Radioelements in irradiated fuel
Spent fuel is an extremely complex system, due to the diverse nature of its constituent elements. Most radioactive atoms are trapped by the uranium oxide pellets inside the irradiated fuel rods. A few gaseous or mobile fission products (such as caesium, iodine, technetium or tritium) may be present in the gap between the pellets and the cladding. The role of the cladding is to prevent leaks.