Study of the retention of Ba in UO2 nuclear fuel particles by ZrO2 as getter

A new concept to retain solid fission products in the coated particles of gas-cooled high-temperature reactors is the addition of refractory oxides to the fuel kernels as a getter. The suitability of this concept for the retention of BaO by ZrO₂ was determined. Therefore, the evaporation of BaZrO₃ was studied by high temperature mass spectrometry with a Knudsen cell made of Mo and the loss of Ba from model kernels heated for 100 h at different temperatures in a furnace was determined. From the results obtained with each of the two methods which were carefully discussed by theoretical considerations it follows independently that Ba can be retained by ZrO₂ but that Al₂O₃ is even more efficient for the retention of Ba than ZrO₂. Moreover, it could be shown that BaO is the main species in the gaseous phase over BaZrO₃.