Disclosed is an apparatus, system, and method for monitoring a position of a control rod disposed in a nuclear reactor vessel in a radioactive environment. A data processing unit located outside a containment structure includes a processor and a memory storing executable instructions. A nuclear reactor vessel includes a plurality of control rods proximate to the control rod and a coil stack of a plurality of control rod position indicator coils. A data cabinet mounted on the nuclear reactor vessel head inside the containment structure includes an analog multiplexer and a communication circuit. The processor executes the instructions to select a control rod position indicator coil through the analog multiplexer, pass a signal from the control rod position indicator coil through the analog multiplexer, receive the signal from the analog multiplexer through the communication circuit, and determine a position of the control rod based on the received signal.