Earlier quoted context omitted.
A few artillery shells probably won't breach the containment. Missile shielding is part of the plant design (I don't know what level of shielding; US plants are designed to withstand a strike by an airliner). Not saying that the attack is thus acceptable, just saying that it will take a concerted effort to breach the containment.
How old's the plant? To what design is it built? I feel like the CFIT design basis is already a little optimistic, but we also don't know that that was the design basis in this case.
For what it's worth, the russian convoy is firing on the administrative building, not the power units themselves, but I don't know specifically what is in said admin bldg or what the ramifications for operation/shutdown of the power units/cooling systems works if the admin building burns down and/or gets shot up.