| 摘要 |
920,256. Nuclear reactors. COMMISSARIAT A L'ENERGIE ATOMIQUE. June 3, 1959 [June 5, 1958], No. 19015/59. Class 39 (4). A fuel element for a nuclear reactor comprising fissile material enclosed in a can is characterized in that the cross-sectional perimeter of the can varies, in a continuous or discontinuous manner, along its length in such a manner that the temperature of the can is near the maximum allowable value at all points during operation of the reactor. In Fig. 1, a cylindrical bar 3 of fissile material is enclosed in a cylindrical can provided with radial fins 5, the radial extension of which varies along the length in accordance with a mathematical formula given in the Specification. Two of the pins have a constant radial extension and serve to locate the element in the fuel channel. The fins are thin so the cross-sectional area available for coolant flow is practically constant along the length of the fuel element. Another type of element is shown in cross-section in Fig. 6; the shaded areas a, b are equal so that the crosssectional area of the fuel element, and therefore of the coolant path, is constant along its length whilst the perimeter varies as before. In a modification of this type, Figs. 7 and 8 (not shown), the element is hollow and comprises two cans, of clover-leaf cross-section, with fissile material between them, the thickness of the fissile material varying so that the fissile material is equally distributed along the length of the element. In Fig. 9 the fuel element comprises a number of flat sub-elements arranged in groups which are at right angles to adjacent groups. The number of sub-elements are 3, 4, 5, 6, 5, 4 in the direction of coolant flow; thus the cross-sectional perimeter varies discontinuously and may be equal to the desired theoretical value at the centre of each group. Fig. 10 shows another type of element formed of sub-elements; each sub-element tapers uniformly from a maximum diameter at about two-thirds the way along its length to smaller diameters at each end. In Fig. 11, the fuel element comprises a number of cylindrical subelements, the diameters of which vary so that the perimeters follow approximately the required law; in a modification, Fig. 12 (not shown), the sub-elements are frusto-conical, so that the outer surface of the element as a whole is smooth. The elements may be provided with radial fins to support them in the cooling channel. |
