If a nuclear power plant suddenly gets cut off from the grid like Khmelnytsky NPP and Rovenskaya NPP do the reactors have to SCRAM? All that power have nowhere to go otherwise isn't it?
Once SCRAMed how long would it take to bring the reactor back online?
A nuclear reactor doesn't turn the reaction directly into electricity
All that reaction does is generate heat, which in turn is used to boil coolant which turns to steam, to turn a turbine. The turbine is what generates electricity not the reactor itself.
The reactor can essentially run at full power and not generate any electricity at all so long as the steam is condensed and cooled back into liquid coolant form to continue cooling the reactor.
They can run the plant in a mode called "islanding" where the plant can generate the electricity it needs to keep the cooling systems operation while having no connection to any outside grid.
These ones that are scrammed all that means is all control rods are inserted to smother the nuclear reaction
Turn around time is probably a couple days tops
The most important thing is keeping the nuclear fuel cool, as long as that's done there is nothing to worry about. If they are fully shut down and disconnected as claimed, all they have to do is ensure a constant supply of diesel fuel to all of these facilities (for the backup generators)to ensure they don't melt down. Should be plenty of diesel available in the western BFF countries for this.
The concept of nuclear power plants are incredibly simple marvels of engineering, it's essentially an extremely powerful, over engineered kettle, with a few lines you do not cross