Nuclear reactor installation with a core catcher device and method for exterior cooling of the latter by natural circulation

A method for starting and maintaining exterior cooling of a core catcher device of a nuclear reactor installation having:

• a reactor pressure vessel, a reactor core in the reactor pressure vessel, a primary circuit having main coolant lines leading to the reactor pressure vessel, pressure reservoirs communicating with the main coolant lines;
• a supporting and protective structure supporting the reactor pressure vessel and surrounding the reactor pressure vessel on the bottom and laterally, the supporting and protective structure having a bottom region and a circumferential wall;
• a core catcher device for the reactor core having a collecting basin for a core melt being installed below the reactor pressure vessel, the collecting basin having a bottom wall and a jacket wall being respectively separated from the bottom region and the circumferential wall of the supporting and protective structure by a spacing gap;
• a collecting basin cooling system having cooling channels disposed in the spacing gap at the bottom wall and the jacket wall for exterior cooling of the collecting basin with a cooling liquid;
• turbulence bodies disposed in a surface region of the bottom wall for generating a turbulent flow of the cooling liquid flowing from the inside to the outside over the bottom wall toward the jacket wall;
• and a cooling water reservoir disposed outside the supporting and protective structure, an inlet channel configuration connecting the cooling channels at the bottom wall to the cooling water reservoir and an outlet channel configuration connecting the cooling channels at the jacket wall to the cooling water reservoir, with a lift generating a naturally circulating flow through the cooling channels when the collecting basin is hot and the cooling channels are filled with water;
• the method which comprises:
• maintaining a cooling water level of the cooling water reservoir at a low water level, during normal operation of the nuclear reactor installation, at which no cooling water can reach the inlet channel configuration of the collecting basin cooling system,
• feeding emergency cooling water, when a leak occurs in the primary circuit, from the pressure reservoirs to be activated as a function of pressure of the primary circuit into the main coolant lines of the reactor pressure vessel, by feeding the emergency cooling water through the leak location and, if necessary, parallel thereto through further feed locations into the cooling water reservoir, and
• maintaining a sufficient water volume in the pressure reservoirs to lift the cooling water level of the cooling water reservoir up to a high water level for causing cooling water from the cooling water reservoir to reach the inlet channel configuration and from there the spacing gap of the collecting basin cooling system for filling the cooling system up to the level of the outlet channel configuration, for starting a naturally circulating flow, when the collecting basin is hot, from the cooling water reservoir through the inlet channel configuration to the cooling channels at the bottom wall and the jacket wall of the cooling system and from there through the outlet channel configuration back to the cooling water reservoir.