Patent Number: 
Section: claims

1. In a pressurized water nuclear reactor, a reactor pressure vessel for containing fuel assemblies in coolant water, comprising:a removable top head having a flange with a bottom surface;a vessel body having an internal support ledge;a core barrel assembly having a flange supported on the internal support ledge for supporting the filet assemblies, the core barrel assembly flange having holes extending between a lower flange surface and an upper flange surface, each hole having a cross-sectional area; andan upper support plate having a flange with a lower flange surface and an upper flange surface, the lower surface of the upper support plate flange disposed above the upper surface of the core barrel assembly flange, the upper support plate flange having holes extending between its lower surface and its upper surface and aligned with the holes in the bore barrel assembly, the upper support plate having exhaust nozzles extending from the holes and above its upper surface, each exhaust nozzle having an exit port having an exit flow area that is larger than the cross-sectional area of the aligned hole in the core barrel assembly, and each exit port is disposed above the bottom surface of the top head flange. 2. The reactor pressure vessel of claim 1, wherein the exhaust nozzles are sized to reduce the coolant water flow velocity to 25% of the coolant water flow velocity through the aligned holes in the core barrel assembly flange. 3. In a reactor pressure vessel for containing nuclear fuel assemblies in coolant water, comprising:a vessel body having an internal support ledge;a removable top head having a flange with a bottom surface adjacent the vessel body flange and having an inner surface defining a head cavity;a core barrel assembly having a flange supported on the internal support ledge for supporting the fuel assemblies, the core barrel assembly flange having a plurality of holes extending between a lower flange surface and an upper flange surface; andan upper support plate having a flange with a plurality of holes extending between a lower flange surface and an upper flange surface, the lower surface of the upper support plate flange disposed above and spaced from the upper surface of the core barrel assembly flange, the lower surface of the upper support plate flange and the upper surface of the core barrel assembly flange defining an inter-flange cavity, with the holes in the upper support plate flange aligned with the holes in the core barrel assembly flange, and the upper support plate flange having a periphery extending between its lower flange surface and its upper flange surface;a method of diverting a flow of coolant water into the top head, comprising the steps of:providing exhaust nozzles in the holes in the upper support plate flange that extend to exhaust nozzle exit ports disposed in the top head cavity and having larger exit port cross-sectional areas than the cross-sectional areas of the aligned core barrel assembly flange holes; and thencontrolling the flow of coolant water into the head cavity from the inter-flange cavity while controlling leakage of coolant water from the head cavity around the periphery of the upper support plate flange into the inter-flange cavity. 4. The method of claim 3, wherein the step of providing exhaust nozzles comprises: providing exhaust nozzles sized to reduce the coolant water flow velocity to 25% of the coolant water flow through the aligned holes in the core barrel assembly flange. 5. The method of claim 3, wherein the step of controlling the flow of coolant water comprises: controlling entrainment of coolant water leaking around the periphery of the upper support plate flange by the flowing coolant water.