Passive activation safety device for nuclear reactor on abnormal dropping in primary flow

The present invention relates to a manual actuation safety device for a nuclear reactor. The manual actuation safety device includes: a sleeve unit (200) which has a coolant passing there-through in a vertical direction (3) and is extended in the substantially vertical direction (3) in an operation; and a movable cartridge unit (100) which is movably installed in the sleeve unit (200) in the vertical direction (3). The movable cartridge unit (100) includes a first support unit (110) spaced apart from a neutron absorber in the vertical direction (3). The sleeve unit (200) includes a second support unit (210). The first and second support units (110,210) are arranged to face each other. When the flow amount of the coolant passing through the sleeve unit (200) in the vertical direction (3) (Qf) is higher an operation flow amount (Q), the coolant lifts the movable cartridge unit (100) in the sleeve unit (200) while applying a force sufficient for maintaining the lifting arrangement to the movable cartridge unit (