GB924748A - Improvements in or relating to nuclear reactors - Google Patents

Abstract

924,748. Nuclear reactors. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. April 14, 1961 [Jan. 20, 1960], No. 2158/60. Class 39 (4). A plutonium - fuelled nuclear reactor has the fuel in clad sheet form arranged for fluid cooling on one face, the other face being in close proximity with a neutron moderating material. A fuel, the temperature of which can be allowed to rise several hundred degrees above the normal working temperature so that, in the event of coolant failure, the reactor will shut itself down due to its own negative temperature coefficient, comprises a cement of plutonium oxide and stainless steel particles clad in stainless steel sheet. Carbon dioxide is the preferred coolant and in the core arrangement shown in Fig. 4, flows in the spaces between hexagonal graphite cylinders 1 which are encased in the steel clad cermet sheet fuel 2 and so protected from the carbon dioxide which would otherwise oxidize the graphite at high temperatures. A preferred core arrangement is shown in Fig. 10 and comprises hexagonal graphite cylinders 5, each drilled to accommodate a plurality of steel clad cermet fuel tubes 6. The cylinders 5 are mounted between plates 14, 20, each plate 20 being attached by rods 25 to a shield plug 24 to which spring loading is applied, e.g. by Belleville washers 26, and each plate 14 having a conical collector 16 secured to it. This spring loading allows for swelling of the graphite cylinders under irradiation (Wigner effect). The conical collectors 16 are supported by a grid plate 17 mounted within the reactor pressure vessel 7 and integral with a thermal shield 29 inside which are further thermal shields 27, 28 spaced from each other and the shield 29. The upper end of the shielding is closed by a biological shield 30 of laminated steel and graphite which is bolted down to the thermal shield 29 compressing the core-loading springs. Lateral biological shielding (not shown) is outside the pressure vessel. The cooling gas enters the reactor through ducts 31 flowing up between the pressure vessel 7 and thermal shield 29 or between the graphite cylinders 5. These two coolant flows meet through ports 34 in the thermal shields 27, 28 and 29 and descend together through the fuel tubes 6 into the conical collectors 16 and thence through pipes 35, corrugated to allow for expansion, to a collector pan 36, leaving the reactor through ducts 37. A small bleed-in point 38 in the summit of the cover 39 of the reactor avoids stagnation of the gas in the upper part of the pressure vessel 7. On raising the shield 30 after the cover 39 has been removed, rollers mounted on a flange 41 of the pressure vessel 7 may be inserted into a track 40 cut into the shield which can then be rotated to provide access to any graphite cylinder 5 or fuel tube 6 through access holes 42 which are normally plugged with stepped plugs 43.