Platinum Metals Rev., 1958, 2, (2), 63
Vacuum Casting Uranium Reactor Fuel Elements
Temperature Control with Platinum Thermocouples
Among the final operations at the Spring-fields Works of the United Kingdom Atomic Energy Authority is the vacuum casting of high-purity uranium into rods for use as reactor fuel elements.
The Springfields Works undertakes the preparation of almost all the uranium refined in Britain, starting from the ore. After a series of chemical treatments, uranium tetra-fluoride is reduced with metallic calcium by firing in a reduction mould.
To produce the reactor fuel elements in the required shape and size, and also to remove metallic and non-metallic impurities, the uranium is then melted and cast in a group of high-frequency vacuum furnaces. These are of the stationary-crucible, bottom-pouring type, the base of the crucible being pierced by a pouring hole, closed during melting by a graphite or alumina bung.
For successful casting the pouring temperature is critical, and is controlled by means of platinum: rhodium-platinum thermocouples led in through the top of each furnace. When correct pouring temperature has been attained, the bung is removed by means of a graphite rod and a system of bell cranks, push rods and levers, and the molten uranium runs through a launder into the moulds stationed in the lower part of the furnace.