One of the isotopes that we're facing (if things crack and go nuts) is the radioisotope Iodine-131.
I'm learning all kinds of interesting stuff about chemistry and physics (with respect to the wind and movements of particles):
131I decays with a half-life of 8.02 days with beta and gamma emissions. This nuclide of iodine atom has 78 neutrons in nucleus, the stable nuclide 127I has 74 neutrons. On decaying, 131I transforms into 131Xe:
The primary emissions of 131I decay are 364 keV gamma rays (81% abundance) and beta particles with a maximal energy of 606 keV (89% abundance).
The beta particles, due to their high mean energy (190 keV; 606 kev is the maximum, but a typical beta-decay spectrum is present) have a tissue penetration of 0.6 to 2 mm.
131I is a fission product with a yield of 2.878% from uranium-235, and can be released in nuclear weapons tests and nuclear accidents. However, the short half-life means it is not present in significant quantities in cooled spent nuclear fuel, unlike iodine-129 whose halflife is nearly a billion times that of I-131.