The effect of temperature on water uptake, swelling and void formation in a bitumen matrix with ion exchange resins

Experimental studies have been performed to study the effect of temperature on the rate of water uptake into a simulated waste form of dehydrated ion exchange resins in bitumen. The studies involved the determination of weight increase, and the investigation of specimen samples in a scanning electron microscope after different storage times in water. The storage time varied between one day and one month. The experiments were performed at 3, 20 and 30 °C, and for dry resin contents of 40, 50, 60 and 70 weight %. No effect of temperature was observed for 40% resin. The important result is the observation that for the specimens with resin contents of 50 and 60% the rate of water uptake and swelling were much faster at 3 °C than at the higher temperatures. A plausible explanation is cracking of the matrix due to the brittleness of bitumen at low temperatures. In conclusion, these screening tests seem to indicate the need for more careful consideration of the ductility of bitumen and its temperature dependence when establishing the acceptance criteria for bitumenized radioactive waste.