[en] This patent is concerned with a particular type of feed of the emergency coolant into pressurised water reactors and into reactors with boiling water, heavy water and gas cooling. The principle lies in the direct infeed of one or more emergency coolant pipes into the pressure vessel, and particularly into the annular space between this and the nuclear containment vessel surrounding the reactor core, and in a deflection of the incoming cooling water flow downwards. This avoids a meeting with the steaming main coolant, which would otherwise worsen the emergency cooling both as regards time and economy. The deflection of the emergency cooling water when entering the pressure vessel is produced by a flow guidance arrangement set before the opening. The emergency coolant flows as a closed jet guided by the wall of the pressure vessel into the lower part of the vessel, and wets the reactor core in the direction of the continuing natural steam flow (of the steaming main cooling). The dead period before the start of the infeed of emergency coolant and the start of flooding of the core is reduced by more than half and the fuel can temperatures by 50 to 100⁰ K. (ORU)