There is no way to do that. We can extract nuclear energy only as heat, and then we convert this heat to energy. There is no known way to change this ever, although it is theoretically not impossible.
If we have a heat-power machine, that will make everything large. You can not have a mobil phone driven with such a machine, it will be at least kilos or more. That is because as you decrease the heat-power converter, so will it be lesser effective, due to the heat conduction loss.
Thus, either we have everything embedded with a turbine generator, or we have some wizardry which can generate directly electric current from decaying uranium.
Now case is that there is no way to create a nuclear bomb from nuclear fuel. Either you need fuel refined, reprocessed exactly for that, or you need to essentially mis-use power producing nuclear reactor. Some facts:
- Ordinary uranium has 0.7% fissile isotope, for bomb-grade Uranium it must be enriched above 90%, but for reactors only 3% is enough.
- Plutonium bomb needs Pu-239 isotope. That is not available in the nature, but is produced in nuclear reactors. However, in nuclear reactors, also Pu-240 and Pu-241 is being produced, which poisons the bomb. There is no economical way to separate Pu isotopes. Thus, the only way to create Pu-239 if you turn off the power producing reactor before too much higher Pu isotope would be created. That needs a power producing nuclear reactor where the fuel can be replaced while work, most of them are not. It also needs a nuclear fuel reprocessing plant which is more costly as the reactor itself.
Thus, I believe, proliferation would not be threatened.
Dirty bomb could be easy to create. And probably not what you want to have, if your car leaks and the molten fuel pours to the asphalt. There are many ways to prevent also that, though.