05000348/LER-2022-001, Outdated Relay Settings Resulted in an Automatic Reactor Trip After a Floor Tile Was Dropped in High Voltage Switch House
| ML22273A139 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 09/30/2022 |
| From: | Erb D Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-22-0767 LER 2022-001-00 | |
| Download: ML22273A139 (4) | |
| 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 10 CFR 50.73(a)(2)(iv), System Actuation |
| 3482022001R00 - NRC Website | |
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3/4a: Southern Nuclear Regulatory Affairs Date:
September 30, 2022 3535 Colonnade Parkway Birmingham. AL 35243 205 992 5000 Docket Nos.: 50-348 Nl-22-0767 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Joseph M. Farley Nuclear Plant-Unit 1 Licensee Event Report 2022-001-00 Outdated Relay Settings Resulted in an Automatic Reactor Trip After a Floor Tile was Dropped in High Voltage Switch House Ladies and Gentlemen: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 Unit 1.
This letter contains no NRC commitments. If you have any questions, please contact Gene Surber at 334.661.2265.
. Erb Vice President - Farley DE/kmo/cbg Enclosure: Unit 1 licensee Event Report 2022-001-00 cc:
Regional Administrator, Region II NRR Project Manager - Farley Nuclear Plant Senior Resident Inspector - Farley Nuclear Plant RTYPE: CFA04.054
Joseph M. Farley Nuclear Plant - Unit 1 Licensee Event Report 2022-001-00 Outdated Relay Settings Resulted in an Automatic Reactor Trip After a Floor Tile was Dropped in High Voltage Switch House Enclosure Unit 1 Licensee Event Report 2022-001-00
Abstract
At 1258 CDT on August 3, 2022, with Joseph M. Farley Nuclear Plant (FNP) Unit 1 in Mode 1 at 100 percent power, the reactor automatically tripped following a generator trip and subsequent turbine trip signal. A floor tile was dropped in the high voltage switch house resulting in a relay actuation that electrically isolated Bus 1 in the 230kV switchyard. The "B" train emergency safeguards (ES) bus lost power along with 18, 1C, and 1E non safety related 4160V busses. The 1A 4160V non safety bus did not fast bus transfer to its alternate power supply, which along with isolation of the 230kV Bus 1, resulted in all Reactor Coolant Pumps being deenergized. Residual heat was removed by natural circulation via the atmospheric relief valves.
The 1 B emergency diesel automatically actuated due to the loss of power to the "B" train ES bus. In addition, the Auxilliary Feedwater System (AFW) automatically started as expected in response to the reactor trip.
Corrective actions include calibrating the associated relays following revision to calculations and relay sheets. Additionally, the design calculation change process will be revised to ensure plant impacts are incorporated into plant procedures.
This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) due to the automatic actuation of multiple systems listed in 10 CFR 50.73(a)(2)(iv)(B). FNP Unit 2 was not affected during this event.
EVENT DESCRIPTION
On August 3, 2022, at 1258 CDT, while Joseph M. Farley Nuclear Plant (FNP) Unit 1 was in Mode 1 at 100 percent power, a transmission worker moving floor tiles in the high voltage switch house dropped a floor tile creating vibration near a relay panel [EEIS: FK] which actuated relay TD-50 [EEIS: FK / 62]. Relay TD-50 is designed to isolate bus 1 of the 230kV switchyard upon a fault. For Unit 1 this protection scheme resulted in the loss of the "B" Train Emergency Safeguards (ES) bus [EEIS: EB] and Non Safety 4160V Busses 18 / 1C / 1E. Relays KD-10 (Distance Relay} [EEIS: FK/21) and KC-2 (Current Relay} [EEIS: FK / 67) are in series to protect the main generator from overcurrent. KD-10 actuated per design when the 230kv bus 1 lost voltage. KC-2 is designed to actuate on high current through the generator output breakers. It was determined post trip that KC-2 was set improperly. It was determined that while online at 100% power, KC-2 was in an actuated state because the actual current was above its setpoint. Thus, when KD-1 O actuated the circuit was completed to send a trip signal to the main generator. The generator trip and subsequent turbine trip [EEIS:JI/EL] resulted in an automatic reactor trip [EEIS:AA/JC). The 1B emergency diesel [EEIS: EK] automatically started upon the loss of power to the "B" train ES bus. Subsequent to the automatic actuation of the reactor protection system (RPS), the auxiliary feedwater (AFW) pumps [EEIS: BA] automatically started as expected. The 1 A 4160V non safety bus did not fast bus transfer to its alternate power supply, which along with isolation of the 230kV Bus 1, resulted in all Reactor Coolant Pumps [EEIS: AB] being deenergized. Unit 1 residual heat was removed via natural circulation via the atmospheric relief valves immediately following the event.
EVENT ANALYSIS
The cause of this event was a combination of a human performance event and a legacy relay setting error. The relay actuations from the dropped floor tile, by itself, would not have resulted in a reactor trip. The KD-10 relay was actuated upon the loss of the 230kV Bus 1, however had KC-2 been set properly, the generator trip and subsequent reactor trip would not have occurred. The relay values of KC-2 had not been updated following a design calculation change, and the design calculation change process did not identify when an update to associated relay settings sheets were required.
REPORTABILITY AND SAFETY ASSESSMENT
There were no safety consequences as result of this event. The operating crew responded appropriately to the event.
This event was within the analysis of the UFSAR Chapter 15. Additionally, no radiological release occurred due to this event. This event is reportable under 10 CFR 50.73(a}(2}(iv)(A) due to the automatic actuation of the RPS, the 18 Emergency Diesel, and the AFW system as identified in 10 CFR 50.73(a)(2)(iv)(8}.
CORRECTIVE ACTIONS PLANNED OR COMPLETED
- 1. Revise Design Calculation and update relay setpoint sheets.
- 2. Calibrate KC-2 relay to new setpoints.
- 3. Revise the governing procedures for the design calculation change process.
- 4. Incorporated improved work control zones and labeling in the switchyard relay house.
PREVIOUS SIMILAR EVENTS
There were no events from the last three years with either the same or similar cause to this event.
NRC FORM 368A (08-2020)
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