Since the radioactive waste is
composed of fission products, the main sources of radiation are beta and gamma
rays from the decay processes of the isotopes. The beta particles (electrons)
can be stopped by less than a millimeter of material. The gamma rays require a
much greater mass to stop them.
The waste canister must be wrapped
in a gamma ray shield as well as a mechanical protection wrap. These additional
wraps around the canister will add a very large amount of mass to the overall system,
and all of this mass must be transported to space. For this reason, it becomes extremely
important to shape the basic canister in such a way that the required additional
packaging is at a minimum.