Fukushima worker on tsunami day
3 May 2012 Last updated at 04:59 BST
Few of the Japanese workers known as the Fukushima 50 have ever spoken publicly about the days after the tsunami-triggered nuclear crisis.
The BBC's Roland Buerk has been to meet one of them, Akihiro Harako, and asked him about the moment the buildings exploded.
He said the accident was beyond imagination and the explosion was so strong he jumped out of his chair.