GB1272296A - Nuclear reactor - Google Patents

Abstract

1,272,296. Reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. 29 April, 1970 [29 May, 1969], No. 27376/69. Heading G6C. In a reactor which is liquid cooled and has a positive void coefficient, e.g. a natural U fuelled, light water cooled, heavy water moderated reactor, the core is divided into groups of discrete elongate regions with the regions in each group spaced from each other both azimuthally and radially relative to an axis of the core and with each group of regions served by a separate coolant circuit. A reactor core shown in plan view in Fig. 1 has the fuel contained in tubes passing through a mass of heavy water moderator, pressurized light water flowing through the tubes in heat exchange with the fuel to generate steam. The core is divided into two groups of discrete elongate regions, one group being shown hatched and the other non-hatched. The regions are arcuate, being defined by dividing the core into six concentric zones A, B, C, D, E and F and six azimuthal sectors 1, 2, 3, 4, 5 and 6 about the longitudinal axis. Each group of regions is served by a separate coolant circuit including a circulator 7 and each circuit has flow control valves arranged in three groups of six valves, each valve controlling coolant flow to one region. Valves of the same number are ganged electrically so that coolant flow to any sector can be varied to effect spatial control. In a different control mode valves of the same character are ganged electrically so that coolant flow to the regions can be varied to effect radial flux shaping during approach to burn-up equilibrium. It is also possible to alter the position of any valve individually in order to correct the power distribution locally. In the event of loss of coolant from one circuit half of the core is voided but because the voidage is distributed throughout the core in several discrete regions the reactivity insertion is reduced typically by a factor of 1À5 from 2À9% to 1À9%. In an alternative embodiment (Fig. 3, not shown), each concentric zone and each azimuthal sector contains one region of each group, the regions of each group being disposed at progressively decreasing radii about the longitudinal axis.