Control rod

Purpose: To enable to attain stabilized buffering performance upon control rod drop irrespective of conditions such as the reactor core temperature and the height of the dropping position. Constitution: Molded bellows buffers having different rigidities are arranged serially to the lower end of a control rod element to be vertically moved within the reactor core along the axial direction of a control rod main body. In the case where the control rod main body drops under a high temperature atmosphere during power operation, that is, where the yielding stress of the bellows is reduced and thus the energy absorbing performance is reduced, or in the case where the control rod main body drops from a higher position even under a low temperature atmosphere, the first bellows is at first yielded to deform plastically and, thereafter, the secondary bellows with a higher rigidity also deforms plastically to absorb dropping energy. (Kawakami, Y.)