Patent Number: 043228534
Section: claims

1. In a nuclear reactor incorporating a plurality of columns of tubular fuel elements disposed in horizontal tubes in a mass of graphite wherein water flows through the tubes to cool the fuel elements, the improvement comprising at least one control column disposed in a horizontal tube including fewer fuel elements than in a normal column of fuel elements and tubular control elements disposed at both ends of said control column, and means for varying the horizontal displacement of the control column comprising a winch at the upstream end of the control column and a cable extending through the fuel and control elements and attached to the element at the downstream end of the column. 2. The improvement of claim 1 wherein the number of fuel elements in the control column is approximately one-half the number in a normal fuel column and the number of poison elements is sufficient so that the control column is longer than a normal fuel column. 3. The improvement according to claim 2 and including means for limiting the movement of the control column. 4. The improvement according to claim 3 wherein said means for limiting the movement of the control column includes a micropotentiometer having a shaft locked to the shaft of the winch, a housing having a resistance wire integral therewith, a wiper arm which is attached to the shaft of the micropotentiometer and which traverses the resistance wire, stops on said resistance wire which limit the movement of the wiper arm, a bar connected to the center of the end of the housing, a pair of springs engaging opposite sides of the bar, and limit switches which are operated by said bar when said springs are depressed.