LIQUID LITHIUM CONTROL TYPE FAST BREEDER

PURPOSE:To achieve a simplification of a construction dispensing with a rotary plug by arranging a control body having an expandable closed cylinder body within a case parallel to a reactor core shaft in an outer circumferential area of a reactor core to connect a tank of liquid lithium to the closed cylinder body. CONSTITUTION:To control an output of a nuclear reactor, a pump 22 of a controller 13 is started to suck a coolant within a reactor vessel 2 from a piping 16 to flow into a lower space 23 in a case 17 through a piping 15. As a result, a pressure in the space 23 rises higher than that in a closed cylinder body 20 to compress a bellows joint 19 of the cylinder body 20 so that the cylinder body 20 is reduced in an axial direction thereof to achieve a balance between the pressure inside and outside the cylinder body. With the reduction of the cylinder body, a part of a liquid lithium 25 inside is extruded to be returned to a tank 21. A lower end of a liquid column of the liquid lithium 25 in the case 17 rises accordingly, a condition which is as noted when a control rod is pulled out in the reactor. When the pump 22 is stopped to open a valve 24, the cylinder body 20 stretches by a return force of the joint 19 of the cylinder body 20 and the coolant is extruded to be returned into the reactor vessel through the piping 15 or the like.