The feed water system for cooling water froze, and the plant had to be shutdown.
This is what happens when you don't plan your essential services to react to predictable extreme events.
That a nuclear plant can theoretically handle this sort of thing quite easily means nothing if you don't actually implement the systems to do so.
> STPNOC said in an event report filed with NRC that the unit tripped at 5:26 am
The feed water system has nothing to do with the turbines, and the plant shut down as a safety precaution.
I was perhaps a bit too hasty in my initial statement, clearly this reactor tripped because of the cold. I'm not an expert but given a nuclear power plant produces literally gigawatts of low grade waste heat it feels like that should have been possible to work around i.e. for example by bleeding cooling water back at the intake.
The nuclear plant's turbines were literally on the "roof" of the reactor complex completely in the open. Nuclear regulations only require the reactor itself to be enclosed and protected.
No shit the turbines froze over. They ignored reports advising them to fully enclose the plant for years.