GB1026845A - A fuel-rod assembly for liquid-cooled nuclear reactors - Google Patents

Abstract

1,026,845. Reactors. LICENTIA PATENTVERWALTUNGS-G.m.b.H. Feb. 6, 1963 [Feb. 6, 1962; Jan. 30, 1963], No. 4822/63. Heading G6C. A fuel element (Figs. 1a, 1b, not shown) comprising fuel rods 6 disposed within an annular channel 5 between coaxial tubes 4, 7 has a number of baffles 12 disposed helically round its longitudinal axis and provided with bores to receive the rods 6 so that coolant flowing through the channel 5 has a transverse as well as a longitudinal component of flow. This overcomes the disadvantage with pure longitudinal flow that the coolant has a higher temperature adjacent the fuel rods which lie towards the centre of the core than adjacent those situated towards the edge of the core. In a light watercooled and moderated reactor employing fuel elements of this construction (Fig. 2, not shown) the water enters through a valve 28 at about 300‹ C. and is divided equally between an upper distributer ring 20 and a lower distributer system 16. From the latter, the water flows up supply tubes 11 housed within inner moderator compartments 10 of the fuel elements to be deflected by the closed ends of inner casing tubes 9 down through the compartments 10 whence it rises outside outer casing tubes 2 through an outer moderator compartment 1 to flow laterally through a gap formed between a fuel element support grid 17 and a dividing plate 18 into a compartment 19 where it mixes with the water from the distributer ring 20. The water subsequently flows up through the channels 5 where it is preheated to critical temperature and then superheated to 600‹ C. The superheated steam is collected in an insulated dome 21 above the grid 17 and supplied to a turbine through an insulated conduit 24. The necessary pressure drop for the flow through the channels 5 is produced by a cushion of pressure gas 27 above the free surface 26 of the water, the pressure of which is regulated by a valve 33 and regulator 37 connected by a conduit 32 to a gas container 31, excess gas being released through a valve 38. The temperature of the superheated steam, measured by means of a temperature detector 30, is used to adjust the setting of control rods 29. Since, however, this adjustmen involves a few seconds delay, the control rods must be preliminarily adjusted directly by the turbine, the generator or the mains on variations in load and the temperature used only for fine adjustment. The water level in the reactor pressure vessel 14 is maintained constant by means of an automatic regulator 39. Emergency shut-down of the reactor is effected by forcing gas from the container 31 through a valve 35 in a conduit 34 into the distributer system 16 to displace the water from the moderator compartments 10 and the supply tubes 11, thus rendering the reactor sub-critical.