Fast thorium safe (no radiation damage) breeder:
http://two66.com/reactorplanne…7k1g1rlpboh41fw78lbfssavy
Approx 2.5 minutes per 4 uranium cells.
Alternatively, with radiation damage:
http://two66.com/reactorplanne…wvqt29uqba1zwr0m8yr7drbz3
Cheaper and slightly faster.