On 18/02/2013 00:12, Windmill wrote:
Maybe my question should have been not to ask what I131 decays to, but
rather what decays to I131.

Not a lot as far as I can tell. It's a product of the fission reaction,
and once that has been stopped (within minutes in Fukushima) Iodine
production stops too.

I131 is one of the reasons the reactors are hard to stop quickly;
there's a lot of energy released in the decay process, so the reactor
still makes heat even after fission has been stopped.

Andy