The seams would be in the walls of the water containment vessel, which could be any shape. All you have to ensure is that the total travel distance through water is 1 meter or more in any direction.
Of course you could bury the thing underground and not worry about shielding it with water. That is until you have to service it. Depending on the surrounding material you may encounter some neutron activation. i.e. the neutrons have made the material radioactive.
That residual radiation should be rather small, after all it is mostly aneutronic fusion. In the end, however, I would expect that water (with a blanket of boron) provides the cleanest solution.
