GB991004A - Self-adjusting neutron absorber for the control of nuclear reactors - Google Patents

Abstract

991,004. Temperature responsive actuating elements. AGIP NUCLEARE S.p.A. Nov. 27, 1961 [Nov. 29, 1960], No. 42284/61. Heading G1D. [Also in Division G6] A self-adjusting neutron absorber for controlling distortion and instability in the neutron flux distribution in a nuclear reactor comprises mobile and fixed neutron-absorbing surfaces, and elements connected directly to the mobile surfaces responsive to variations in the temperature of the coolant gas or variations in the neutron flux in the reactor such that these variations cause the elements to move the mobile surfaces relative to the fixed surfaces resulting in corresponding variations in the area of neutron-absorbing surface in the absorber. In one embodiment (Fig. 1), the mobile and fixed surfaces comprise the series 1, 2 of circular sectors of strongly neutron-absorbing material, e.g. boron steel or cadmium, the series 1 being fixed to a shaft 3 and the series 2 to the internal walls of a cylindrical container 4. The shaft 3, which is pivotally mounted between shock absorbers 14, 15 is connected to the central ends of a system 8 of three bimetallic laminae wound in spirals, the outer ends being secured to the container 4. Variations in the temperature of the coolant gas which enters through bores 6 and leaves through bores 7 cause the system 8 to rotate the shaft 3, maximum neutron absorption occurring when the series 1 is midway between the series 2 and minimum when the two series overlap. Where the absorber is sensitive to the neutron flux, one of the metals of the bimetallic laminae contains a fissile material, variations in the neutron flux causing variations in the energy developed by fission and hence in the temperature of the laminae. In a modification (Fig. 2, not shown), the variation in absorbing surface area takes place by relative rotary motion between a fixed series of cylindrical segments and a mobile series. In an alternative embodiment (Fig. 3), the variation of neutron absorption is effected by the relative translatery displacement of two coaxial tubes 1, 2 of strongly neutron-absorbing material. The tube 1 is guided by a shaft 5, supported by springed shock-absorbers 6, 7, along which it can slide. A system 8 of bimetallic spun discs 9, superposed and linked by means of rings 10, 11 (Fig. 3c), transforms temperature variations of the gas entering the absorber through bores 12 and leaving through bores 13 into longitudinal displacements of the tube 1.