Environmental assessment of advanced partitioning, transmutation, and disposal based on long-term risk-informed regulation: PyroGreen

The safety of spent nuclear fuel (SNF) storage has become one of the major issues of nuclear power plant operation. Direct disposal and recycling have both been criticized by the general public due to uncertainty of the long-term safety of SNF and high level waste (HLW) repositories. To meet the goal of sustainable nuclear energy, an innovative recycling approach using pyrochemical partitioning and transmutation termed PyroGreen, which is a conceptually advanced pyrochemical partitioning flowsheet, has been proposed to eliminate the need for HLW repositories. From the previous partitioning process, PyroGreen uses a combination of hull electrorefining, reductive extraction, and selective oxidation to further decontaminate SNF and HLW into low- and intermediate level waste (LILW). This paper examines the long-term environmental performance of a geological repository that houses all of the final PyroGreen-produced wastes while describing the feasibility of PyroGreen partitioning and transmutation. The final PyroGreen wastes are evaluated based on long-term risk-informed criteria: alpha-emitting isotope concentration, heat generation, and radiation dose in the surrounding biosphere. All final wastes arising from PyroGreen are to be disposed of in a geological repository at an intermediate depth, in compliance with new International Atomic Energy Agency Safety Guide for LILW. Migration assessment found that several long-lived fission products including C-14, Cl-36, Se-79, Sn-125, and I-129 dominate the long-term dose rate, whereas transuranic elements govern the risk of an inadvertent human intrusion scenario. In order to turn entire batches of SNF from 24 light water reactors with 1000 MWe with a design life of 40 years into LILW, we determined and compared the required decontamination factors of the key radionuclides for between intermediate-depth and near-surface disposal.