Modeling of Phase Separation in Uranium Mononitride

Abstract

Semiempirical modeling of uranium mononitride decomposition was carried out using the laws of the chemical kinetics of heterogeneous reactions. All calculations based on results received from thermal stability tests of UN at high temperatures. Kinetic curves of UN decomposition products correspond to the self-accelerating decomposition, which follows the induction period. The experimental data of uranium nitride mass loss in the investigated range of parameters are well described obtained results. The modeling can be used to estimate the phase composition of uranium mononitride during high-temperature tests in an atmosphere that does not contain nitrogen.

Review and Preliminary Investigation into Fuel Loss from Cermets Composed of Uranium Nitride and a Molybdenum-Tungsten Alloy for Nuclear Thermal Propulsion Using Mesoscale Simulations

“…To reduce fuel loss in UN cermets by reducing the production of free U, we must reduce the hightemperature decomposition that occurs in UN. [23][24][25] As mentioned in Sect. 2, this could possibly be accomplished with additives to UN, similar to the strategy of adding oxides to UO 2 to stabilize its structure.…”

“…Various researchers have established that UN experiences a decomposition reaction at high temperature and low N partial pressure, producing liquid U and N 2 gas. [21][22][23][24][25] At lower temperature and higher N partial pressure, UN forms the U 2 N 3 phase. 21,22 Early N release starts at 1600 K, and precipitation of liquid U begins at 2120 K. 24 This decomposition likely could cause release of U from the fuel kernel and diffusion into the metal matrix grain boundaries, which will contribute to fuel loss.…”