Put yourself in the chief operator's perspective: An armed force has indiscriminately killed the plant's security that have guns far more powerful than anything

Put yourself in the chief operator's perspective: An armed force has indiscriminately killed the plant's security that have guns far more powerful than anything allowed near the control room. If the reactor is in a state that would require the control rods to be reinserted to prevent melt down along with activating any authorization requirement to allow reinsertion, then when the orders come with guns pointed at your head and if you are allowed to talk you demand the occupiers leave and be permitted to re-insert the control rods to bring the reactor under control otherwise if they immediately kill you, then its their problem. Why demand they leave on first contact? A person pointing a gun or in this case shelling you with artillery is untrustable. If they initially obey, then it not only has bought you time, but an understanding that the attacker cares about the plant is established, which the operator has been entrusted with having as a value. It becomes the highest priority as it is the largest nuclear power plant in Europe and has been the largest Ukrainian power plant. Strategically, it makes sense to seize an asset while keeping it in tact, but bombs are not known for precision.