QMC (University of
:London) used to have a small nuclear reactor in Stratford E15. That's right where the London 2012 Olympic Park has been built. We had a visit there in 1981. They used to heat up a bit of water from the local stream and pour warm water back (kept the frogs happy). We asked "What happens if it melts down?" and the nuclear physicist who was showing us round said, "It's OK, not many folks live nearby.".
The reactor closed in 1982 and was de-commissioned shortly after that.So Usain Bolt won't be nuclear powered when he runs the 100m.