1. A method of operating a nuclear reactor with the aid of a digital computer, comprising: (a) providing said computer with a data base including at least a list of safe reactor states, said safe reactor states being those combinations of individual reactor component states which are safe wherein said individual reactor components states are expressed as the binary notation (ab) where `a` defines the status of the components control switch and `b` defines the status of the component and wherein said list of safe reactor states is determined by combinatory logic operations upon said binary notation expression of said individual reactor component states, and a list of control instructions for achieving a safe reactor state; (b) repetitively determining the actual states of said individual reactor components; (c) repetitively providing the computer with said actual component states; (d) repetitively comparing in the computer said actual component states with said list of safe reactor states; (e) selecting in the computer operating instructions for achieving a safe reactor state from said list of control instructions when a said comparison indicates that said actual component states do not match a said safe reactor state; and (f) executing said operating instructions.