  International nuclear safeguards inspectors do not have a method to verify
the contents of sealed storage casks containing spent reactor fuel. The heavy
shielding that is used to limit radiation emission attenuates and scatters
photons and neutrons emitted by the fuel, and thereby hinders inspection with
these probes. This problem is especially pressing given the policy decisions of
several nations to begin permanent disposal of spent fuel in deep geological
repositories. Radiography with cosmic-ray muons provides a potential solution,
as muons are able to penetrate the cask and fuel and provide information on the
cask contents. Here we show in simulation that muon scattering radiography can
be used to inspect the contents of sealed geological storage casks, and can
discern between a variety of plausible diversion scenarios. This technique can
be applied immediately prior to permanent interment in a geological repository,
giving inspectors a final opportunity to verify State declarations of spent
fuel disposal.
