GB1041773A - Improvements in or relating to nuclear reactors - Google Patents

Abstract

1,041,773. Reactors. BABCOCK & WILCOX Ltd. Dec. 21, 1962 [Dec. 29, 1961]. No 46790/61 Heading G6C. In a heterogeneous boiling liquid nuclear reactor, pressure variations in the vapour space of a core chamber containing the reactor core and having in operation an upper vapour space and a lower liquid space effect regulation of liquid level in the core chamber tending by variation of moderation and hence of core reactivity to counteract the pressure variations. As shown, the reactor comprises a pressure vessel 2 housed within a biological shield 30 and containing a bell-shaped core chamber 6. A liquid space 12 of the core chamber G is in communication with a liquid space 14 of the pressure vessel 2. Suitably the moderator and coolant is light or heavy water, or a mixture of the two. In the latter case, provision may be made for reducing the ratio of heavy water to light water during the life of the fuel. Water is fed into the pressure vessel 2 through an inlet pipe 19 and steam removed from the core chamber 6 through an outlet pipe 18. The core 9 within the chamber 6 comprises an assembly of stainless steel or zirconium alloy clad, uranium oxide pellet-filled fuel pins and may also include fertile material, uniformly or non- uniformly distributed. Advantageously, the or more fertile material is included in the upper portions of the fuel pins which at the beginning of the life of the core are not immersed in the moderator. A burnable poison, preferably boron, may be dispersed in either the fuel or its cladding. During operation, the liquid level 22 in the annular space 7 surrounding the core chamber 6 is maintained substantially constant and any increase in pressure within the vapour space 16 of the core chamber 6 effects depression of the liquid level 28 in that chamber, whilst any decrease in the pressure results in a rise of the liquid level, the core output thus being maintained constant. Should the pressure in the vapour space 16 rise to reach a predetermined high value, relatively cool liquid is sprayed into the vapour above the liquid level 22 in the annular space 7 from a ring conduit 26 controlled by pressurestats (not shown) connected to and responsive to the pressure in the vapour space 16, condensation of the vapour being effected and this resulting in a rapid lowering of the liquid level 28 and a reduction of pressure in the vapour space 16. The biological shield 30 is provided with a cover 50 formed of an outer portion 54 surrounding a central portion 48 removable along with the pressure vessel 2, and a plug 53 secured to the inlet pipe 19. The portions 54. 48 and the plug 53 are of suitably stepped formation. Handling means is described for raising a spent reactor from its biological shield, lowering it into an adjacent storage chamber and placing a fresh reactor in the biological shield.