Nuclear power can be a potential threat in multiple spheres :
1: Nuclear waste : The waste generated by nuclear reactors can remain radioactive for tens to hundred thousands years. There are not no long-term storage solution for nuclear waste. Nuclear waste are not likely to resist from natural disasters for instance with Fukushima.
2: Nuclear proliferation : States are more able to have nuclear power. The development of nuclear energy programs increases the likelihood of nuclear weapons' proliferation. This proliferation can increase the instabality of the international system.
3 : Nuclear Security : Nuclear power can be a target for terrorists. An attack could have terrible damage on population and the security of states.
However, nuclear power is one of the best source of energy and we are more and more people in the world. And it has a very low carbon print .
"I disapprove of what you say, but I will defend to the death your right to say it." (Hall, 1906, 199)