Abstract: Steam generators are used in pressurized water-cooled nuclear reactors for generating steam which issues from the generator through a large bore steam outlet. Heat-exchange tubes through which feed water flows are surrounded by hot cooling water from the reactor. The tubes must be capable of being inspected and repaired. To simplify inspection and repair, the tubes are U-shaped and each end of each tube is connected upwardly to a tube plate in the steam generator, whereby each end of each tube can be reached in a simple manner through an outgoing steam outlet.

Abstract: A heat-generating member (4) is arranged in a water-filled pressure vessel (1) which is provided with a pressure relief valve or the like. The water of the pressure vessel can be partly evaporated, thereby acting as a heat sink for the generated heat. The walls of an outer vessel (6) surround at least a lower part of the pressure vessel (1) in such a way that a closed, relatively small auxiliary space (7) is formed between the two vessels. The auxiliary space (7) communicates via at least one tube (8) with an open evaporation pool (9), which is arranged above the cover (2) of the pressure vessel (1). A tube coil (10), disposed in an upper part of the pressure vessel, is connected by both ends to the evaporation pool (9).

Abstract: A pressurized water nuclear reactor comprises a reactor vessel arranged in a pool made in the form of a pressure vessel, the pool being filled with a strongly neutron-absorbing liquid, for example borated water. The reactor vessel, in addition to being connected to a primary system, is provided with a lower shutdown opening, arranged below the reactor core, for pool liquid and with an upper shutdown opening, arranged above the core, for pool liquid.

Abstract: Boiling reactor comprising a reactor core (1) and a pressure vessel (2) enclosing said reactor core and being provided with at least one conduit for discharged steam and at least one conduit for feed water and during normal operation being filled with water up to a certain normal level (11), the steam pressure in the pressure vessel having a substantially constant value of at least 5 MPa. The pressure vessel (2) is surrounded by a water-filled pool (3) with a water volume above the reactor core (1) which is considerably greater than the water volume within the pressure vessel (2). The pressure vessel (2) is a concrete vessel having an internal thermal insulation (9). The reactor comprises emergency cooling pipes (19, 20) with valves (19', 20') connecting the reactor vessel (2) to the pool (3). The valves (19', 20') are normally closed. The pipes (19, 20) are positioned at different levels.

Abstract: A mixed oxide fuel of uranium dioxide and plutonium dioxide is in the form of mixed oxide particles with a diameter of 0.2 to 2 mm. A surface layer of the particles consists of UO.sub.2 with a plutonium content per unit of volume of at most 15 per cent of the average plutonium content per unit of volume of the particle. The particles are formed by extrusion through a concentric nozzle. A water emulsion of uranium dioxide is first pumped through the inner nozzle, after which a water emulsion of plutonium dioxide is pumped through the outer nozzle. Thereafter a water emulsion of uranium dioxide is pumped through the outer nozzle to surround the plutonium dioxide layer and then water emulsion of uranium dioxide is pumped through the first nozzle to complete the enclosure of the plutonium dioxide.