NILFiR stands for Neutron Induced Lithium FIssion Reaction
This is the reaction:
Li-7 + N => Li-8
Li-8 => Be-8 + 16 MeV
Be-8 => 2 He-4 + 90 KeV.
The total energy gain is ~16.1 MeV. The energy density is about 2 MeV/AMU (193 trillion joules/ Kg) more than twice Uranium.
Now all of this so far is great, but you would need an expensive and power hungry external neutron source because this reaction doesn't produce any neutrons.
This is how I would alleviate this:
Deuterium contains a proton and a neutron. The binding energy per nucleon is about 1.25 MeV. That meant that to split it, and create a proton and a neutron, you need 2.5 MeV (actually 2.45, but close enough). The fission products (2 alpha particles) have 8 MeV each, so a collision with deuterium will be enough to split it. If bound up in LiD (Lithium Deuteride), I would think that about 3 neutrons per fission would be generated, although I have no real idea. Another possible way to generate neutrons is Beryllium. An alloy of lithium and beryllium would stay solid at higher temperatures and need less energy per neutron.
The cross section for the reaction is small, .05 Barns, but the high neutron yield per mass, and the fact that the lithium atom is small to begin with, should keep the critical mass small. It will also help that D is a neutron moderator. Another positive is that the most radioactive thing this reaction can POSSIBLY create is tritium, which isn't that bad.
Li-8 decay: http://nucleardata.nuclear.lu.se/Nuc....asp?iZA=30008 Be-8 decay: http://nucleardata.nuclear.lu.se/Nuc....asp?iZA=40008 Reaction Cross-Section: http://www.ncnr.nist.gov/resources/n...ements/li.html