Here's a link to a lot of information from a "worst case" scenario prepared by the UK government in the early stages of the Fukushima-1 disaster: click here for report!

The inventory of high level nuclear waste and fuel at this plant is "nearly double" what was at the Chernobyl nuclear complex but the British thought the environmental impact would be less if there were an explosion because it wasn't encased in graphite, i.e., the resulting plume would not rise as high in the air.

Charley Noble