Nuclear fuel pellets for fission reactors are produced through a complex process in which raw material powders are conditioned, pressed and sintered, to achieve the industrial desired density (95-98 %). The raw material properties such as particle size, shape, specific surface area, porosity, bulk density, flowability, etc. determine the stability of the pressed pellet and its sinterability. Improving the raw material conditioning step smooths the complete process.
Hence, a reliable and detailed determination of textural properties of the nuclear fuel raw material is essential. Gas isotherms allow to measure the total pore volume and to calculate through well-known mathematical models the specific surface area, micropore volume and pore size distribution. The surface area and porosity of nuclear fuel materials e.g. uranium oxide, thorium oxide, etc. have usually been investigated using the N2 adsorption isotherms at 77.4 K. The N2 molecule is a specific adsorptive having a quadrupole moment, where the specific interaction between the quadrupole moment of N2 molecule and functional groups on solid surface or charges in the channels of the material may occur. Moreover, other gases as Argon atom, can be used to perform the Ar isotherm at 77.4K. The Ar atom is a nonspecific adsorptive, where van der Waals interaction is the main factor in the Ar adsorption, and the surface functional groups or charges in channels may have little influence on the Ar isotherms.