CONTROLLING DEVICE OF REACTIVITY IN REACTOR

PURPOSE:To enable control of a reactor output for the situation wherein a rise in temperature is abnormal, by a method wherein an absorber for reactivity control suspended from the fore ends of movable arms is lowered by a thermal expansion difference between tension rods 7 and a rod which is a strength member. CONSTITUTION:When the temperature of a reactor coolant rises due to some cause, the fore ends of movable arms 4 are lowered with pins 6 operating as fulcrums, by a thermal expansion difference between a rod 1 and tension rods 7 of which a thermal expansion coefficient is small. Therefore a distance between pulleys 12 and 13 is made small, an absorber 14 gears with this through wires 16 and moves downward, i.e., into a core. Thereby an output of the core is limited. On the occasion, the amount of movement (amount of lowering) is set to be proportional to the distance between the pulleys 12 and 13, the number of winds of the wires 16, the rise in the temperature and the thermal expansion difference between the rod 1 and the tension rods 7 at the time of a rated operation. When the temperature of the coolant returns to the state of the rated operation, the absorber 14 made to move downward with the rise in the temperature returns to the original position automatically by a reverse operation.