TVA prepared for earthquakes at their nuclear power plants
Last week's magnitude 4.4 earthquake in Decatur, near Watts Bar Nuclear Power Plant, prompted questions about the safety of nuclear plants during and after earthquakes.
"When the plant was originally licensed and constructed, we looked at the most severe events that happened in this geological area over a multi-year period into the centuries," Chris Reneau, Site Engineering Director at Sequoyah Nuclear Power Plant, said.
Using this analysis, the area's nuclear power plants were built to withstand earthquakes, tornadoes and large-scale severe flooding. Additionally, TVA routinely follows maintenance protocols to check equipment functionality.
"From an operations standpoint, this is just one of the many events that they are trained to respond to, and we have scripted procedures in what we call enunciated responses and abnormal operating procedures," Kevin Michael, Operations Superintendent at the Sequoyah Plant, explained
Their scripted responses are to ensure all proper steps are followed, and information is repeated by employees for confirmation. Operators train in simulations every five weeks for 240 hours a year.
TVA ran two simulations today at their Sequoyah Training Center to demonstrate the control room alarms and how employees respond to an earthquake similar to last week's size and a second, potentially larger earthquake.
Last week's earthquake was well below their Design Base earthquake threshold, which is based on the building's construction and ground movement, not typical earthquake magnitude number. Sequoyah had no ground movement last week, and Watts Bar only had one warning, indicating seismological activity.
This warning light was demonstrated in TVA’s first simulation, along with the employee scripted response of equipment to check.
The second simulation was for an earthquake 10 times greater than the one which occurred in Decatur. Multiple alarms sounded and lights flashed indicating more instruments registered the ground movement, including the turbine vibration alarm.
These warnings "prompted operators to take response by their station procedures, to walk the plant down, to validate the alarms that were in and ultimately, to ensure stable plant operations," Michael said.
This simulated earthquake was still within the Design Base Event, which may or may not require a reactor unit shutdown.
"Beyond Design Base Events and that's when we have multiple flexible coping strategies to be able to handle those events to preclude an event that Japan suffered in the 2011 time frame," Reneau stated.
If a Beyond Design Base Event ever occurs, TVA assures that units can be shut down immediately in one second.
In the control room, three people are assigned to each reactor unit, and there is a shift manager. Plus, there are eight assistant unit operators that take necessary action in the field checking on the facilities after events.
Through training and plant processes, TVA rigorously follows their procedures to keep the public safe from earthquakes and other natural events.