Patent Number: 
Section: claims

1. Compact pressurised water nuclear reactor, comprisinga vessel closed by a cover,a reactor core housed in the vessel,a steam generator including a base plate forming the cover of the vessel,an outer enclosure delimiting a secondary closed space with the base plate and an inverted U-shaped tube bundle located in the secondary closed space with two ends of each tube fixed to the base plate and opening in the reactor vessel,primary pumping means housed in the vessel and capable of making water circulate between the reactor core and the steam generator,and a pressuriser for pressurising water,wherein the pressuriser is housed in the reactor vessel and comprises an annular shaped reservoir with an inverted U-shaped cross-section, the top of said reservoir communicates with a tank forming a steam source, and an approximately annular partition projects downwards from the cover and delimits a peripheral region and a central region inside the vessel, the reactor core being housed in the bottom of the central region, the pressuriser being housed in the top of the central region, the pumping means being housed in the top of the peripheral region, one end of each tube opening in the central region and the other end of each tube opening in the peripheral region. 2. Compact pressurised water nuclear reactor according to claim 1, in which control mechanisms for control rods are also integrated into the reactor vessel. 3. Compact pressurised water nuclear reactor according to claim 1, in which pipe means are provided for supplying water to the said tank taken from the peripheral region, below the pumping means. 4. Compact pressurised water nuclear reactor according to claim 1, in which a venturi system, supplied with water contained in the central region, is located in the peripheral region to create a natural water circulation in this region, from top to bottom, if there is a failure of the pumping means. 5. Compact pressurised water nuclear reactor according to claim 4, in which an emergency cooling exchanger is also placed in the peripheral region below the venturi system. 6. Compact pressurised water nuclear reactor according to claim 1, in which the reactivity of the core is controlled without any soluble neutron poison in the cooling water.