In-core monitor driving mechanism

A driving mechanism for moving a detector vertically through a pressure vessel in a direct manner in order to measure the neutron flux distribution is improved by installing directly below the in-core housing a motor adapted to move a detector-tipped drive shaft through the vessel. The driving mechanism includes the motor which is equipped with a hollow rotary shaft through which the drive shaft is inserted, and a worm, gear and sprocket arrangement for converting rotational motion of the shaft to linear motion of the drive shaft so as to move the drive shaft vertically through the rotary shaft and guide pipe and into the pressure vessel. This obviates the necessity for flexible shafts used in conventional drive mechanisms as means for converting rotational motion to linear motion, thus providing compact design, smoother operation and enhanced accuracy in determining detector position. (Owens, K.J.)