 2B ESS Bus 2A202, an ESS bus lockout, and automatic start of the B Emergency Diesel Generator (EDG). This condition is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event or condition that resulted in manual or automatic actuation of any system listed in 10 CFR 50.73(a)(2)(iv)(B). This event was also reported via Event Notification 56430 in accordance with 10 CFR 50.72(b)(3)(iv)(A).
The cause of the event was a momentary loss of focus on the relay target reset lever during reinstallation of the relay cover.
This cause was attributed to a human performance error. Additional investigation concluded the potential impacts of an inadvertent error associated with the relay reinstallation activities were not adequately mitigated. Corrective actions included performing accountability per station procedures and planned procedure revisions to include continuous use checklists identifying removal and restoration work steps associated with relays that have the potential to trip protective devices.
There were no actual consequences to the health and safety of the public.
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CONDITIONS PRIOR TO EVENT
Unit 1 - Mode 1, approximately 100 percent Rated Thermal Power (RTP)
Unit 2 - Mode 5, zero percent RTP The described activity was performed during the Division 2 electrical maintenance outage with Division 1 systems protected. There were no structures, systems, or components that were inoperable at the start of the event and contributed to the event.
EVENT DESCRIPTION
On March 23, 2023, while reinstalling a relay cover on Engineered Safeguard System (ESS) [EIIS System Code: B] Bus 2A202 [EIIS System/Component Code: E/BU], inadvertent contact was made between the target reset lever on the relay [EIIS Component Code: RLY] cover and the relay trip contacts. This resulted in a trip of all 4.16 kV breakers [EIIS Component Code: BKR] on the 2B ESS Bus 2A202, an ESS bus lockout, and automatic start of the B Emergency Diesel Generator (EDG) [EIIS System/Component Code: EK/DG].
The B EDG operated as expected.
The following timeline demonstrates the sequence of events:
03/23/2023 ~ 15:45: Relay and Test lead technician conducted a pre-job brief for critical relay calibrations on ESS Bus 2A202.
03/23/2023 ~ 16:15 - 17:00: Technicians arrived at the work area and performed a two minute drill. Removal, calibration, and reinstallation of the A-phase bus differential relay was completed.
03/23/2023 ~ 17:00 - 17:30: Removal and calibration activities for the B-phase bus differential relay was completed.
03/23/2023 ~ 17:33: During installation of the relay cover, inadvertent contact was made between the target reset lever on the relay cover and the relay contacts. This resulted in a trip of the 2B Bus lockout relays which opened all the bus supply breakers and started the B EDG.
3/23/23 ~ 17:37: All work was stopped and the Unit 2 control room was contacted.
This condition is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event or condition that resulted in manual or automatic actuation of any system listed in 10 CFR 50.73(a)(2)(iv)(B). This event was also reported via Event Notification 56430 in accordance with 10 CFR 50.72(b)(3)(iv)(A).
CAUSE OF EVENT
The cause of the event was a momentary loss of focus on the relay target reset lever during reinstallation of the relay cover. This cause was attributed to a human performance error. Additional investigation concluded the potential impacts of an inadvertent error associated with the relay reinstallation activities were not adequately mitigated.
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ANALYSIS/SAFETY SIGNIFICANCE
Based on engineering analysis of the event, with the failure of one on-site circuit (i.e., B EDG), the three remaining buses could achieve safe shutdown of the operating unit during all design basis accidents, consistent with the design and licensing basis of the plant. There was sufficient redundancy in systems impacted by the failure such that their safety function would still be performed. Safe shutdown was also maintained for Unit 2, which was in Mode 5 for the refueling and inspection outage. Therefore, the electrical power system could have fulfilled its safety function for the condition described.
Accordingly, this event will not be counted as a safety system functional failure in the Reactor Oversight Process Performance Indicator. There were no actual consequences to the health and safety of the public as a result of this event.
CORRECTIVE ACTIONS
Corrective actions included performing accountability per station procedures and planned procedure revisions to include continuous use checklists identifying removal and restoration work steps associated with relays that have the potential to trip protective devices.
COMPONENT FAILURE INFORMATION
Not applicable.
PREVIOUS OCCURRENCES
None.
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