Accidents can and do happen. Even in the best managed plants that were planned and built with the highest levels of safety in mind, there is always a chance of a nuclear meltdown. With Chernobyl, the meltdown was caused by a design flaw and a lack of safety culture. While the type of nuclear reactors used at the Chernobyl facility have either been decommissioned or have addressed the design flaw that caused the Chernobyl disaster, there are still 10 in operation. The scientific community widely considers these reactors to be more unstable and less safe than western style reactors. At Fukushima, the meltdown was caused by an earthquake and tsunami. In the Fukushima accident, all safety measured kicked in--the plant automatically shut down when the earthquake was detected. However, after the shutdown, the generators which were circulating coolant through the reactor to keep it stable were damaged by the tsunami. The generators stopped pumping coolant through the reactor which resulted in the nuclear meltdown. The simple fact of the matter is, nuclear reactors are highly complex and have a lot of moving parts. All it takes is one missed cue or faulty part to cause an accident, and when dealing with nuclear reactions, an accident can be catastrophic. There is no way to completely eliminate the chance of nuclear meltdown. Nuclear energy is not safe.
The Chernobyl accident was largely a result of a lack of safety culture in the Soviet Union. Since the disaster, there has been lots of progress made in regard to safety measures, the design of nuclear plants, and the cooperation between governments to ensure that a disaster like Chernobyl does not occur again.
[P1] Nuclear reactors are complex. [P2] The more complex something is, the more likely it is to malfunction. [P3] The low chance that a reactor melts down is enough to make them unsafe.
Rejecting the premises
[Rejecting P2] There are highly-qualified professionals who ensure that these plants function properly.