For many years, my opinion of nuclear power has been one of an uneasy truce: I've not been 100% comfortable with it, but accepted it because of the potential to generate a lot of power relatively pollution-free.
In the wake of the accident at the Fukushima power plant, I'm rediscovering some things I kind of knew before but hadn't fully appreciated:
Historically speaking, far more people have been killed by fossil fuel power than nuclear power. This is a fact.
But that's not because nuclear power is inherently safer. On the contrary: nuclear power has a good safety record (so far) because it is so extremely dangerous that we entomb reactors with insanely large containment structures to keep the stuff away from us even in an unthinkable disaster. Were we to build similar containment and waste-handling systems for coal-fired power plants, pollution and global warming would be non-issues.
We don't do that with coal and oil because we don't have to.
And if a containment structure is ever catastrophically breached (an event which hasn't happened yet--the Chernobyl reactor had no containment), it would likely render hundreds of square miles uninhabitable for centuries. Nothing else made by humans has that capacity.
Even after decades of nuclear power, we still haven't figured out what to do with the spent fuel. Fukushima shows that in an accident the spent fuel can be almost as dangerous as the reactor itself, in its capacity to contaminate the surroundings and prevent emergency workers from fixing problems.
Here in the U.S., spent nuclear fuel is basically stockpiled at the power plant waiting for the (hypothetical) day when there's some way to recycle or dispose of it. At the Prairie Island plant here in Minnesota, they've actually run out of storage space and have had to build new storage casks. It's safe to assume that these spent fuel casks are considerably more vulnerable than the primary containment around the reactor.
The nuclear accidents at Chernobyl and Three Mile Island happened because of internal problems, not because of a natural disaster. Fukushima, on the other hand, was caused by a combination of a magnitude-9 earthquake and a massive tsunami--an event the power plant was not designed to survive.
Nuclear reactors are engineered to withstand the most catastrophic natural disaster expected at their site. What that means in practice is that a natural disaster big enough to damage a nuclear power plant will be bigger than anything anyone expects. Normally simple things like transportation may be difficult or nearly impossible, local emergency services may be wiped out, and it could take days to get even the most basic resources to fix the problem.
If bringing a nuclear power plant under control requires something (supplies, people, expertise) which doesn't exist at the site itself, you might not be able to get it at all.
One argument by nuclear advocates post-Fukushima has been that the Fukushima reactor and containment was an older design with known deficiencies. New plants, they argue, would never be as vulnerable.
Unfortunately, older reactors continue to be used, even decades beyond their original design lifetime. Given the cost of decommissioning an old reactor and building a new one, power plant owners have an enormous incentive to keep the old reactors running as long as possible.
It's hard to know if the margin of safety in older nuclear plants has eroded (it may take another disaster to know for sure), but it is clear that they are not being replaced by newer designs nearly as quickly as the original designers had intended.