Well, inertially confined reactors (ie ones that uses hundreds of lasers to heat up the fuel and contain the plasma) are appearing to be more likely feasible, that's why I mention them. I believe the first one is coming online in the USA in a couple years.
It is true it is a Russian design for a fusion reactor, but the problem is most magnetically confined reactors are based on the old Tokamak design, which has not worked yet. I'd say it has something to do with lacking sufficient free neutrons, but I'm not a nuclear physicist so I don't know if that would help or not.
Well I may be wrong about the coolant system, but it would make sense to have an underground containment vessel, in case the reactor is damaged or the reaction is unstable. It would make sense to me to have the reactor suspended over some kind of pit and drop it inside and seal off the pit in case the reactor was going critical to either minimize damage to surrounding areas or have a failsafe in place to cool off / deactivate the reactor harmlessly once inside the pit. Coolant is there to keep it running optimally in most situations; a containment vessel is there to contain a nuclear explosion or defuse the reactor when it is going out of control. So, make sense to have an underground containment vessel.
Stellarator reactors may be better, or may suffer from the same problems as other magnetic confinement options. Hard to say.
I'd say OP1 wasn't realistic actually. They tried so hard to be realistic that it became realistically unrealistic. If they wanted it to be super realistic it wouldn't have been a game as extreme realism doesn't work in a game environment. Some amount of realism works, but there is a need to have some abstraction and without it the game feels dull and boring. Well, that is, my opinion at least.