While it's a neat point that you bring up about human nature and misplaced radioactive sources, is a portable nuke reactor something that's comparaable to radiotherapy units?
If what they mean is a Small Modular Reactor, they should still be about 40 m^3, and a bit less likely to be left behind.
If what they mean is a Small Modular Reactor, they should still be about 40 m^3, and a bit less likely to be left behind.