Heat released by a spent fuel assembly
A uranium oxide (UOX) fuel assembly weighs approximately 500 kg. Five years after being unloaded from the reactor, it emits heat equivalent to around a dozen 100 watt light bulbs. This heat release steadily tails off, falling to 85 watts after 300 years. Spent fuel assemblies must be cooled prior to disposal, either in a pool or in dry silos.
CNE (2004 assessment report)