Control rod

Purpose: To moderate abrupt power changes in fuel rods at the periphery of control rods resulted upon extraction of control rods in BWR type reactors. Constitution: In a case of a cross-wise control rod comprising four blades connected with a center structure member in a cross-wise shape, the four blades are fixed by an upper fixing member and a lower fixing member. Use of the central structure member can thus be saved and the portion for the central structure member is left empty. Since the central portion in the cross-wise shape is empty, the portion is filled with moderators to moderate the neutrons satisfactorily at the center of the control rod and the difference in the power density can be made smaller between insertion and extraction of the control rod. (Ikeda, J.)