Opportunities and risks of partitioning and transmutation of the long-lived fission product I-129

The radioactive isotope of iodine, I-129, is among the radionuclides in spent nuclear fuel (SNF) which pose the highest risk of long-term radiation release into the biosphere from the final SNF repository, mainly due to its very long half-life, about 16 million years, and its relatively high mobility. Several possibilities to minimise this risk were proposed in the literature, e.g. additional barriers in the final repository, vitrification or transmutation. The latter two approaches however require the chemical partitioning of SNF, which can lead to additional discharges of radioactive substances to the biosphere. The purpose of this work is, on one hand to estimate the transmutation times, rates and efficiencies of I-129 in different types of irradiation facilities, including thermal and fast reactors, accelerators and lasers, and on the other hand compare the typical releases of I-129 during partitioning and transmutation to the reduction of its inventory by transmutation. The transmutation times were calculated based on typical neutron fluxes and spectra, adopted from the literature, in corresponding irradiation facilities. In addition, for some specific examples with typical light-water reactor fuel, absolute transmutation rates were calculated using a 2D Serpent model of a fuel assembly. Thereby, in addition to the assessment of the I-129 transmutation, its impact on the reactor operation can be observed. In all calculations, nuclear data from the ENDF/B-VII.1 library were used.