High Temperature Uranium Nitride Decomposition

Abstract

Thermal stability of the sintered samples of uranium mononitride was investigated in high purity helium atmosphere at 1900° – 2300°С. Thermogravimetry analysis of samples showed that the weight loss in uranium nitride consists of two stages. On first stage decomposition of uranium mononitride and nitrogen release starts. On the second stage additional active evaporation of uranium metal happens. During heating of the samples, nitrogen was registered by mass spectrometry. Microstructure of the samples after high temperature tests showed irregularly distributed spherical particles of uranium metal.

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.…”

“…where A ¼ 2:617 Â 10 5 , B ¼ 5:476 Â 10 5 , R is the ideal gas constant in J molK , and T is the temperature. A and B are obtained from an exponential fit to experimental data, 23 as shown in Fig. 8.…”

Modeling of Phase Separation in Uranium Mononitride

“…Previous experiments [3,4] using Netzsch STA 449F1 (synchronous thermal analysis device) showed that decomposition on the surface of the samples with the precipitation of liquid uranium is occurs as a result of heating uranium mononitride in helium.…”

“…thermodynamically However, when considering the kinetics, the modeling will change dramatically. In this paper, modeling based on chemical kinetics was conducted, using the experimental data of uranium mononitride decomposition obtained earlier [3,4]. …”