Mass spectrometric study of the release of volatile fission products from irradiated LWR fuel

The chemical form and rate of release of volatile fission products (i.e., Xe, Kr, Cs, Te, and I) effused from a section of an irradiated LWR fuel pin are being studied using quadrupole mass spectrometry. The released volatile fission products must effuse through a hole drilled in the cladding to reach the ionizer of the mass spectrometer. Experiments to a temperature of 14500C have identified krypton, xenon, cesium, tellurium, and atomic iodine (very weak signal) as the species released from the fuel. The source of the atomic iodine, i.e., dissociation of cesium iodide or dissociation of molecular iodine, has yet to be resolved. The observed rate of release of xenon is several orders of magnitude lower than previously reported. In complimentary experiments on nonradioactive material, the reaction of tellurium with the zircaloy cladding was found to hinder its release. Above 12000C, gaseous SnTe was observed; its formation is attributed to reaction of the tin (in the cladding) with ZrTe2