GB1063696A - Nuclear reactor - Google Patents

Abstract

1,063,696. Reactors. U.K. ATOMIC ENERGY AUTHORITY. Oct. 16, 1964 [Oct. 28, 1963], No. 42408/63. Heading G6C. An integral nuclear reactor has a reactor vessel 21 housing a reactor core 11 above which is an annular heat exchange plenum 41 containing a plurality of U-shaped tubular heatexchange elements 54 connected in parallel between inlet and outlet headers 55 (only one of which is shown in section), the headers 55 comprising straight ducts which project outwardly through the reactor vessel 21 to plugged access ports 56 at their outer ends, a branch duct 58 being connected to each header 55 outside the reactor vessel 21 for connection of that header into a heat utilization circuit. The core 11, incorporating fuel elements 12 located between top and bottom apertured grids 13, 14 is supported by top and bottom support plates 15, 16, shrouds 17 between the plates 15, 16 serving both as a thermal shield and as a coolant baffle. A bottom thermal shield 18 below the core 11 defines a coolant inlet plenum 19. The gap between the reactor vessel 21 and the shrouds 17 is divided by a conical baffle 22 into a pump inlet plenum 23 and a pump outlet plenum 24. Three primary coolant pumps 25 (of which two are shown), are spaced around the reactor vessel 21, being supported by coaxial ducting 26 connecting them to the plenums 23, 24 and steadied at their upper ends by brackets 27 projecting from the reactor vessel 21. In operation, primary coolant water enters the plenum 23 through apertures 28 in the top core support plate 15, is pumped into the plenum 24 and then flows through the inlet plenum 19 into the core 11. The heated coolant leaves the core 11 by flowing upwardly through the top grid 13. Above the core 11, a control mechanism plenum 31 is defined by a housing 32 within which transverse grids 33 support control mechanisms in the form of scram rod mechanisms 34 and regulating rod mechanisms 35. In order to reduce the cross-sectional area of the upper end of the reactor vessel 21, and therefore to reduce the force exerted by internal pressure in a direction to blow-off the lid 38, the reactor vessel is formed with an internal flange 44. The flange 44 and the lid 38 define an internal steam dome 51 for self-pressurization of the reactor primary coolant. The upper end of a baffle 39 closely surrounding the housing 32 is - secured to the flange 44 but is provided with apertures 52 for the flow of primary coolant into the heat exchange plenum 41. Within the steam dome 51 the coolant forms a free surface 53 at which evaporation takes place to build up a steam pressure in the dome which is imposed upon the coolant being circulated through the core and is augmented in the core by the pressure developed by the primary coolant pumps. The plenum 41 houses a plurality of separately removable heat exchange units, each comprising two headers 55 between which a plurality of tubular elements 54 are connected in parallel. The headers 55 have branch ducts 58 through which the secondary coolant flows to and from the tubular elements 54, which ducts are each provided with an isolating valve 60. If a tubular element 54 develops a fault, such as a leak, the element is isolated by plugging it at each end by means of plugging devices inserted into the corresponding headers 55 through the ports 56 after the closing of the corresponding isolating valves 60 and the removal of the plugs 57 from the ports 56. Such maintenance may be carried out without elaborate servicing apparatus and the invention, therefore, is of particular advantage in the field of marine propulsion.