The energy of the reaction is mostly carried away as high-energy neutrons. So, the way to get energy back is to "capture" those neutrons. Since neutrons are not electrically charged, you can't use them to directly create electricity, so all you're left with is using them for heat.
Unfortunately, since they are electrically neutral, they're also relatively hard to catch. You need a dense material where they will have a good chance to hit some nucleus. The proposed designs are typically some kind of liquid metal blanket being circulated around the reactor and onto a place where it can boil water to produce steam to spin a turbine. Lithium is the metal most proposed for this, since it also has the advantage that it can produce tritium when bombarded with neutrons (tritium being the super rare half of the fuel that goes into the reaction).