Sweden and Finland are preparing for final deposition of spent nuclear power fuel. The adopted method is to encapsulate spent nuclear fuel in copper canisters filled with iron before deposition in a deep bedrock repository. The canisters will have a diameter of about one metre, which makes examination of the content in sealed canisters virtually impossible with any known technique today. Two methods for tomography of sealed canisters have been studied, high-energy neutron tomography and cosmic-ray muon tomography. Monte Carlo simulations using MCNPX have shown that it would indeed be possible to produce images of good resolution of thick massive objects, like these canisters, using high-energy neutrons. The cost for installing such a method would, however, be very high. GEANT simulations, supported by experimental tests, indicate that tomography using the natural flux of cosmic-ray muons results in images of lower quality, but to a much more modest cost, acceptable to the application. Figure 1: Canisters for spent BWR nuclear fuel. The canister consists of a cylindrical copper shell with a pressure-bearing insert of nodular iron. The outer diameter is 1.05 m and the length 4.83 m [1].

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