05200025/LER-2023-002, Automatic RPS Actuation Durin9 Mode 1 Due to Incorrect Relay Settings Caused by Less than Adequate Questioning Attitude, Validation of Assumptions, and Interface/Guidance
| ML23135A768 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 05/15/2023 |
| From: | Martino P Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| ND-23-0374 LER 2023-002-00 | |
| Download: ML23135A768 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 0252023002R00 - NRC Website | |
text
~ Southern Nuclear May 15, 2023 Patrick Martino Site Vice President, Vogtle Unit 3 7825 River Road Waynesboro, Georgia 30830 706 848 6602 tel ND-23-0374 10 CFR 50.73(a)(2)(iv)(A)
Docket No.:
52-025 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Southern Nuclear Operating Company Vogtle Electric Generating Plant (VEGP)- Unit 3 Licensee Event Report 2023-002-00 Automatic Reactor Protection System Actuation During Mode 1 Due to Incorrect Relay Settings Caused by Less Than Adequate Questioning Attitude, Validation of Assumptions. and Interface/Guidance Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A), Southern Nuclear Operating Company is submitting the enclosed Licensee Event Report for VEGP Unit 3.
This letter contains no regulatory commitments. If you have questions regarding the enclosed information, please contact Will Garrett at (706) 848-7154.
Respectfully submitted,
~.a./--
Patrick A. Martino Site Vice President, Unit 3 PAM/NBC/sfr
Enclosure:
Unit 3 Licensee Event Report 2023-002-00
Patrick Martino Site Vice President, Vogtle Unit 3 7825 River Road Waynesboro, Georgia 30830 706 848 6602 tel cc:
Regional Administrator, Region ll VPO Project Manager Senior Resident Inspector - Vogtle 3 & 4
Vogtle Electric Generating Plant - Unit 3 Licensee Event Report 2023-002 Automatic Reactor Protection System Actuation During Mode 1 Due to Incorrect Relay Settings Caused by Less Than Adequate Questioning Attitude, Validation of Assumptions, and Interface/Guidance Enclosure Unit 3 Licensee Event Report 2023-002-00
Abstract
On March 15, 2023, at 2157 EDT with Vogtle Electric Generating Plant (VEGP) Unit 3 in Mode 1 at 18 percent power, during startup testing, the Reactor Protection System automatically actuated. The operators responded timely by ensuring plant stability, with decay heat removal accomplished by steam generator power operated relief valves. The cause of the event was incorrect protective relay settings on Medium Voltage Switchgear buses ES-4 and ES-6, due to less than adequate questioning attitude, validation of assumptions, and interface/guidance. The corrective actions for this event include the proper setting of the protective relays for buses ES-4 and ES-6 and the revision of guidance for issuing work instructions to include a statement to ensure that the scope of work includes those items listed as additional equipment when multiple components are included in a single work order. This event is reportable under 10 CFR 50. 73(a)(2)(iv)(A) as an automatic actuation of the Reactor Protection System. VEGP Units 1, 2, and 4 were unaffected by this event.
EVENT DESCRIPTION
050 052 I
- 2. DOCKET NUMBER
- 3. LER NUMBER 00025 I
YEAR SEQUENTIAL REV NUMBER NO.
~-I 002 1-G On March 15, 2023, at 2157 EDT with Vogtle Electric Generating Plant (VEGP) Unit 3 in Mode 1 at 18 percent power, during startup testing, the Reactor Protection System (RPS) [EIIS: JC] automatically actuated. The initiating event was a Unit 3 main turbine [EIIS: TA/ TRB] trip due to a differential trip of the excitation transformer protective relays [EIIS: EL/
87). After the turbine trip, the fast bus transfer function failed on non-safety related alternating current (AC) power buses ES-4 and ES-6 [EIIS: EA/ BU] due to incorrect protective relay settings [EIIS: EA/ RL Y]. The loss of voltage on the affected AC power buses resulted in the loss of two (2) of the four (4) Reactor Coolant Pumps (RCPs) [EIIS: AB/ P]. The loss of these RCPs initiated the RPS actuation. There were no structures, systems, or components that were inoperable at the beginning of the event that contributed to the event. This event is reportable under 10 CFR 50. 73(a)(2)(iv)(A) as a condition that resulted in automatic actuation of the RPS.
EVENT ANALYSIS
The cause of the RPS actuation was incorrect settings on Schweitzer Engineering Laboratories protective relays (SEL 451) on Medium Voltage Switchgear buses ES-4 and ES-6, due to less than adequate questioning attitude, validation of assumptions, and interface/guidance. Changes to the relay settings for buses ES-4 and ES-6 were being implemented by Maintenance under one (1) work order. Work Management specifically identified bus ES-1 in the work order scope. The relays for buses ES-4 and ES-6 were included as additional equipment in the work order, but they were not included in the work scope. As a result, the implementation of the design change for the relay settings was only implemented on the relay for bus ES-1. Consequently, settings for relays on buses ES-4 and ES-6 were not changed as intended by the work order.
This resulted in failure of the fast bus transfer function due to the relay settings, resulting in the loss of voltage to two (2)
RCPs.
SAFETY ASSESSMENT
There were no safety consequences due to this event because the automatic actuation function of the RPS maintained the plant in a safe condition. The operators responded timely by ensuring plant stability and decay heat was removed by steam generator power operated relief valves [EIIS: SB / PCV]. All safety systems functioned as expected as a result of the event.
VEGP Units 1, 2, and 4 were unaffected by this event.
CORRECTIVE ACTIONS
- The settings were corrected for protective relays for Medium Voltage Switchgear buses ES-4 and ES-6, which were not included in the scope of work in the original work order. Prior to correction of the relay settings, Medium Voltage Switchgear buses ES-4 and ES-6 were aligned to the Reserve Auxiliary Transformers during subsequent testing to place the main generator on-line. This alignment avoids the need for the fast-bus transfer function, if a main generator lockout were to occur.
- Guidance for issuing work instructions will be revised to include a statement that ensures that the scope of work includes items listed as additional equipment, when multiple components are worked under a single work order. This is expected to be completed by June 13, 2023.
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