Antineutrino Detection Techniques for Monitoring Long-Term Geological Repositories

The radioactive nuclear waste produced in the past decades contains many significant quantities of plutonium, one of the key ingredients for manufacturing nuclear weapons. For the first few hundreds of years after discharge, the dominant radioactivity of the waste comes from long-lived beta-decaying elements, in particular Sr and Cs. In this paper, we discuss the prospects of safeguarding long-term geological nuclear waste repositories by detecting the low-energy antineutrinos emitted via beta-decays. We investigate whether these antineutrino measurements could be carried out with time projection chambers, for example using liquid argon. In contrast to the typical scintillation or water-Cherenkov detectors, this emerging technology could detect antineutrinos even below the inverse beta decay kinematic threshold, i.e. the typical energy range for radioactive waste emissions. Furthermore, due to their imaging properties, time projection chambers could also provide directional ity information which may be used for background rejection and potentially also for indicating if and where a certain amount of nuclear waste has been diverted. We present a first feasibility study for employing liquid-argon detectors for safeguarding geological repositories. We consider a realistic repository layout as a study case and evaluate the detector performance in this context, from first principles.