GB795406A - Improvements in or relating to nuclear reactors - Google Patents

Abstract

795,406. Nuclear reactors. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. March 4, 1957 [March 5, 1956], No. 6836/56. Class 39(4). A nuclear reactor comprises fuel elements of such shape and dimensions as to provide a smooth continuous surface, a further continuous surface closely adjacent to said surface to define a passage capable of supporting a climbing film system when the reactor is in operation, and means for feeding coolant liquid to the lower end of the passage at such a pressure head and feed rate that a climbing film system is set up. Fig. 2 illustrates the behaviour of a coolant liquid as it passes upwardly through the annular space between a fuel element 12 and a coolant tube 1. In region A there is normal ebullition, and in region B discrete annular slugs of liquid 15 surround annular vapour slugs 16. In region C a climbing film system is set up with liquid films attached to the coolant tube 1 and to the fuel element 12 and vapour in the annular space between ; finally in region D there is a spray region where the films are disrupted. The onset of this spray condition should be avoided except where a ceramic type of fuel element is used over this region. Fig. 1 shows a reactor in which the climbing film region can occupy 60-80 per cent of the total height of the coolant tube and the spray region eliminated by choosing appropriate dimensions and by adjustment of the coolant pressure head and feed rate. The steam produced and the residual coolant liquid leave the coolant tubes at the top and the two phases are separated by individual separators 19. The bulk moderator fluid 8 and the coolant liquid are the same, e.g., water or heavy water, so that the separated liquid may be passed directly into the bulk of the moderator. The steam passes out of the pressure vessel to turbines 21 after which it is condensed and returned to the coolant header tank 10. In an alternative arrangement the coolant tubes 1 pass into a common header and thence to a single external cyclone separator ; this may be better if the coolant liquid is not the same as the moderator liquid.