http://www.talonfiremage.pwp.blueyonder.co.uk/reactorplanner…zw9hb4is9r5xpfk
All externally cooled. No internal components needed. Put in five lava buckets to get the temp to 10,000~ and you are ready to go.
You can have a temperature sensor trigger a piston to let in extra water to add cooling just in case something happens.
This is untested, and purely theoretical.