[ RadSafe ] Spent fuel and decay

[Brennan, Mike (DOH)]

Does anybody know of any calculations as to how long it takes spent fuel
to decay to the activity level it had before going into the reactor?  I
realize it is highly dependant on factors such as level of enrichment,
amount of burn-up, activation of cladding, etc, and breeding of Pu.
Still I would be interested in knowing what the numbers look like.