In response to Chaoskiddo, you don't really need to worry about human error causing an explosion or spreading radiation over a city these days. Like BoC said, nuclear power is extremely safe. Each plant will generally have 3 independent shutdown systems that will come into effect the minute any abnormal or potentiall dangerous conditions are detected. For instance, in CANDU reactors the control rods are held up using electro-magnetic force. The minute the power is cut, there is nothing holding up the rods and they drop down and stop the reaction. This isn't to say that accidents can't happen, but the probability of a nuclear disaster is extremely low.

BoC is also spot on about the decommissioning. Right now in Canada, we have several reactors that are out of date and should really be shut down soon, but it's cheaper to keep them running than to take them out of service. Radioactive waste is probably the biggest problem facing the nuclear industry at the moment. Some of the waste produced has a relatively short half life, but other elements will stay radioactive for thousands of years. Still, compare this to extremely toxic elements that get casually thrown into landfills. They will never cease to be toxic, yet we don't give much thought to their disposal. Right now, Sweden is the best at disposing of their nuclear waste, sealing it in a giant underground vault beneath a lake, filled with concrete and neutron-blocking materials.

010577 is right about the waste being able to be recycled. We have the capability to process spent fuel and re-enrich it. Also, CANDU reactors require a lower enrichment of uranium than light water reactors, so we can actually use the spent fuel from the US in our reactors here.

In terms of cost, the only reason nuclear isn't the cheapest is because fossil fuels are so cheap. We've had access to a relatively cheap and abundant supply of fossil fuels, but that's starting to change. People are starting to realize that the supply is finite, and prices are starting to climb. If you want to check out a really great cost analysis which takes quite a few different factors into account, check out this website: http://www.uic.com.au/nip08.htm

The thing is, we can't phase out fossil fuel power plants completely. Nuclear reactors are quite expensive to turn on and off, therefore ideally we want to keep them running all the time. Power demand however, fluctuates quite a bit, peaking during the day and falling to a low at night. So it's best to use nuclear for the baseload and gas-fired plants to meet the daytime demand since these are easy and fast to fire up. The worry is that our supply of fossil fuel will be exhausted before we even have enough nuclear plants to meet the baseload requirement.