Retention of cesium and strontium by uranophane, Ca(UO2)2(SiO3OH)2·5H2O

Highlights: • The sortion of cesium and strontium onto uranophane is studied separately. • The sorption process is fast in the two cases studied. • Uranophane showed high sorption capacity for cesium and strontium. • The sorption process depends on the ionic strength used. - Abstract: This work determines the capacity of uranophane, one of the long-term uranyl secondary solid phases formed on the spent nuclear fuel (SNF), to retain radionuclides (cesium and strontium) released during the dissolution of the SNF. Sorption was fast in both cases, and uranophane had a high sorption capacity for both radionuclides (maximum sorption capacities of 1.53·10⁻⁵ mol m^-2 for cesium and 3.45·10⁻³ mol m⁻² for strontium). The high sorption capacity of uranophane highlights the importance of the formation of uranyl silicates as secondary phases during the SNF dissolution, especially in retaining the release of radionuclides not retarded by other mechanisms such as precipitation.