Evaluation of the Cs-Mo-I-O and Cs-U-I-O diagrams and determination of iodine and oxygen partial pressure in spent nuclear fuel rods

This work provides three dimensions potential diagrams calculated in view of the evaluation of the iodine partial pressure in spent PWR fuel pellets intended to be stored for 100 years. These diagrams can be interpreted, on the basis of spent fuel examinations. It is shown that the iodine partial pressure could be controlled by the formation of cesium uranate Cs2UO4 from cesium iodide CsI in the fuel. If the formation of cesium molybdate Cs2MoO4 would take place during the storage, the iodine partial pressure is expected to increase. Such an evolution can't be excluded because of the temperature that could reach the spent fuel assemblies during the transport step up to the place of the storage.