Nuclear energy is hugely susceptible to black swan events, with very serious environmental and monetary consequences. Even the best, safest run facility, in an instance of sabotage, terrorism, conflict, or simple unexpected event (seismic, extreme weather), can turn into a maelstrom of troubles that will endure for thousands of years.

Further the nuclear industry is one with a very poor track record of promises versus delivery. The cheap power, for instance, tends to turn into expensive power when plants need to be refurbished at mind-boggling costs (such as here in Ontario where we've gone from the cheapest power in North America, courtesy of huge hydroelectric benefits, to one of the most expensive because of our nuclear legacy). And the waste issue remains a significant issue.

Nuclear was a great alternative to fossil fuels. It is a very poor alternative to alternatives (wind, solar, geothermal, hydroelectric, etc), and simply increasing energy efficiency.