Detection of Methyl Iodide upon Heating Irradiated Fuels

Laboratory scale experiments have been carried out to obtain information on the sources of CH3I, reported by various workers to have been detected under accidental conditions of fuels. Small pieces of slightly irradiated sintered UO2 and U metal turnings were heated externally up to 1,400° C in various carrier gases, and the carrier gases were analyzed for fission product iodine present in the form of CH3I. From the data obtained, it is concluded as follows: In the case of sintered UO2, some amount of CH3I appears to be released directly from the fuel below 600°C, whereas in case of U metal turnings, direct release does not apparently occur at any temperature. In oxidizing atmospheres, iodine released from either sintered UO2 or U metal is considered to change into CH3I only to a small extent, probably by gas phase formation.