Patent GB-954718-A (GB)
Title: Improvements in or relating to high temperature gas cooled reactors
Inventor: KINSEY DENIS VICTOR
IPC: G21C5/12
Filed: 1962-03-28
Abstract: 954,718. Nuclear reactors. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. March 28, 1963 [March 28,1962], No. 11842/62. Heading G6C. In a gas cooled high temperature reactor having a channel for leading purge gas along a flowpath extending in close proximity with fuel bearing core materials, which at operating temperature is susceptible to corrosion by reactions between the material and substances entrained in the gas, a porous body of chemically reactive material capable of extracting said substances from the gas is located in the flowpath at a position upstream of the region in which the fuel bearing core material is located. Figs. 2A and 2B show the upper and lower halves of a fuel element cluster, each fuel element comprising a hexagonal graphite tube 18 secured at its upper and lower ends to a graphite block 16 and a fitting 17. The tubes 18 are cooled by helium flowing round the outside, and these ports 22 (of which only one is shown) at the upper end of each tube 18 allow part of the helium coolant to pass inside the tube as a purge gas flow to remove fission products from the fuel member 11a. The purge gas flows into a graphite cannister 23 containing a graphite filter 24 for removing dust particles and forming a pressure dropping orifice. Beneath the cannister 23 is a cartridge 26 of porous graphite material made reactive by a catalyst to remove inpurities such as carbon dioxide and water vapour from the helium. The catalyst may be barium, strontium, or nickel or a gettering metal such as titanium or zirconium. Centrally within the tube bore and beneath block 26 is a spine 27 formed in short tubular lengths each long enough to support three annular fuel cartridges 11a; these fit loosely within the bore and on the spine and have longitudinally extending grooves at spaced regions of the periphery to provide clearance for purge gas flow, and annular chambers 11d are formed at each end to provide a continuous path whether or not the grooves are in alignment. The lower end of each fuel element includes a fission product trapping compartment, mainly for trapping halogens, comprising a rod 33 having eight longitudinal grooves 34 filled with porous material. The centre portion of rod 33 supports the fuel tube internals above it and is seated on a bed 35 of permeable filter material. By arranging that the fuel tube 18 is formed of a more permeable graphite a continuous inward diffusion of gas, against the possible outward diffusion of fission products, may be established. The chemical reactivity of the graphite used for fuel compacts or fuel spines or fuel tubes may be reduced by incorporating small amounts of substances which suppress the catalytic activity of barium and strontium fission products, e.g. oxides of silicon, zirconium, or aluminium. Outside the reactor the purge gas flow leads to a sampling means and a filter, whence the clean gas is returned to the main volume of coolant; means are also provided for measuring the pressure drop in the purge gas across each fuel element.