GB1478985A - Nuclear reactor fuel element sub-assemblies - Google Patents

Abstract

1478985 Fuel elements UNITED KING- DOM ATOMIC ENERGY AUTHORITY 24 March 1975 [1 Feb 1974] 04869/74 Heading G6C A nuclear reactor fuel element sub-assembly comprises a bundle of spaced parallel fuel pins within a tubular wrapper, the pins having peripherally enlarged heads at one end and the heads being captive between a fixed end abutment grid and a fixed cellular grid, the one end of each pin being formed with coolant flow passages. An embodiment of such a sub-assembly, for use in a fast reactor, is shown in Fig. 2 and comprises upper and lower grids 5, (6) secured to the wrapper, one at each end of the bundle of fuel pins, and each comprising a series of parallel spaced bars 7, the fuel pins 1 being spaced apart by a series of spaced cellular grids 8. Coolant flow is upwardly along the bundle of fuel pins. The fuel pins have peripherally enlarged heads 9 at their upper ends and the heads are captive between the upper grid 5, which forms an end abutment grid, and a cellular support grid 10 secured in fixed relationship to the wrapper and the uppermost pin spacing grid 8. The end portions of the fuel pins 1 are necked to form shanks 11 intermediate the heads 9 and the necking 12. As seen in Fig. 3, the cell-defining elements 13 of the grid 10 each have six concyclic promontories 14 for radial abutment with the shanks 11. A circumferential series of grooves 15 extends along the shanks 11 and the heads 9 to provide coolant flow passages for reducing the pressure drop and consequent cavitation caused by the restriction to coolant flow of the cellular support grid 10. In a second embodiment (Figs. 4 and 5, not shown), the upper end portion of each fuel pin has a counterbore extending from the enlarged head and coolant flow passages are formed by a circumferential series of closed end slits, the slits extending longitudinally along the end portion of each pin to the head and through the wall of the counterbore. In a third embodiment (not shown), the upstanding fuel pins have lower ends formed in a manner identical to the upper ends of the fuel pins of the first embodiment and the pins are supported by a lower support grid. A cellular grid identical to the cellular support grid of the first embodiment is provided to hold captive the enlarged heads of the fuel pins and prevent substantial levitation of the fuel pins.