GB1013920A - Improvements in or relating to fuel elements for nuclear reactors - Google Patents

Abstract

1,013,920. Fuel elements. COMMISSARIAT A L'ENERGIE ATOMIQUE. Aug. 28, 1963 [Aug. 31, 1962]. No. 34049/63. Heading G6C. A tubular, internally and externally sheathed nuclear fuel element which is used as one of a string of similar fuel elements has the internal sheath 42 provided with helical fins 44, the arms 47a, 47b . . . of a lightweight spider member 47 being seated within longitudinal channels 45a, 45b . . . traversing the fins 44 and defining sectors 48 for the internal circulation of cooling fluid, suitable deflecting means being provided at the ends of the fuel element so that the cooling fluid flowing internally of this element flows externally of the subsequent element, and vice versa. Preferably, the external sheath 43 is provided with fins 49, 50, inclined in opposite directions forming a longitudinal herring-bone pattern. The element is positioned at the centre of a channel 51 in a moderator 52 by positioning members 53 which divide up the circulation of the external fluid into sectors 54, in each of which the fluid is split into two helical circulations in opposite directions, as is indicated by the arrows 55, 56. The helical fins 44 all run in the same direction, as is indicated by the arrows 46 showing the direction of circulation of the internal fluid. The deflecting means at the ends of each element cause the internal and external fluid flows to be exchanged between adjacent elements as indicated by arrows 57, 58. This entails the internal sectors 48 and the external sectors 54 being provided in equal numbers, but staggered so that the currents of an external fluid flow tangentially encounter those of the corresponding internal fluid flow and vice versa. The spider member 47 may be extended to the wall of the channel 51 at the ends of the element so as to help position and support the element and may be oriented and curved at its ends so as to form the deflecting means. Alternatively, the deflecting means may be provided by members fixed to the ends of the positioning members 53. In an alternative embodiment (Fig. 2, not shown), the external sheath is provided with longitudinal fins, some of which are taller than the others and assist in the positioning of the element at the centre of the moderator channel, and the helical fins on the internal sheath run in opposite directions in adjacent sectors.