Of the three most notable meltdowns(Chernobyl, TMI, Fukushima), two were completely preventable, one is a testament to how safe nuclear power really is
Up until cherobyl and even a few cases after, most russian reactors operated with a neutron moderator that actually increases reactivity with increase in temperature. so the hotter it gets, the hotter it wants to make it, so it gets hotter, and so on and so forth until there is operator action to curtail the reactions and bring reactivity down to zero and retain stable operations. when chernobyl melted down, they were testing the reactor's response to a loss of power to the circulating pumps. so now you've greatly reduced the amount of cooling in a system that exponentially increases temperature. good luck.
every nuclear reactor in the non third world operates using a neutron moderator that reduces reactivity as the temperature rises, thus governing itself. the entire system is also designed to shut itself down if everything is not perfect. TMI happened because pressure was decreasing and nobody was doing anything about it. they had indications, they could have prevented it, but nobody wanted to operate anything. pressure decreased below the saturation point of the cooling water flashing it to steam, which doesn't remove heat within the core very well, so it melted down.
in fukushima, the plant was responding to an earthquake, a tsunami, and a power outage all at the same time. the "meltdown" that occured was the final result of a lack of cooling flow within an already shutdown core. the actual release radiation was far less than advertised and most of it went out to sea and fell into the ocean, the biggest "victims" of the "meltdown" were the navy ships we sent in to help them through the process and lab technicians that went over every inch of every ship that drove through the plume and found next to nothing above background radiation levels.
There is a huge difference between a nuclear reactor and a nuclear bomb. there are two types of neutrons, fast neutrons, which are moving quickly and thermal neutrons which are moving slowly. a nuclear reactor runs on thermal neutrons, which are born from nuclear reactions and need to slow down, thus limiting the number of reactions that can occur at any given time. a nuclear bomb contains a fuel that is made to run on the fast neutrons, thus not limiting the number of reactions that can occur in a given time frame allowing the reactions to occur very quickly.
you can not detonate a power plant reactor, as nuclear operators, we love watching movies such as "the world is not enough" and laughing maniacally at everything that is not even remotely possible.
reactor plants are designed to contain the radiation and are placed a distance far enough away from anyone and anything to ensure the dose of radiation given to the people is low enough to not cause any problems. the "explosion" that occurs in reactors is a steam explosion when pressure gets too high and a part fails. if you want to limit your exposure to radiation just walk away. in almost every case, doubling your distance from the radiation, reduces your dose by over 5 times.
spreading out the radiation would not be good for anybody. you want to contain it and shield it.