Accountable Nuclear Material Production From Fissile Isotope Precursors In Advanced Fuel Cycles: The Case Of Protactinium-233

Introduction of thorium into nuclear fuel cycles has been proposed to improve fuel efficiency and reduce production of long-lived radioactive waste from nuclear power. Protactinium-233 is produced during the neutron irradiation of thorium-232 in a nuclear reactor. Protactinium-233 is a short-lived precursor to the fissile isotope uranium-233, and forms upon neutron irradiation of thorium-232 in a nuclear reactor. Protactinium-233 β- decays with a 27-day half-life to uranium-233, which is an accountable nuclear material under international nuclear safeguards. However, protactinium-233 itself is not an accountable nuclear material; therefore, there are no conceptual approaches for monitoring protactinium-233 during thorium irradiation and spent fuel reprocessing. In this paper, we argue that technological advances in nuclear fuel cycles, particularly those related to rapid or online spent fuel partitioning, may result in the need to monitor fissile isotope precursors to meet accountancy and timeliness goals for nuclear materials. First, we will describe a “Goldilocks” approach used to identify protactinium-233 as a high-priority fissile precursor material. We then approximate the quantity of protactinium-233 generated in an example thorium-fueled reactor from first principles, showing that sufficient quantities of protactinium-233 will be generated to impact uranium-233 materials accountancy, depending on spent fuel partitioning timelines. Finally, we suggest a framework for developing safeguards approaches for nuclear materials and their precursor material counterparts that may apply to isotope pairings beyond protactinium-233 and uranium-233.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2021-2950 A