The spent fuel does not contain weapon-grade uranium (highly enriched uranium, HEU) so would not be shipped for nuclear non-proliferation reasons.
Letter from DOE to NRC, November 30, 2018 – linked here
The U.S. Department of Energy (DOE) requests renewal and simple amendment ofNRC Certificate of Compliance (CoC) 9330 for the Model ATR FFSC (NRC Docket 71-9330), no later than January 11, 2019. An amendment to the CoC is necessary to add the fuel element for the Greek GRR-1 reactor to the list of authorized contents.
The GRR-1 reactor facility in Greece is in the process of decommissioning. The reactor is an open-pool materials test reactor (MTR) using aluminum plate fuel. The facility is in possession of 13 unirradiated plate fuel elements of the same type as the approved contents of the A TR FFSC. Each element contains up to 223 g U-235, enriched up to 20 weight percent. The fissile material is uranium silicide (U3Sb) dispersed in aluminum powder. The element has 18 fuel plates held in place by two aluminum side plates and end fittings. Each fuel plate consists of the central “meat” of fissile uranium silicide nominally 0.02 inches thick. The cladding is nominally 0.02 inches thick and is made from aluminum alloy AG3NE.