05000321/LER-2021-001, Edwin L Hatch Nuclear Plant, Unit 1 Re Automatic Reactor Scram on Low Reactor Water Level Due to Loss of Reactor Feed Pumps
| ML21274A418 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 10/01/2021 |
| From: | Dean S Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-21-0828 LER 2021-001-00 | |
| Download: ML21274A418 (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 |
| 3212021001R00 - NRC Website | |
text
A Southern Nuclear Sonny Doan Hatch NuCltJl'lr Plant Vie@ Pro ldont - Plant H teh 11028 Holch Parkway North Boxley, GA 31513 October 1, 2021 ATTN: Documrrt Control Desk U.~. Nucleir Regu!~tory Commi~sion Wa$hlngton, DC 20555~0001 Edwin L Hateh Nuclear Pl~nt ~ Unlt 1 Licen~~ ~vent Report 2021a001~00 012 53'1 5859 lal
!'112 366 2077 fm:
Autom~tie Reactor Se.ram on Low Reactor Water Leve.I du~ to Loss o'f.Reactor Feed Pum ~s In accordance with th requiremenw of 10 CrR 50.73(~)(2)(lv)(A), Southern N!.!clear Operating Comp~ny hereby ~ubmits th enclosd Licen$e@ Event Report.
This letter oont~lns no NRC commitmerr~. If you have ~ny question~, plea$ conffict th Plant Hatch Llcnsing Manager, Jimmy Collins, at 912.453.2342.
Respectfully submitt~d, SD/CJC cc:
NRC Regiontill Administrgtor, Rgion II NRR Project Man~ger = Plant Hatch NRC Snior Re~ident lnipctm = Pl@lflt H~teh RTYPE: CHA02.004
Edwin I. Hatch Nuclear Plant - Unit 1 Licensee Event Report 2021-001-00 Automatic Reactor Scram on Low Reactor Water Level due to Loss of Reactor Feed Pumps Enclosure LER 2021-001-00
Abstract
On 08/03/2021 at 1026 EDT, Unit 1 experienced an automatic reactor SCRAM and containment isolation due to low reactor water level. A spurious trip of a Turbine Building 600V breaker caused a loss of control power and immediate trip of both 1A and 1 B reactor feed pumps. Due to loss of reactor feedwater, the reactor water level lowered to the setpoints for the following automatic actuations: reactor SCRAM, High Pressure Coolant Injection (HPCI) start, Reactor Core Isolation Cooling (RCIC) start, and both primary and secondary containment isolation. All safety-related actuations occurred as designed. Reactor operators responded to stabilize the plant and control reactor water level. Unit 2 was not affected. The initial notification to the NRG was documented in Event Notification 55394.
Corrective action was completed to replace the failed breaker with a more reliable breaker.
This event is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A) due to actuations of systems listed in 10 CFR 50.73(a)(2)(iv)(B).
EVENT DESCRIPTION
Prior to the event on 08/03/2021, Unit 1 was operating at 100% power. There were no inoperable structures, systems, or components that contributed to the event.
At approximately 1025 EDT, the 1 B Turbine Building 600V breaker 1 R23S002FR6T tripped, due to a spurious trip of its Digitrip 610 trip unit. 1R23S002FR6T is the normal supply breaker to 1A 120/208V Station Service Switchgear 1R23S021.
The loss of power to 1 R23S021 resulted in both 1A and 1 B reactor feed pump turbines losing power to their Mark Vie control panels, resulting in a dual reactor feed pump trips. The loss of both reactor feed pumps resulted in a loss of feedwater and lowering of reactor water level.
At 1026 EDT, automatic reactor SCRAM and primary containment isolation occurred at the Reactor Pressure Vessel (RPV) Low Water Level setpoint. All control rods fully inserted. After the SCRAM, the actuation setpoint was reached for automatic start of the High Pressure Coolant Injection (HPCI) [EIIS BJ] and Reactor Core Isolation Cooling (RCIC) [EIIS BN] systems and for secondary containment isolation. All safety-related actuations occurred as designed.
Reactor operators responded to stabilize the plant and control reactor water level within band.
EVENT CAUSE ANALYSIS
The event was determined to be caused by a spurious trip of the Digitrip 610 trip unit on the 1 B Turbine Building 600V breaker 1 R23S002FR6T.
REPORTABILITY AND SAFETY ASSESSMENT
This event is reportable pursuant to 10 CFR 50. 73(a)(2)(iv)(A) due to the following system actuations:
Reactor Protection System (RPS), general containment isolation signals affecting containment isolation valves in more than one system, or Emergency Core Cooling System (ECCS) for Boiling Water Reactors (BWRs) including HPCI and RCIC.
There were no safety consequences as a result of this event. There were no safety-related systems that failed during this event. The operating crew responded correctly to the event. The applicable abnormal/emergency operating procedures were entered. The event was within the analysis of the Updated Final Safety Analysis Report (UFSAR) Chapter 15.
No radiological release occurred due to this event.
CORRECTIVE ACTIONS
The corrective action replaced the Digitrip 610 trip unit on the 1B Turbine Building 600V breaker 1R23S002FR6Twith a General Electric Microversa Trip Plus (MVT +) trip unit, which is proven to be more reliable.
PREVIOUS SIMILAR EVENTS
Plant Hatch had two previous events caused by spurious trips of Digitrip 610 trip units. These events occurred in 2008 and 2014. In both cases, power was lost to 1 F Control Building 600V bus 1 R24S030. Loss of power to 1 R24S030 did not result in a total loss of a significant plant system, a transient, or a down power of the unit. Page 2
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