Dissolution tests using ThO2 microspheres, ThO2 pellets, and Zircaloy tubing were performed to establish conditions that can be used for the selective dissolution of thoria from Zircaloy cladding. Although additional work is needed in several areas, the following conditions are tentatively recommended for use in process demonstration tests: 0.02 to 0.04 M HF in refluxing 8 to 12 M HNO3 with sufficient Al3+, or (preferably) Zr4+, added to prevent major corrosion of the stainless steel dissolver vessel. If Zr4+ is used, the concentration required is approximately the same molarity as the fluoride concentration.