05000277/LER-2024-001, Automatic Reactor Scram Due to an Invalid Generator Lockout

Automatic Reactor Scram Due to an Invalid Generator Lockout

ML24081A121
Person / Time
Site:	Peach Bottom
Issue date:	03/21/2024
From:	Constellation Energy Generation
To:	Office of Nuclear Reactor Regulation
Shared Package
ML24081A118	List: 05000277/LER-2024-001, Automatic Reactor Scram Due to an Invalid Generator Lockout
References
CCN: 24-14, ENS 56936 LER 2024-001-00
Download: ML24081A121 (1)

LER-2024-001, Automatic Reactor Scram Due to an Invalid Generator Lockout

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
2772024001R00 - NRC Website

Abstract

On 01/29/2024 at 1202 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.57361e-4 months <br />, Unit 2 experienced a Generator lockout, Turbine trip and automatic Reactor Scram. All control rods inserted, and all safety systems responded as designed. Reactor level was initially maintained by Feedwater and pressure controlled with bypass valves. During the scram response, condenser vacuum degraded due to the loss of Turbine steam seals, resulting in level and pressure control being transferred to Reactor Core Isolation Cooling (RCIC) and High Pressure Coolant Injection (HPCI), respectively.

The cause of the Generator lockout is under investigation, with the suspected cause being a spurious trip of the Audio Tone system. The system has been removed from service with a redundant system providing the protective function. The Audio Tone system is scheduled for replacement in the 2024 refueling outage.

This event is reportable under 10CFR50.73(a)(2)(iv)(A) due to manual or automatic actuation of systems listed in 10CFR50.73(a)(2)(iv)(B) including the Reactor Protection System, containment isolation signals, actuation of an emergency core cooling system and Reactor Core Isolation Cooling. An ENS notification was made within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of the event and was updated within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, reference ENS 56936.

(See Page 2 for required number of digits/characters for each block)

(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/) Page 3 of 3 cooling system and RCIC. An ENS notification was made within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of the event and was updated within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, reference ENS 56936.

Safety Consequences

The reactor Scram occurred as designed and resulted in no safety consequences. All safety systems responded as expected. As described above, the temporary degradation in condenser vacuum resulted in use of the RCIC system to control level for a portion of the response, but this did not challenge the ability to safely shutdown and cool down the unit.

Corrective Actions

Immediate corrective actions were taken to remove the affected Audio Tone system (TTR-1) from service and utilize the fully redundant TTR-2 system. The TTR-1 Audio Tone drawer has been replaced and a new set of cables has been identified and tested. After the completion of additional testing, this system will be maintained in a standby condition as a spare. The Audio Tone system is scheduled for a complete replacement in the upcoming 2024 refueling outage.

The corrective action to address the condenser vacuum degradation is to revise the procedure which sets the sealing steam pressure control valve to ensure it will receive the appropriate demand signal when needed.

Previous Similar Events

Peach Bottom has not experienced a Scram due to a Generator lockout in at least 10 years. The station experienced a trip of the Audio Tone system for an offsite source due to cable degradation in 2001 (Ref. EN 38241).