Abstract: A water-cooled nuclear reactor pressure vessel is internally provided with a check valve assembly for the inner end of a coolant inlet nozzle to prevent immediate loss of the coolant from the vessel by backward flow in the event the pressure of the coolant supply through the nozzle, drops below the pressure inside the vessel while the reactor is operating. The valve assembly includes a plurality of flap valves working in parallel so that if one fails to close when required, the balance of the flap valves remain operative to check the discharge of the coolant.

Abstract: A pressurized-water reactor installation comprises a pressure vessel containing a core, a main reactor coolant system formed by one or more main coolant loops which are each formed by a steam generator and a main coolant pump and main coolant piping interconnecting the vessel, pump and generator. A pressurizer is connected with the coolant system to maintain a normal operating pressure on water in the loop and which prevents the water from boiling in the loop and pressure vessel. An emergency core cooling system is provided which includes a supply of emergency water and activating means responsive to a drop in the normal operating pressure in the loop, for automatically feeding the emergency water into the vessel to flood the core. In case the pump fails to operate, the pressure in the loop increases due to overheating of the water.

Abstract: A pressurized-water reactor coolant system has a main coolant pipe connecting with the reactor pressure vessel through a check valve. A tubular containment is fixed to the pressure vessel and extends over the check valve and connects with the pipe beyond the check valve.

Abstract: A pressurized-water reactor pressure vessel has a plurality of inlet openings through which coolant is introduced from the cold legs of a plurality of main coolant loops, into an annular descent space of restricted radial extent and formed between the inside of the vessel's side wall and the outside of a core barrel on the inside of the vessel. To prevent outward loss of coolant from the vessel in the event of a break in any of the cold legs, the vessel is internally provided with a check valve assembly for each of the inlet openings, and to avoid restriction of the normal inlet coolant flow rate, each assembly comprises a plurality or series of flap valves which are each individually of small dimensions so that they can be fitted into the descent space. Therefore, these flap valves are normally held open by the inlet coolant flow but can snap shut to outward coolant flow.

Abstract: A boiling-water reactor has control rods operable from the top of the reactor pressure vessel and has control rod guide tubes structurally connected with upwardly removable water separators in a steam space above the reactor core.

Abstract: Coolant fluid within the nuclear reactor is fed under pressure to the lower end of the guide tubes. Control rods are disposed within the guide tubes and are movable hydraulically by means of the pressure transmitted from the lower end of the guide tubes. This pressure supports the control rods and tends to move them up, out of the guide tubes and out of the adjacent core. As a result of this arrangement, in event of malfunction or accident causing a loss of pressure, the control rods are not withdrawn from the guide tubes but, instead, are further inserted into the guide tubes and into the core.