That's because you're mind is clouded by the effects of a mental fallacy (the availability heuristic to be precise) http://en.wikipedia.org/wiki/Availability_heuristic
No matter how you compute statistics, a nuclear meltdown is a big downside risk. It can happen, and if it happens it's extremely destructive. It's an event with a small chance of occurence but with great consequences.
That's qualitatively different from something like traffic accidents. The chances of those happening are much higher, but if they happen, they affect at most a few people, They won't turn your city into a 'wildlife reserve' for years to come.
Even though the total amount of people that die of traffic accidents is higher, to me it's less scary. The risks are more manageable: you have some degree of control over it (drive safely) and the consequences are visible.