Reactive distillation process using a solid-solid reaction for the separation of strontium from spent nuclear fuel

Abstract

The separation of high-heat-generating isotopes of Sr from spent nuclear fuel is a significant research area in nuclear waste management. To separate Sr from spent nuclear fuel, the chlorination method using MgCl2 is known to be very effective. Then, the separated Sr must be oxidized for the solidification process, for example by oxidation using K2CO3, but this faces challenges owing to the high reactivity of MgCl2. Thermodynamic calculations and experiments demonstrated that MgCl2 has a higher reactivity with K2CO3 than SrCl2, forming MgO instead of SrO. This study therefore investigated a novel two-step reactive distillation process employing solidsolid reactions with K2CO3 for the first time. The first step is to completely distill MgCl2 from the mixture of MgCl2 and SrCl2. Then, the second step involves the addition of 1.7 molar equivalents of K2CO3 to the residue after the distillation of MgCl2, in order to obtain SrO through reactive distillation using a solid-solid reaction with SrCl2. This study confirms that this method is effective as the next step in the Sr separation utilizing MgCl2, and by applying the reactive distillation process to oxidize Sr for the first time, it has contributed to completing the Sr separation process using molten salts.