Constrain the sintering of UO2 target through the usage of a dual-phase interpenetrating microstructure

The Isotope Separation On-Line (ISOL) technique is an established method to produce isotopes of interest in the form of Radioactive Ion Beams, which are increasingly in demand. The isotopes are produced within a target material through nuclear reactions initiated by the collision of an incident beam. The isotopes must then be released from the target via diffusion and effusion in order to be extracted, isolated, and transported to its final destination; either an experiment or a collection apparatus. The operating conditions require the ISOL target material to withstand high temperatures, typically around 2000 °C, high radiation damage and vacuum conditions. Uranium dioxide (UO2), with its high melting point, is candidate as an ISOL target material and has been used and discarded in the past. This was mainly due to its fast sintering at high temperatures which reduces its suitability for producing high-quality Radioactive Ion Beams without compromising their yields. This work aims to hinder the sintering of UO2 by developing an interpenetrating dual-phase microstructure that stabilizes grain growth at elevated temperatures, enabling its potential use as an ISOL target material in the future ISOL@MYRRHA facility. Magnesium oxide (MgO) and aluminum oxide (Al2O3) have been studied as secondary phases to limit UO2 grain growth at high temperatures. To study the insolubility of UO2 and the sintering behaviour at elevated temperatures of UO2 mixed with MgO and Al2O3, pellets with various volume ratios were prepared and sintered at 1650 °C for 1 hour under two different atmospheres: argon and a reducing atmosphere with a potential of -420 kJ/mol. The sintered pellets were characterized by means of X-ray diffraction, density measurements, and scanning electron microscopy. Although densification still happened, both MgO and Al2O3 proved to be insoluble in UO2, forming two distinct phases and significantly reducing UO2 grain growth.