Patent Number: 048204781
Section: abstract

A control rod for use in a nuclear reactor core to provide xenon compensation includes an elongated inner cylindrical member and an elongated outer cylindrical member surrounding the inner member. Each of the members is composed of axially-extending, alternating black poison and nonpoison regions. Also, the inner member is axially movable relative to the outer member to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod in an axially uniform manner. The inner cylindrical member has a solid cross-sectional configuration, whereas the outer cylindrical member has an annular cross-sectional configuration and concentrically surrounds the inner member. Each of the poison regions in the members is about the same axial height, while each of the nonpoison regions is about the same axial height. The guide thimble of a fuel assembly in which the control rod is placed has an annular stop being sized to support a lower end of the outer member for retaining the outer member in a stationary position therein, whereas the stop has a central hole sized to allow passage of a lower end of the inner member therethrough in order to move the inner member axially relative to the outer member to adjust the degree to which the poison regions of the members overlap with the nonpoison regions thereof and thereby change the overall worth of the rod.