Diving bell type control rod equipped with sodium inflow port

A diving bell type control rod having a control element including

• a cladding tube to be immersed longitudinally in a liquid sodium coolant, both ends of said cladding tube being provided with upper and lower end plugs;
• a pellet chamber disposed in said cladding tube for loading a plurality of pellets of boron carbide;
• an intermediate plug disposed above said pellet chamber;
• an upper chamber formed above said intermediate plug;
• a vent tube so disposed as to penetrate through said intermediate plug and to allow said pellet chamber to communicate with said upper chamber;
• and
• a vent hole so formed as to penetrate through said cladding tube located at said upper chamber;
• characterized in that
• said vent hole comprises an upper vent hole and a lower vent hole formed in upper and lower two stages in such a manner as to penetrate through said cladding tube located at said upper chamber,
• a sodium inflow port is so formed as to open to the upper surface of said intermediate plug, and
• a sodium introduction tube is so disposed as to extend from said sodium inflow port to a position below the lower end surface of said vent tube while penetrating through said intermediate plug.