05000348/LER-2023-001, Automatic Reactor Trip Due to DC Ground on Turbine Trip Solenoid
| ML23089A356 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 03/30/2023 |
| From: | Erb D Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-23-0221 LER 2023-001-00 | |
| Download: ML23089A356 (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 |
| 3482023001R00 - NRC Website | |
text
-1/4. Southern Nuclear Date:
March 30, 2023 Docket No.:
50-348 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Delson Erb Vice President - Farley Joseph M. Farley Nuclear Plant - Unit 1 Licensee Event Report 2023-001-00 Joseph M. Farley Nuclear Plant 7388 North State Hwy 9S Colwnbia, Alabama 36319 334.661.2100 tel 334.661.2512 fax dcrb~'southcmco.com NL-23-0221 Automatic Reactor Trip due to DC Ground on Turbine Trip Solenoid Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50. 73(a)(2)(iv)(A), Southern Nuclear Company is submitting the enclosed Licensee Event Report for Unit 1.
This letter contains no NRC commitments. If you have any questions regarding this submittal, please contact Gene Surber at (334) 661-2265.
Rea
$U milled, Delson Erb Vice President-Farley DE/rgs/cbg Enclosure: Unit 1 Licensee Event Report 2023-001-00 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 2023-001-00 Automatic Reactor Trip due to DC Ground on Turbine Trip Solenoid Enclosure Unit 1 Licensee Event Report 2023-001-00
Abstract
At 0956 CST on February 1, 2023, with Joseph M. Farley Nuclear Plant (FNP) Unit 1 in Mode 1 at 100 percent power, the reactor automatically tripped following a turbine trip signal. The turbine tripped when Maintenance personnel connected portable DC ground detection equipment (DC Scout) to the positive terminal of the "B" train Auxiliary Building battery to locate a DC ground. Connecting the DC Scout created a jumper to the normally open contact of the Turbine Trip Solenoid. Operations stabilized the plant in Mode 3 and removed decay heat via steaming to condenser. Auxiliary Feedwater System (AFW) automatically actuated as expected in response to the reactor trip.
Corrective actions include changes to risk mitigation procedures associated with detecting DC grounds and use of portable ground detection equipment.
This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) due to the automatic actuation of the Reactor Protection System (RPS) and AFW system as listed in 10 CFR 50.73(a)(2)(iv)(B). FNP Unit 2 was not affected during this event.
EVENT DESCRIPTION
Es1imalad burden per response lo comply with llis mandalDly c:dledion request eo hows. Repolled lessons laamad are lnCOIJJ(llllllld Into 1111 llcenslng proce9S and fed back lo Industry. Send comments regardng burden esllmate lo lhe FOIA. Lilraly. and lnfonnalion Colec:tions Branch (T-6 A10M). U.S.
Nuclear Ragu1atory Commission, Washilglon, DC 20555-0001, or by email lo lnfocoleds.Rasoun:e@nrc.gov, and lhe 0MB re'liewer at 0MB Office of Information and Regulaloly Affairs, (3150-0104). A1tn: Desk Officer for lhe NUclear Regintory Commission, 725 17th Sll88t INf, Washlnglon, DC 20503; email: dra submlssloo@omb eop IIOY* The NRC may not conduct or sponsor, and a person Is not requted to respond to. a co1ledlon of lhfolmatton unless lhe document requesting or requiring the c:oAdoll displays a c:uminlly valil 0MB contrul number.
- 2. DOCKET NUMBER
- 3. LER NUMBER 348 I
YEAR SEQUENTIAL REV r:=i NUMBER NO.
- - 1 001 1-0 On February 1, 2023, at 0956 CST, while Joseph M. Farley Nuclear Plant (FNP) Unit 1 was in Mode 1 at 100 percent power, maintenance was conducting troubleshooting to identify the source of an Auxilliary Building (AB) "B" Train DC ground. The ground was identified to be on the negative side of the AB Battery [EIIS / EEIS : EJ / BTRY]. When portable ground detection equipment (DC Scout) was connected to the positive terminal of the AB Battery a loss of Electro Hydraulic Control (EHC) [EIIS: TG] oil pressure occurred which resulted in a turbine trip and subsequent reactor trip. During the forced outage it was determined that the DC ground existed on a cable between the AB and Turbine Building associated with the Turbine Trip Solenoid Valve (20-ET) [EIIS / EEIS: TG / SOL]. The 20-ET solenoid valve is normally closed and energizes to open to dump EHC oil from the turbine throttle valves and governor valves. It was confirmed via troubleshooting that when maintenance connected the DC Scout to the AB Battery terminal it created a jumper in the circuit to energize the 20-ET solenoid.
During the plant trip the "1A" 4 kV non emergency bus [EIIS: EA) failed to transfer to the "1A" 4 kV Startup Transformer [EIIS : EB). This resulted in the trip of the "A" Reactor Coolant Pump (RCP) [EIIS / EEIS: AB/ PJ. The "B" and "C" RCPs remained in operation. Additionally, Auxilliary Feedwater System (AFW) [EIIS: BAJ autostarted as expected post reactor trip and maintained feedwater flow to the Steam Generators (EIIS: SB). Main Feed Water (MFW) [EIIS: SJ] and the condenser [EIIS: SG] remained available for post trip decay heat removal.
EVENT ANALYSIS
It was determined that previous unrelated work at penetration 07-155-31 had resulted in damage to cable 1 UYT0001 E [EEIS : CBL4) which feeds the 20-ET solenoid. This damage inside the penetration breach was not visible and had resulted in the AB DC ground alarm. The risk of actuating equipment in the circuit while installing portable ground detection equipment was not known and led to missed opportunities in work planning and risk mitigation. The failure of the bus transfer to occur was determined to be a failure of the Time Delay Drop Out (TDDO) relay [EEIS / EIIS: El / 62)
(Manufacturer: General Electric/ Model: 12HGA17C52) associated with the 4 kV bus transfer circuit.
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. This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) due to the automatic actuation of the Reactor Protection System (RPS) and the AFW system as Identified in 10 CFR 50.73(a)(2)(iv)(B).
CORRECTNE ACTIONS PLANNED OR COMPLETED
- 1. Repaired grounded cable 1UYT0001E to 20-ET Turbine Trip Solenoid.
- 2. Revise maintenance and risk procedures for mitigation actions during ground detection activities and while using portable ground detection equipment.
- 3. Replaced the TDDO relay associated with the 1A 4 kv bus.
PREVIOUS SIMILAR EVENTS
There were no events from the last three years with either the same or similar cause to this event. Page 2
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