Patent GB-1057777-A (GB)
Title: Pulsed or modulated nuclear reactors
IPC: G21C1/30
Filed: 1964-04-23
Abstract: 1,057,777. Reactors. SIEMENS-SCHUCKERTWERKE A.G. April 23, 1964 [April 24, 1963], No. 16964/64. Heading G6C. A pulsed or modulated nuclear reactor comprises means for moving one or two control masses of neutron-producing (e.g. fissile), neutron-reflecting or neutron-absorbing material outside of and relative to the reactor core so that the control mass(es) never enter(s) the core, the arrangement being such that in operation the reactor is pulsed or modulated by virtue of such movement of the control mass(es). In one embodiment (Fig. 2, not shown), a pulsed fast reactor is constructed from fuel rods 1, 2 and 3 of differing lengths so as to provide a core of substantially spherical form. The fuel rods, which contain highly enriched nuclear fuel, are surrounded by reflector rods 9 and housed in a container 10 through which a Na-K liquid coolant flows. An outer reflector 50 surrounds the container 10 except for one side of the core, the fuel rods 2 adjacent which side are longer than the corresponding fuel rods 3 adjacent the other sides of the core. On this side of the core also, the reflector rods 9 are replaced by fuel rods 2 so that a reactor window is formed. Extending through the reflector 50 at suitable points are radiation tubes 60, 61 for measuring and testing purposes. The arrangement for pulsing the reactor comprises a housing 11 in which are disposed two rotating discs 12, 13 whose axes 6, 8 extend parallel to the window axis 4. Shafts 14, 15 of the two discs 12, 13 are driven in opposite directions by electric motors 16, 17. Both discs 12, 13 support at one point of their periphery reflector pieces 5, 7 respectively, consisting of non- fissile material, the first of which, contributing the greater amount of reactivity, determines the pulse shape, while the latter determines the frequency. In the present case of a pulsed fast reactor, steel, titanium, magnesium, aluminium and their alloys may be employed for the discs 12, 13 while the reflector pieces 5, 7 may consist of beryllium, molybdenum, nickel or steel. Beryllium or graphite could be used for the reflector pieces 5, 7 in the case of a thermal reactor. In the embodiment described, the main disc 12 has a constant speed of rotation of 6000 r.p.m. while that of the frequency selector disc 13 may be adjusted in four stages to 750, 1500, 3000 and 6000 r.p.m. (ratios of 8: 1, 4: 1, 2: 1 and 1: 1). In operation, a reactor power pulse is consequent upon a momentary alignment of the two reflector pieces 5, 7 with the reactor window, the discs 12, 13 being rotated in opposite directions. In alternative arrangements, the two control masses may share the aperture of the reactor window or two sides of the reactor core may be constructed as windows and each be provided with a control mass. In the case of a modulated reactor, a single rotating disc is disposed in front of the reactor window and in one embodiment (Fig. 4a, not shown) such a disc 34 is formed in an annular peripheral zone with bores 44 into which reflector pins 45 of hexagonal cross-section can be so introduced that a number of reflector regions of any geometrical form can be produced in alternating sequence around the disc. The reflecting material used for the pins 45 may be the same as that used for the reflector pieces 5, 7 of the first embodiment. The centre points of the bores 44 are the points of intersection of concentric circles around the axis of rotation of the disc 34 with radial rays and in order that the reflecting surfaces may be filled as compactly as possible, the pins 45 are of increasing cross-section towards the perimeter of the disc 34.