I would argue that this is a near equivalence of nuclear war with Ukraine. A well-/mis-placed Russian artillery shell could cause a loss of reactor integrity and meltdown, no? EDIT: according to child comments, a meltdown is unlikely/impossible, but spread of radioactive particles due to a direct strike is possible.
If radiation escapes it would be a "dirty bomb" equivalent event, it will speed up sanctions and nations will urge Russia to allow experts to inspect the damage.
A meltdown/explosion is possible if they damage safety systems/shielding. Still won't be seen serious as a "nuke detonation" event, but countries that receive fallout will be pissed off.
If Russia continues causing more nuclear pollution that affects it neighbors, yes, it could mean war scalation.