Fission product release from spent nuclear UOX fuel dissolution: Comparison between anoxic and reducing conditions and impact of pH

Several clad segments from the same spent nuclear fuel rod were leached in a highly alkaline solution representative of the conditions expected in the current Belgian reference deep disposal design, and in presence of hydrogen. The results are compared with experiments that were conducted with clad and declad samples in a bicarbonate solution without presence of hydrogen. For the monitored radionuclides (²³⁸U, ⁹⁰Sr, ¹³⁷Cs, ¹²⁹I, ⁹⁹Tc), a fast initial release was observed. Afterwards, the release depended on the experimental conditions (medium, redox conditions) for uranium, strontium and technetium, but not for cesium and iodine. The cumulated released fractions were quantified at the end of the experiment. Graphical Abstract: (Figure presented.)