"And when the hydrogen build-up blows the roof off the containment chamber?"
Chenobyl: Abandoned after the explosion
Public DomainChenobyl: Abandoned after the explosion - Credit: Jason Minshull

An historical instance of this happening is the incident at Chernobyl in Ukraine on 26th April 1986. This occurred when a team of inadequately trained safety workers tried to speed up safety tests by contravening a series of safety regulations. One of the reactors exploded thus prompting a number of other explosions. A plume of radioactive fallout shot into the atmosphere and dissipated over vast areas to the east and west. It is thought that over 60% of the fallout landed in Belarus, with nuclear rain falling as far away as Ireland. Fifty six people died as a direct result of the blast, but thousands more have died, and will continue to die, from cancer. Following the event 336, ooo people were forced to resettle outside the exclusion zone. This video clip provides an informative if partisan overview of the incident.