too early to jump to any conclusions. in case of radioactive leak the area affected will be million times larger than any refinery fire.

Most nuclear reactors will automatically scram if they lose power. The control rods are held up with electromagnets so they will drop if power is lost. Losing power isn't too dangerous. Loss of coolant is quite dangerous but there are backup systems that can flood the reactor with an alternative coolant source. For example a submarines can flood their reactors with seawater. You just don't want to do that except in an extreme emergency because it will destroy the reactor equipment.

Edit: It looks like the reactor had a coolant pump failure. The loops are intact. There is time to do something about this. The water has to boil off before anything really bad starts happening. At this point they would be concerned with saving the reactor from damage. Declaring a nuclear emergency is still a good idea. This is dangerous but not anywhere near three mile island. They know what's happening inside the reactor and can handle things accordingly.