High temperature Knudsen cell mass spectroscopy studies on dysprosium-doped uranium dioxide

Atomic Energy of Canada Limited (AECL) has developed a new type of CANDUR fuel that includes one or more fuel elements in the fuel bundle with dysprosium (as (U,Dy)O2)) as a burnable neutron absorber to control the reactor reactivity. Experiments were carried out to study the volatility of dysprosium-doped fuels at high temperatures using Knudsen Cell-Mass Spectrometry (KC-MS). Experiments were performed at temperatures up to 2500 K for (U,Dy)O2 fuel samples with different dysprosium concentrations between 0 and 14.9 Dy wt.%. The KC-MS results suggest that the total vapour pressures of dysprosium and uranium in (U,Dy)O2 samples appear to follow Raoult's law i.e., the dysprosium-doped fuel samples behaved like solid solutions. The vaporization behaviour of uranium species in (U,Dy)O2 fuel, within the dysprosium concentration range ≤ 14.9 Dy wt.%, appears to be similar to that observed in the standard CANDUR fuel. The vapour pressures of dysprosium species were about more than one order of magnitude lower than those of uranium species. It is concluded that the volatility of dysprosium present in (U,Dy)O2 fuel will not cause any significant problem in CANDUR reactors. (authors)