So, a small nuclear pile, with a control box that can be operated manually, and extremely rarely, a working automated control box.
If stationary, you set it up, insert moderating rods, some nuclear material, and water, and off you go. If you don’t attend to it (adjust the rods) at least once or twice a day, the reactor takes damage. After a bit, it explodes, destroying everything around it, and preferably leaving a radioactive zone. The water is needed as part of the turbine apparatus, and so perhaps consume 10-20 water per day or more. If used on a vehicle and it becomes damaged, it leaks radioactivity, and there is a clear risk of overload, and you have a chance to fail at raising the control rods. Tuck and roll baby.
With the new power cables, it could be used to connect to any number of devices, but maybe has to be used to charge a battery and can’t be used directly.
Maybe the apparatus could be used in a “low thermal state”, which doesn’t destroy itself, but releases heat so you can survive in winter. It irradiates you if the furnace is broken, and has a chance of overload if the rods are damaged.
The automated box may only be found in a nuclear silo or power plant or something, and although it gets rid of the moderation need, it does not change the water need.
Ultimately I’d imagine one could find them at the engines of trains, 100% of the time damaged, and only after the first or second incident you realize turning on broken nuclear-powered trains is a bad plan.