Probably an incredibly stupid question but I've always wondered why we can't take small amounts of nuclear waste - say, size of a AA battery, put it into a metal package and use it in laptops / cars / whatever. Short of the risk of leakage, the amount of power that can be generated from it is surely enough to power a laptop or put them into a battery pack for a car, no ?
That's the main risk. A major cause of civilian radiation accidents is radioactive material accidentally mixed with unlabeled scrap [1], and if you put any noticeable amount of the stuff into products meant for untrained civilians, the rate of that happening would skyrocket.
I'm not an expert but I know of two different technologies to convert heat to power: thermocouples and heat engines.
Thermocouples are great because they're small, can fit in enclosed spaces, have no moving parts and last nearly forever. However, they're not a very efficient way to convert heat to energy.
Heat engines + generators can be very efficient, but they're bulky and have many moving parts (you're not going to attach a diesel generator to your cell phone).
