| 摘要 |
1,139,969. Fuel elements. COMMISSARIAT A L'ENERGIE ATOMIQUE. 27 Nov., 1967 [5 Dec., 1966], No. 53773/67. Heading G6C. A nuclear fuel assembly comprises at least one bundle of fuel pins provided with expansion chambers and disposed in a coolant circulation duct, a tubular support located along the axis of the duct, and top and bottom end fittings respectively connecting the upper and lower ends of the duct and support, the latter supporting the fuel pins and defining an axial passageway which by-passes the space between the expansion chambers. The assembly for use in a fast reactor, shown in Figs. 1 and 2, comprises a central bundle 10 of pins loaded with fissile material disposed between a top bundle 12 and a bottom bundle 14 of pins loaded either with fertile material or with neutron-absorbing material. A tube 16 is secured at its lower end to a bottom end fitting 18 provided with coolant inlets 20 and an annular plate 22 is secured around the top of the tube 16. The pins of the central bundle 10 are of smaller diameter than those of the top and bottom bundles 12, 14 and are supported on rails secured to a grid 35. In order to permit of their free expansion, the upper ends of these pins are simply guided by another set of rails secured to a grid 34. The grids 34, 35 are provided with openings for the flow of coolant and are secured to the tube 16. The lower half of each fuel pin constitutes an expansion chamber and is separated from the upper fuel-containing half by a neck 36. A thin-walled sleeve 38 which may be formed from a spirally - wound strip surrounds the three bundles 10, 12, 14 and is attached to the bottom end fitting 18 and to the annular plate 22. At the level of the necks 36, the tube 16 contains a series of coolant outlets 44, and immediately above this level it is sealed off by a plug 42. Coolant is admitted through the inlets 20 and the greater part of the flow passes upwardly through the tube 16 and is discharged through the outlets 44, thus by-passing the bottom bundle 14 and that portion of the central bundle 10 comprising the expansion chambers. A fraction of the flow passes out of the duct 16 through ports 46 and enters the bottom bundle 14, cooling the pins of this bundle and the expansion chambers of the pins of the central bundle 10. A collector space 37 formed by the necks 36 permits uniform cooling of the fuelcontaining portion of the bundle 10. The total flow cools this portion and the top bundle 12 before passing out through openings 48 in the annular plate 22. |
