UE SU1.1 declared due to momentary loss of power from the qualified off-site source. Both
Emergency Diesel Generators started and loaded to supply power to both of the Emergency Buses.
'A' Service Water Pump did not start on Blackout sequencer. Sufficient Service Water flow is available from the other three operating pumps. All other systems operated as designed."
At 1304 EDT Robinson Unit 2 experienced a momentary grid voltage drop that lowered the 4kV bus voltage and initiated an automatic reactor trip. All rods inserted and decay heat is being removed by steam generator PORVs. In response to the reduced bus voltage, the Emergency Diesel Generators (EDGs) automatically started and loaded onto the emergency busses. At 1317 EDT, the licensee declared an Unusual Event (EAL SU1.1) due to the loss of offsite power. The licensee is currently investigating the cause of the grid voltage instability. The emergency busses will continue to be powered by the EDGs until the licensee has determined the cause for the voltage drop. All offsite power sources and all equipment is available. The licensee has notified the state government and Darlington County. The NRC Resident Inspector has been notified.
Notified DHS SWO, FEMA OPS Center, FEMA National Watch (email only), DHS NICC, Nuclear SSA (email only).
- * * UPDATE FROM ALEX CURLINGTON TO DANIEL MILLS AT 1658 EDT on 10/08/16 * * *
At 1303 EDT on 10/08/2016, a reactor trip occurred. The cause was under voltage to the plant 4kV buses due to an offsite grid disturbance. The cause of the disturbance is under investigation. Following the reactor trip, the Auxiliary Feedwater System actuated as expected on low steam generator level. At the time of the trip, the plant was in Mode 1. Currently, the Plant is in Mode 3. The current RCS Temperature is 550 degrees F (Average), and the Steam Generator Levels are in the range of 42 to 53% (normal range) with levels controlled by the Auxiliary Feedwater System. Decay heat removal is being controlled by the steam generator PORVs. 'A' Service Water Pump did not start on Blackout sequencer. Sufficient Service Water flow is available from the other three operating service water pumps 'B', 'C', and 'D'. All other systems operated as designed.
Due to the Automatic Actuation of the Reactor Protection System, this event is being reported as a 4-hour Non-Emergency per 10 CFR 50.72(b)(2)(iv)(B). Due to the valid actuation of Auxiliary Feedwater System, this event is also being reported as an 8-hour Non-Emergency per 10 CFR 50.72(b)(3)(iv)(A)(B)(6). At no time during this occurrence was the public or plant staff at risk as a result of this event.
The Resident Inspector has been notified.
- * * UPDATE FROM BOBBY STUCKEY TO DANIEL MILLS AT 2347 EDT on 10/08/16 * * *
At 2323 [EDT] Emergency Bus E-2 powered from off-site power."
The NRC Resident Inspector will be notified.
Notified R2DO (Bonser), IRD (Grant), NRR EO (Miller).
- * * UPDATE FROM BOBBY STUCKEY TO JOHN SHOEMAKER AT 0028 EDT ON 10/09/16 * * *
At 0011 [EDT] Robinson Nuclear Plant has terminated the Unusual Event.
Basis for the Unusual Event termination was restoration of power to Emergency Bus E-2 from off-site power.
The licensee has notified the NRC Resident Inspector.
Notified R2DO (Bonser), NRR EO (Miller), IRD (Grant), DHS SWO, FEMA OPS Center, FEMA National Watch (email only), DHS NICC, Nuclear SSA (email only).
- * * UPDATE FROM GEORGE CURTIS TO JOHN SHOEMAKER AT 0253 EDT ON 10/09/16 * * *
At approximately 2323 EDT on 10/08/2016, an auto-start of the Auxiliary Feedwater (AFW) Motor-Driven pumps occurred during the transfer of Emergency Bus power from the 'B' Emergency Diesel Generator (EDG) to offsite power. AFW system auto-start logic associated with Main Feed Pump (MFP) breakers being open is defeated when the EDG output breaker is closed. As such, when the EDG output breaker was opened during the power transfer while the MFP breakers were open, the auto-start logic was thereby met causing the AFW auto-start.
Due to the valid actuation of the AFW System, this event is being reported as an 8-hour Non-Emergency per 10 CFR 50.72(b)(3)(iv)(A). At no time did this occurrence pose undue risk to the health and safety of the public.
The NRC Senior Resident Inspector has been notified of this event.
H.B. Robinson Unit 2 was in Mode 3 during this event. Notified R2DO (Bonser).
