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NILFiR stands for Neutron Induced Lithium Fission Reaction. So far as I know, I am the first to think of the potential that this reaction has in power generation (though I will retract this claim if anyone finds a citation for something earlier than March 3, 2008 on this topic). The reaction itself releases 16 MeV. Though not yet tested, this reaction looks very promising for power generation the world over, not least because it cannot possibly be used in a nuclear bomb. The reaction would most likely be in the liquid phase, with a mixture of pure elemental Lithium and Beryllium in a carefully controlled ratio. The reactor would involve fairly similar technology to a Molten Salt reactor.

The Reaction

Li-7+n->Li-8->Be-8->2 He-4

The reaction is caused by Lithium-7 absorbing a Neutron. This creates Lithium-8, which has a half life of about 838 milliseconds. This is one out of 2 reasons why this reaction could not be used in a nuclear bomb: 838 seconds after a uranium nuclear bomb goes off, it has already long exploded. This would mean that a nuclear bomb based on NILFiR would "fizzle" and prevent any serious detonation. The other reason is that the Beryllium involved in neutron production would take a significant amount of time, on the scales of a nuclear explosion, to generate neutrons.

The energy is released primarily in the reaction Li-8->Be-8. This is a beta decay reaction. It releases the 16 MeV in 2 forms: 13 MeV of it in a very high energy electron, and 3 MeV of it in a neutrino. The neutrino will in essentially all cases be lost to the rest of the universe without interacting with anything else. That leaves 13 MeV (technically, 12.9645 MeV. Close enough.). 90 further KeV are released in the reaction Be-8->2 He-4. However, in comparison to the amount of energy released through other means, this is very much negligible. It is enough energy to make the 13 MeV figure accurate, though.


In terms of radioactive isotopes, none are inherently created in this reaction. All light elements are involved, and any radioisotopes released in this reaction will decay to negligible levels literally within one minute of being in the reactor. The reactor vessel, however, is another matter. A neutron flux will inevitably lead to some level of radioactivity in the reactor vessel. However, this will be radiation of a more low level and would not pose a very serious risk to public health, provided that it is disposed of carefully. There is one instance in which the production of radioisotopes becomes possible, but I will expand upon that later.

It is possible that Beryllium-10 could be produced as a result of Beryllium-9 in the reactor absorbing a neutron. This will happen in a fairly small fraction of cases. At the optimal Be:Li ratio for neutron production of 1.68, 22% of neutrons will be absorbed by Beryllium instead of Lithium. It is also possible that fast neutrons, which are an intermediate in neutron production, could be absorbed by the Lithium nucleus, which would cause the release of a tritium nucleus.

Neither of these two isotopes are extremely dangerous. They both decay via beta decay. Beryllium-10 has a half life of 1.5 million years, and Tritium 12 years. A relatively small amount of shielding will keep both well contained.

Neutron Production

Next up is the reaction for neutron production. Pure lithium, when bombarded with low energy neutron, will generate 1 high-energy electron and 2 moderate-energy Helium-4 nuclei. Pure Lithium will not generate neutrons to make this a self-sustaining chain reaction unless some mechanism is added to create the neutrons. However (and this is important, and it seems, fairly often confused), by the addition of Beryllium to the Lithium, the high energy particles can cause the Beryllium nucleus to split. The reaction is:

Be-9-> 2He-4+n

This reaction absorbs, by my calculations, 1.67 MeV. I got this by subtracting the mass of a Beryllium atom from the mass of 2 Helium-4 atoms and a neutron. This is in approximate agreement with the number given on Wikipedia of 1.6 MeV per reaction. Since my number is higher and more precise, I am inclined to go with it. instead. This energy is obtained by a collision with a fission fragment with a high energy. These collisions can happen until the fission fragments have energies below 1.67 MeV, at which point neutron production from that particular reaction stops. By my calculations, when the Be:Li ratio (by number of atoms, not by mass) is 2:1, 3.64 neutrons will be produced per fission. However, a certain


  • Li-8 decay: [1]
  • Be-8 decay: [2]
  • Lithium Neutron Cross Section: [3]
  • Beryllium Neutron Cross Section: [4]