This model is based on photographs found on the Internet. There appear to be two shapes of containment vessel, a rectangular design and a longish cylinder between two rectangular end sections. I chose to model the latter because it is visually slightly more interesting.
The wagon is of massive construction, presumably because of the mass of the shielding material in the vessel, and has two bogies at each end, although I decided to simplify this to just one, to economise on parts.
The flanged wheels on the model are 3D-printed, and are a push fit on the axle rods. The circular shape of the centre section of the vessel is maintained by three internal discs, also 3D-printed.