METHOD OF INFLUENCING THE REACTIVITY OF A GAS-COOLED PEBBLE-BED NUCLEAR REACTOR

摘要

1442525 Controlling nuclear reactors HOCHTEMPERATUR - REAKTORBAU GmbH and KERNFORSCHUNGSANLAGE JULICH GmbH 15 May 1974 [22 May 1973] 21564/74 Heading G6C In a gas-cooled, pebble-bed reactor reactivity control is exercised (to perform shut-down or normal regulation) by the introduction of neutron absorber spheres whose diameter(s) are selected, in accordance with a formula, such as to determine their distribution and movement in and through the bed. If the fuel spheres have a diameter D, the absorber spheres, which are of lesser diameter dA, must be such that where d z =D(2/#3-1) is the diameter of the largest possible sphere which can be accommodated, in the densest packing configuration, between three mutually contacting fuel spheres, and where d z +xd z =D(#2-1). Absorber spheres of differing diameters and/or in differing members may be fed into different sphecified radial zones of the core. In a particular example where fuel spheres have a diameter D= 6 cm., d z is 0À93 cm. and is the lower limit for the diameter of the absorber spheres, whereas d z +xd z is approximately 2À5 cm. and is the upper limit. Absorber spheres having diameters lying in this range become partly lodged in the bed and partly travel through it.