Control rods for HTGR type reactors

Purpose: To moderate the thermal stresses resulted to cladding tubes in HTGR type reactors even when control rods are rapidly inserted into the reactor core upon emergency. Constitution: A control rod is prepared by successively connecting a plurality of double cylindrical control rod elements to a spine having a plurality of spiders disposed by means of stoppers secured substantially at an equal distance to the spine. Heat shielding members are disposed so as to surround the connecting portions between each of the control rod elements. Since the amount of heat radiation to the cladding tube is reduced and direct entrance of heat due to radiation to the upper and lower ends of the cladding tube undergoing severe stresses is prevented, no abrupt temperature slope is resulted and less thermal stresses are generated. Accordingly, the thermal stresses exerted upon rapid insertion of the control rod can significantly be moderated to extend the control rod life. No undesired problems due to high temperature and thermal stresses are resulted in view of the structure of the heat shielding plates which are formed at a reduced thickness and made of heat resistant material with small heat radiation rate. (Kawakami, Y.)