Latch assembly for a control rod drive

This patent describes a control rod drive for positioning a control rod in a nuclear reactor vessel. It comprises: a shaft; a ballnut positioned over the shaft and being translatable upon rotation of the shaft; a piston disposed coaxially with the shaft and on the ballnut for positioning the control rod; means for selectively rotating the shaft in a first direction and in a second direction, opposite to the first direction; a housing surrounding a portion of the shaft; a gear fixedly joined to the shaft, the gear having a plurality of circumferentially spaced gear teeth; a latch arm pivotally joined to the housing, and having at least one latch tooth facing the gear teeth; and means for selectively positioning the latch arm in an engaged position to abut the latch tooth against a first one of first direction, and in a disengaged position to spaced the latch tooth away from the gear teeth for allowing the shaft to rotate without obstruction between the gear teeth and latch tooth for translating the ballnut and in turn the piston for inserting and withdrawing the control rod in the reactor vessel