WHO | Chernobyl: the true scale of the accident

In the wake of the Japanese nuclear plant failures, this is a good source for perspective: WHO | Chernobyl: the true scale of the accident
The thing to remember is, Chernobyl was horribly mismanaged and was pretty close to the reasonable worst possible case. (An unreasonable worst possible case would be dropping a nuclear bomb on the pile once the containment vessel had ruptured.) They don't expect anything nearly as bad in Japan.