GB981424A - Improvements in or relating to heterogeneous nuclear reactors - Google Patents

Abstract

981,424. Nuclear reactors. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. June 16, 1961 [July 15, 1960], No. 24720/60. Heading G6C. A heterogenous nuclear reactor core comprises tubes 15 containing sheathed fuel elements 16 disposed in a heat transfer fluid, and being interconnected so that, in relation to a cooling fluid passed over the tubes 15, the heat transfer fluid proceeds first in one tube 33 in the same direction as the cooling fluid and then in an adjacent tube 35 in the opposite direction, the tubes being so constructed that heat transfer between the two fluids is reduced when they flew in the same direction and increased when they flow in opposite directions. The invention is described with reference to a boiling water reactor and, as shown in the section in Fig. 2, pressurized water is circulated up one tube 33 between the fuel elements 16, in a direction parallel to that of the flow of a water coolant/moderater outside the tubes 15, into the portion of the tube 33 above the fuel elements 16 which contains a heat insulator 34. This is preferably a thin sleeve supported with clearance within the tube 33, the annular space between it and the tube being closed at one end and containing stationary water. The pressurised water then flows through a coupling 20 to the tube 35, the upper portion of which has longitudinal fins 36 on its outer surface and contains a plug 37 to increase the flow velocity of the water. The upper ends of the tubes 15 are provided, above the water level in the reactor pressure vessel, with spaced circumferential fins 32, those of one tube interlacing with those of adjacent tubes so as to serve as a steam separator. The circulating pressurised water loses little heat in the tube 33 but, over the longitudinally finned length of the tube 35 where a counter-flow relationship exists between the pressurized water inside the tube and the steam from the reactor coolant/ moderater, the pressurized water superheats the steam to a temperature near that which it itself attains. Since only half the tubes 15 are effective for superheating purposes, the flow of steam may be given a cross-flow component by means of a frusto-conical baffle plate situated above the separator section and differential heat transfer arrangement shown in Fig. 2. Each of the tubes 15 contains a group of juxtaposed sheathed fuel elements of circular cross-section, there being three, viz. 28, 29 and 30, in the illustrated example (Fig. 3). Wound round the sheath of each element is a helical spacing wire 41 of such a diameter that the three elements fit snugly in a triangularly arranged bundle in the tube, one element being inserted with the wire helix oppositely handed to the other two. Specification 981,423 is referred to.