Abstract: A liquid absorbent safety device for a nuclear reactor, constituted by a cylindrical tank comprising two communicating superposed compartments. The upper compartment situated above the reactor is filled with liquid absorbent surmounted by a gas under pressure. The lower compartment situated in the core is filled with gas under pressure and is provided with a connection to the outside terminated by a closing member sensitive to the operating conditions of the reactor. If the reactor begins to malfunction, the closing member is destroyed thereby causing depressurization of the lower compartment and the precipitation of the liquid absorbent into the lower compartment.