Hopefully has protection from disassembly.
To be clear the "detonation" is NOT the nuclear material going critical, or even a "dirty bomb" type explosion. It is akin to thermite on the electrical firing ICs/circuits to completely destroy the intelligent logic of managing the conventional explosives that triggers the nuclear material.
PU239 has a half life of 24,110 years and that's your best case for a dirty bomb, if the core is U235 then it has a half life of 703,800,000 years which means when it's not in any substantial mass in which the nuclear decay is can to turn into a chain reaction it's about as radioactive as cat litter or a banana.