Patent Number: 039792587
Section: description

In the reactor illustrated in FIG. 1, a control rod 3 is fixed to a double-acting piston 2 which works in a cylinder 1. Hydraulic or pneumatic fluid applied in the cylinder at the side of the piston 2 remote from the control rod 3 drives the rod 3 into a bulk charge of spherical reaction elements 4, the rod forcing a path between the elements. The rod 3 is retracted by reversing the hydraulic or pneumatic fluid supply to the cylinder 2. The external surface of the rod 3 has a number of helical screw threads along its length, the threads on the lower or leading part 7 of the rod having a greater pitch than the threads on the upper part 6. The axial extent of the leading part 7 is preferably limited to the ratio of 360.degree. to the number of threads. When the control rod 3 is being thrust into the bulk charge of spherical reaction elements it rotates, either to the right or to the left, depending on the direction of the threads, and the spherical reaction elements 4 are thrust aside by the screw threads. Due to the rotation of the rod the thread of greater pitch on the leading part 7 of the rod applies a lifting thrust to the spherical reaction elements engaged by it and this makes it easier for any element which happens to be directly in line with the axis of the rod to escape sideways. Consequently the spherical reaction elements are not greatly stressed mechanically and no major bending stresses are applied to the control rod. In this regard the reactor in accordance with the invention has the particular advantage, compared with conventional reactors of a similar type, that during the movements of the rods the reaction elements are not compacted and are retained sufficiently loose to prevent them from suffering damage due to excessive mechanical stressing. Friction between the reaction elements is considerably reduced by choosing a suitable cross section for the threads on the control rods. For example the threads may be a modified round thread as shown in FIG. 2. FIGS. 3 to 6 illustrate two further examples in accordance with the invention. In both cases the control rods are guided and driven as already described above for FIG. 1. The differences between these further examples and that of FIGS. 1 and 2 lies in that the threads on the lower end part 7 of each rod are replaced by means which is equivalent to threads of infinite pitch, the threads on the upper part 6 remaining the same. In the example shown in FIGS. 3 and 4, the lower end part 7 of the rod 3 has ribs 8 projecting outwards from the surface of the rod and extending parallel to the longitudinal axis of the rod. The ribs 8 may be formed integrally from the material of the rod or if desired they may be in the form of strips welded to the lower part 7 of the rod. In the example shown in FIGS. 5 and 6 the lower end part 7 of the rod is elliptical in cross section (FIG. 6), the difference between the two axes of the ellipse having a similar effect to the ribs 8 of the example shown in FIGS. 3 and 4 in that when the rod is penetrating between the spherical reaction elements the lower end part 7 is effective in displacing the spherical reaction elements and loosening up the bulk charge when the rod is rotated by the engagement of the threads 6 and the charge. Instead of an elliptical cross section the lower end part 7 of the rod may if desired have a polygonal cross section.