The THOREX process

The solvent extraction cycles employed for the THOREX process have the same general features as those utilized in the PUREX process. However, there are some important major differences in the process chemistry and flow conditions used for the two processes. First, the separation of thorium from uranium is more difficult than the separation of plutonium from uranium. In the PUREX process, the plutonium can be be adjusted to the relatively inextractable +3 valence state to effect its separation from uranium. Valence change to effect thorium separation is not possible because of the high stability of Th4+. Secondly, higher organic-to-aqueous phase ratios are required in the THOREX process because of the limited solubility of the TBP·Th(NO3)4 adduct and of the significantly lower extractability of Th(NO3)4 relative to plutonium and uranium nitrates. This chapter covers: history of THOREX process; chemistry of THOREX process; recovery of uranium 235 from low burnup ThO2 targets; and recovery of uranium 233 from fuels of high burnup and/or high uranium content