GB1093029A - Improvements in or relating to nuclear reactors - Google Patents

Abstract

1,093,029. Controlling reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. June 23, 1965 [July 10, 1964], No. 28715/64. Heading G6C. A reactor has control elements of large neutron absorbancy for normal control and and shut - down functions and additional control elements of small neutron absorbancy intended for deep insertion in the reactor core during full-power operation for controlling the excess reactivity provided for xenon over-ride and for operation by auto-control where provided, each additional control element being in copositional relationship with a control element of large neutron absorbancy. Preferably the control elements of large neutron absorbancy are tubular and of sufficient wall thickness as to absorb all neutrons of thermal energy, and the additional control elements fit within the bores of such of the tubular control elements with which they are associated. At the refuelling floor level of the reactor pressure vessel are disposed the accessible units for the control system of the reactor, one of such units 9 being illustrated diagrammatically in Fig. 2. This consists of a combined pressure vessel plug and winding unit and embodies its own electric motors. The control elements associated with each unit 9 comprise a tubular control member 10 comprising 4% boron steel sleeves contained end-to-end within a stainless steel tubular case, and a solid or tubular control rod 11 of stainless steel. The member 10 is provided with an annular lip at its lower end to co-operate with a circular plate at the top of the rod 11 so as to make it impossible for the rod 11 to leave the lower end of the member 10. Each unit 9 includes mechanism for separate control of insertion into or withdrawal from the control element channel 14 of both the tubular member 10 and the rod 11. The mechanism for controlling member 10 comprises a pair of winding sprockets 17 driven by a reversible electric motor, with chains 18, fixed at their upper ends to the casing of unit 9 and with slack loops 20, passing over the sprockets 17 and round pairs of guide sprockets 21, 22 and being secured at their lower ends 24 to the upper end of member 10. The rod 11 is controlled by a sprocket 25 disposed with its axis at right-angles to that of the sprockets 17 and driven by a reversible electric motor, controllable independently from that driving the sprockets 17, with a chain 26, fixed at its upper end 27 to the underside of unit 9 and with a slack loop 29, passing over the sprocket 25, round guide sprockets 30, 31 and being secured at its lower end 32 to the top of the rod 11. The control of the rod 11 is independent of that of the member 10 except insofar as the rod 11 cannot be lowered completely out of the member 10. An alternative construction is similar to that shown in Fig. 2 except that the control for positioning the member 10 and rod 11 is effective only on the former and is therefore simpler in construction, but allows auto-control employing the rods 11 only after withdrawal from the core of the members 10, whereas the former construction allows the use of some or all of the rods 11 for autocontrol without restriction.