Kinetic and microstructural studies of thermal decomposition in uranium mononitride compacts subjected to heating in high-purity helium

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.…”

“…[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. Thus, the reactions that will take place in a UN cermet, similar to the UO 2 reactions from Eqs.…”

Lead-Cooled Fast Reactor Annular UN Fuel Design and Development of Performance Analysis Program

“…The fuel design described in this paper targets to resolve the inherent deficiencies of the fuel and enable the fuel to operate over an extensive fuel life. Although the UN fuel has a very high melting point, it will start to decompose at about 2000 K due to low partial pressure of nitrogen (Bo et al, 2012;Lunev et al, 2016). Therefore, the fuel pellet temperature should be kept strictly below 2000 K when the reactor is in operation.…”

“…Uranium nitride, as the main form of nitride nuclear fuel, is superior to conventional oxide fuels (MOX, UO 2 ) in multiple ways (see Table 1): it possesses higher heavy metal density as compared to oxide fuels, increasing the conversion ratio (CR); it has better thermal conductivity; the thermal conductivity increases as the temperature increases, which provides the fuel with better performance under transient conditions; and the fissile inventory ratio of UN is 10% higher than that of MOX fuel (Bo et al, 2013). However, the performance of UN fuels also suffers from two important drawbacks: severe fuel swelling and thermal decomposition at high temperature, which tend to limit the development of UN fuel applications in fast reactors (Bauer et al, 1979;Lunev et al, 2016). In order to achieve better performance of UN fuel in fast reactors, this paper is targeting to resolve the above issues by carrying out a new kind of annular fuel design.…”