“Spent fuel Dissolution in Supercontainer conditions” Period 2012-2014

This report presents the results for the period 2012-2014 of the research programme “Spent fuel dissolution in Supercontainer conditions” to assess the stability of spent fuel in the highly alkaline chemical environment of the Belgian Supercontainer design. We first confirmed the results obtained for the period 2009-2012 [ER-231], so far as concerns the UO2 dissolution at high pH conditions. We also demonstrated that the depleted UO2 is representative for “old” spent fuel, and we refined the domain of the alpha-threshold for the oxidative UO2 dissolution at pH 13.5. Based on new dynamic rates, we proposed an updated dissolution rate ranges. However according to our current experiments, we cannot state about the possible inhibiting dissolution effect of hydrogen concentrations at pH 13.5 with Pu-doped UO2. Based on more fundamental experiments, we also succeeded to better characterize our initial fuels, to improve the preparation of our cementitious water as well as the results of the U analysis, and to get more insight on the possible interaction between U and cations (Ca, Na and K) present in cementitious systems based on experiments in TMAOH (tetramethylammonium hydroxide) solutions.