Comment by numpad0

The simplest form of a nuclear reactor is some small sphere of purified heavy metal put onto a cavity on a thick Be sphere and covered by another piece of the same metal. The reactor can be started up and shut down by lowering or lifting the top piece using a flathead screwdriver shoved between two pieces, which can kill anybody nearby if dropped and the pieces go ultra super critical. That has to be a lot simpler than even a basic solar cell by itself.