process for the manufacture of bodies of fuel elements and fuel elements for nuclear reactors and high temperature absorbers

摘要

1424389 Isostatically compressing nuclear reactor fuels HOBEG HOCHTEMPERATURREAKTOR - BRENKTELEMENT GmbH 20 Sept 1973 [20 Sept 1972] 44098/73 Heading B5A A process for isostatically compressing fuel or absorber elements for high temperature nuclear reactors comprises isostatically compressing a mixture of binder-containing graphite powder and coated fuel particles or absorber particles in a plurality of stages, each stage being carried out at a higher pressure than the preceding one and in a different rubber mould to obviate the need to remove air from the pressing powder and to minimize wear of the rubber, e.g. silicone moulds. To produce elements having a carbon only outer shell, three stages are required. The first stage comprises producing a porous core under low pressure, e.g. 15 kp./cm.SP3/SP from the above mixture. The second stage comprises applying a coating of binder-containing graphite powder to the porous core under a slightly higher pressure, e.g. 150-170 kp./cm.SP2/SP. The third stage comprises compressing the coated porous core under a high pressure, e.g. 2À5 tonnes/cm.SP2/SP. The binder, e.g. phenolic resin is then coked by heating the final pressing to 800‹ C. and calcining in vacuo at 1800‹ C. The mould for the final pressing may be evacuated. The moulds may comprise ellipsoidal or cylindrical cavities for producing spherical or cylindrical elements. Spacer ribs for cooling gas may be moulded in situ on the elements. The moulded elements may be trimmed to size.