I have found a possible bug that creates a race condition in the reactor. If you cut power to the reactor while it has fuel in it, the reactor will continue to run as if the fuel is being burned. During this time the fuel is not used up, but the reactor still heats as if the fuel is being used.
I had wired up my reactor so I could cut power to it and the feeding inserters when the output tanks of hot water were full. However, when the full condition did occur, my reactors actually continued to heat the water for free.
This makes it impossible to shutdown a reactor in this state, and offers unlimited free hot water with no fuel costs.
