Nuclear reactor power supply

The redundant signals from the sensor assemblies measuring the process parameters of a nuclear reactor power supply are transmitted each in its turn to a protection system which operates to actuate the protection apparatus for signals indicating off-process conditions. Each sensor assembly includes a number of like sensors measuring the same parameters. The protection system has a number of separate protection units, each unit receiving the process signals from the like sensors of each assembly in its turn. The sets of process signals derived from the sensor parameter assemblies are each in its turn transmitted from the protection system to the control system which impresses control signals on the reactor or its components to counteract the tendency for conditions to drift off-normal status requiring operation of the protection system. A parameter signal selector is interposed between the protection system and the control system. This selector prevents a parameter signal of a set of signals, which differs from the other parameter signals of the set by more than twice the allowable variation of the sensors which produce the set, from passing to the control system. The connection between the protection units and the selector is four separate fiber optic channels so that electrical interaction between the protection units and the selector or control system is precluded. The selectors include a pair of signal selection units, one unit sending selected process signals to primary control channels and the other sending selected process signals to back-up control channels. Test signals are periodically impressed on a selected pair of a selected unit and control channels. When test signals are so impressed the selected control channel is disabled from transmitting control signals to the reactor and/or its associated components