GB1130633A - Fuel assemblies for nuclear reactors - Google Patents

Abstract

1,130,633. Fuel elements. ENGLISH ELECTRIC CO. Ltd. 23 Aug., 1966 [24 Aug., 1965], No. 36408/65. Heading G6C. A fuel element assembly comprises an annular space through which coolant may flow over fuel bins situated in the space and a central channel through which a control-rod may move. The control-rod may be lowered to the bottom of the channel and coupled to the assembly at its lower end whereby the rod and fuel element assembly may be removed as a unit from the reactor by a lifting force applied to the top end of the control-rod. As shown, a gascooled graphite-moderated reactor has its pile cap (10), (Fig. 1, not shown), penetrated by a plurality of standpipes (11) closed by a plug (12), each standpipe having an extension 13 reaching down to a fuel channel 20 in a core formed by a top neutron shield 14 and moderator 15. Each fuel assembly comprises coaxial outer and inner stacks 30 and 31, respectively, of cylindrical graphite sleeves 30A ... 30C, 31A ... 31C, the bottom of the assembly consisting of a central boss 33 connected by a grid 35 to an outer ring 34. The conical surface of the ring 34 is supported by a seating 23D of a gag valve housing 23 fixed by a flange 23A to the core support plate 16. The grid 35 supports the lower ends of the fuel bins 36 spaced along their lengths by grids 38. The gag valve controls the flow of coolant gas from the inlet plenum 17 to the lower end of the annular space between the stacks 30, 31 and includes ports 23B in the housing 23 and ports 25A in a rotatable cylindrical valve member 25. The valve member 25 is rotated to control the gas flow by means of teeth 25C co-operating with teeth 37A on a member 37 secured to the boss 33, the arrangement being such that each time the member 37 is moved axially away from the valve member 25 and then back again it rotates the valve member by one tooth pitch. This axial movement is derived by lifting a control rod 55 supported by a chain 54 in the fuel assembly, the lower end of the control rod being formed with the male part (55B) (Fig. 1, not shown) of a bayonet fitting co-operating with a female part 60. A stem 61 extends from the part 60 to a lifting head 62 whereby after the control-rod 55 has been lowered by the chain 54 to the end of its channel and then rotated to engage the bayonet connection the fuel assembly may be either raised a small amount and then lowered to rotate the valve member 25 or it may be raised to engage the bottom of the plug (12) and the plug together with the fuel assembly then removed from the reactor. The winding mechanism (53) for the chain 54 is situated in the plug. The upper end of the fuel assembly is formed by a neutron shield plug 41 formed with helical gas passages 42.