U.S. Nuclear Regulatory Commission
10/08/2021 - 10/12/2021
|Unit||SCRAM Code||RX Crit||Initial PWR||Initial RX Mode||Current PWR||Current RX Mode|
|2||A/R||Y||95||Power Operation||0||Hot Standby|
"At 1321 EDT on October 11, 2021, Susquehanna Steam Electric Station Unit 2 reactor automatically scrammed due to a trip of the Main Turbine.
"Unit 2 reactor was being operated at approximately 95 percent RTP [rated thermal power] with no evolutions in progress. The Control Room received indication of a Main Turbine trip with both divisions of RPS [Reactor Protection System] actuated and all control rods inserted. Turbine bypass valves opened automatically to control reactor pressure and subsequently failed open causing the reactor to depressurize. When reactor pressure reached approximately 560 psig, the operations crew manually closed the Main Steam Isolation Valves (MISVs) to stop the depressurization. Reactor water level lowered to -31 inches causing Level 3 (+13 inches) isolations. No [automatic] ECCS [Emergency Core Cooling System] actuations occurred. HPCI [High Pressure Coolant Injection] and RCIC [Reactor Core Isolation Cooling] were manually initiated to control reactor water level. The Operations crew subsequently maintained reactor water level at the normal operating band using RCIC and reactor pressure was controlled with HPCI in pressure control mode and main steam line drains. The Reactor Recirculation Pumps tripped as designed on EOC-RPT [end of cycle recirculation pump trip].
"The reactor is currently stable in Mode 3. An investigation into the cause of the turbine trip is underway.
"The NRC Resident Inspector was notified. A voluntary notification to PEMA will be made.
"This event requires a 4 hour ENS notification in accordance with 10 CFR 50.72(b)(2)(iv)(A), 10 CFR 50.72(b)(2)(iv)(B) and an 8 hour ENS notification in accordance with 10 CFR 50.72(b)(3)(iv)(A)."