Reactions and products in the Cs-Zr-I-O system relevant to fission product chemistry - a review

Some results and problems associated with the known chemistry of cesium and iodine in the presence of Zr/ZrO₂ at 400-600°C and under anaerobic conditions are described and discussed. These aspects include 1. (1) the recently synthesized cesium zirconates Cs₂ZrO₃ and Cs₄ZrO₄ and some of their thermal and hydrolytic properties 2. (2) the demonstration that the supposedly stable CsI reacts with ZrO₂ at 400-700°C to form Cs₂ZrO₃ and ZrI₄ (as Cs₂ZrI₆) and its implications regarding cesium and iodine distributions 3. (3) present knowledge of binary zirconium iodides, their contamination reactions, and the limited inhibition of the reduction of ZrI₄ by metal provided by static ZrO₂ films 4. (4) newly discovered ternary and quaternary zirconium iodides that are obtained in the presence of many common impurity atoms and, when prsesent, CsI (e.g., Zr₆I₁₂C, CsZr₆I₁₄C, Zr₆I₁₄Fe), the ease with which some of those form at least as low as 450°C, and the complications these and related new phases provide.