We propose, apply, and verify a screening approach for the selection of safety-relevant radionuclides that should be tracked in models assessing the performance of geologic repositories for the disposal of spent nuclear fuel and high-level radioactive wastes. Starting with a comprehensive list of radionuclides present in the waste form, a multi-step down-selection process evaluates each isotope’s potential relative contribution to the total peak exposure dose, which is a surrogate metric for ove