Uranium nitride refers to a family of several ceramic compounds: uranium mononitride (UN), uranium sesquinitride (U₂N₃), which exists in either an alpha or beta phase, and uranium dinitride (UN₂).

Uranium mononitride was used as driver fuel for two core loads of the sodium cooled BR-10 reactor in Russia. It has also been proposed as nuclear fuel

Nuclear fuel

Nuclear fuel is a material that can be 'consumed' by fission or fusion to derive nuclear energy. Nuclear fuels are the most dense sources of energy available...

 in some fast neutron nuclear test reactor

Nuclear reactor

A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

s. The property which makes uranium mononitride highly attractive as a nuclear fuel is the combination of a high melting temperature with high thermal conductivity. The thermal conductivity is on the order of 4-8 times higher than that of uranium dioxide, the most commonly used nuclear fuel, at typical operating temperatures. Increased thermal conductivity results in lower thermal gradients between inner and outer sections of the fuel, potentially allowing for higher operating temperatures and reducing macroscopic restructuring of the fuel, which limits fuel lifetime.

Uranium nitride can be synthesized by the reaction of nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 with uranium

Uranium

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 at 700 K. Uranium nitride may be formed as a minor product of uranium combustion in air; however, the more thermodynamically stable uranium dioxide will be the major product.

According to an article in "Nuclear Engineering International", uranium nitride (enriched to less than 20% U-235) is the fuel chosen by Hyperion Power Generation

Hyperion Power Generation

Hyperion Power Generation, Inc. is a privately held corporation formed to construct and sell several designs of relatively small nuclear reactors, which they claim will be modular, inexpensive, inherently safe, and proliferation-resistant...

to fuel their recently revised Hyperion Power Module. This article, however, incorrectly states that uranium sesquinitride will be used, rather than uranium mononitride. The correct information is available at http://www.nrc.gov/reactors/advanced/hyperion.html