I don't think so. otherwise CCJ wouldn't have been selling it for $20/lb on long term contract last yr. this is ore; this isn't plutonium. storage is probably very similar to iron ore. (in other words, you make a big pile and you put a cover on it with a lock)
If there was a $1 / day carry cost on the contract (which is this case it's about 1%), then it'd be too easy to just short contracts and make a killing.