  The recent agreement to transfer nuclear submarine reactors and technology
from two nuclear-weapon states to a non-nuclear-weapon state (AUKUS deal)
highlights an unsolved problem in international safeguards: how to safeguard
naval reactor fuel while it is on-board an operational nuclear submarine.
Proposals to extend existing safeguards technologies and practices are
complicated by the need for civilian international inspectors to gain access to
the interior of the submarine and the reactor compartment, which raises
national security concerns. In this paper we show that implementing safeguards
on submarine propulsion reactors using a low-energy antineutrino reactor-off
method, between submarine patrols, can by-pass the need for on-board access all
together. We find that, using inverse beta decay (IBD), detectors can achieve a
timely and high level of assurance that a submarine's nuclear core has not been
diverted (mass of around 100 kg) nor its enrichment level changed (mass of
around 10 tons).
