Control rod housing alignment apparatus

In a boiling water nuclear reactor having its core, fuel support casting, and control rod guide tubes removed to expose the core plate, an apparatus for the repair and replacement of the control rod drive housing at the bottom extremity of the reactor vessel is disclosed. The apparatus registers to a hole in the core plate and its corresponding guide pin. A mating fixture on the depending extremity of the shaft of the apparatus precisely fits and mates to the top of the control rod drive housing. The alignment device includes cross electronic levels sealed for submersion which levels remotely transfer through attached wiring the precise angularity between the top of the control rod drive housing on one hand and the corresponding and overlying hole in the core plate on the other hand.