US3227798A - Bell furnace for the preparation of uranium metal by magnesiothermic reduction - Google Patents

Description

1966 M. DELANGE ETAL 2 3 BELL FURNACE FOR THE PREPARATION OF URANIUM METAL BY MAGNESIOTHERMIC REDUCTION Filed June 27, 1965 United States Patent O 3,227,798 BELL FURNACE FOR THE PREPARATION OF URANIUM METAL BY MAGNESIOTHERMIC REDUCTION Maurice Delange, Hennecy, Jean Sauteron, Itteville, and Paul Vertes, Antony, France, assignors to Commissariat a PEnergie Atomique, Paris, France Filed June 27, 1963, Ser. No. 291346 Claims priority, application France, July 6, 1962, %3,240 1 Claim. (Cl. 13-22) The present invention relates to an industrial furnace of the so-called bell furnace" type which is more especially designed for the fabrication of uranium metal in accordance with the rnagnesiothermic reduction process.

It is known that this process consists in carrying out in a refractory crucible the reduction of uranium tetrafiuoride with metallic magnesium for the purpose of obtaining cast ingots of uranium metal following the reaction: UF +2Mg- U+2MgF +76 kcal. at 800` C.

The heat thus evolved in the reaction is not sufficient to bring the mixture of uranium and magnesium fluoride to a temperature at which the viscosities of the two constituents permit of suitable separation of the metal from the slag. It accordingly proves necessary to carry out a preliminary heating of the reaction miXture of magnesium and uranium tetrafluoride for a period of time which is sutficient to ensure that the heat absorbed by said miXture is added to the heat evolved in the reaction -at the time of start-up of said reaction, thereby ensuring a perfect decantation of the metal.

The invention is concerned with the design of a furnace for the purpose of carrying out the above-mentioned reaction in which a variable addition of heat can be made in the reaction miXture, either for the purpose of initiating the reaction or for the purpose of accelerating the reaction, or again for the purpose of improving the yield by suitably shifting the equilibriurn of said reaction.

Another object of the invention is to make the operation of a furnace of this type particularly reliable by avoiding on the one hand any manipulation of the crucible itself during heating Operations and by permitting on the other hand the very rapid repair of this crucible in the event of leakage of magnesium and slag accompanied by ignition of the magnesum or in the event of fracture accompanied by leakage of uranium.

A final object of the invention is to obtain a substantial reduction in loss of time betwen two successive operations, thereby making it possible to increase the productivity of the installation without having any -adverse efiect on the reliability and safety of the plant as a whole.

The furnace in accordance with the invention is characterized in that it comprises a base or fixed supporting sole m ade of a refractory material on which is supported by means of a system which can be adjusted for height a crucible containing the reaction mixture, a movable bell which covers the crucible and which is adapted to rest on said fixed base in leak-tight manner through the intermediary of a sand packing which prevents any contact between the outer air and the interior of the bell, said bell being additionally provided With heating elements and safety devices which serve for the purpose of starting or controlling the reaction.

Apart from this principal arrangement, said furnace is characterized by various secondary arrangements which will be more specifically described below and which relate more especially to the means employed for the purpose of carrying out the height-adjustment of the crucible in the interior of the bell and the means which are intended to produce the automatic interruption of the heating 3,227,798 Patented Jan. 4, 1966 process as soon as the bell is separated from the fixed base on which it is supported.

The invention will in any case be more readily understood from the complementary description which follows below and which relates to one example of embodirnent, this example being given by way of indication and not in any sense by way of limitation. In the accompanying drawings, the single figure represents a diagramnatic View in vertical cross-section of a bell furnace which is employed in accordance with the invention for the preparation of uranium by magnesiothermic reduction.

The furnace comprises a fixed base or supporting sole 1 of re fractory material which is supported by pillars such as the pillar 2 on the bottom 3 of a tank constructed of concrete, for example.

The central portion of the base 1 is pierced with a bore providing a passageway for a support 4, the position of which c-an be adjusted for height by means of jacks 5 or by means of any other suitable lifting devices providing either continuous or non-continuous lift and located beneath the base in the interior of the tank.

The said support comprises a metallic plate 26 on which rests the bottom of the crucible '7 to be heated, said crucible being preferably constructed of steel with an internal lining consisting of a layer of refractory material. The crucible is provided externally with welded reinforcing members or stay-plates 8. The said crucible is provided at the bottom with a closure plate which is bolted onto a ange 9 on which is fixed a second closure plate 1@ by means of screws such as the screw 11. The plate ll@ is fitted with a lifting ring 12 by means of which the crucible can be either set in position or withdrawn after completion of the reaction and cooling.

The furnace proper consists of a bell 13 forming a casing around the cruci-ble and adapted to rest on the fixed base 1. The said bell is provided at the top with a yoke fitted with a lifting bar 15 on which is hooked a pulleyblock 16 by means of which the positioning or the withdraWal of the bell 13 can be effected from an overhead crane, for example. There is mounted on one of the side walls of the bell 13 a box 17 in which is contained a set of electric cables and contactors for the purpose of supplying current to three electric circuits 18, 19 and 20 placed one above the other and by means of which th heating of the internal atmosphere of the bell 13 can be regulated in three separate zones. The electric cables, which are designated by the reference numeral 21 in the drawings, terminate at the bottom end of the box 17 in contact-pins 22 which are intended to fit inside sockets 23 through which current is supplied when the bell is placed in position on the base 1. At the time of positioning of the bell, the contact-pins 22 in fact fit into the sockets 23 while the leak-tight joint between the bell and the base is formed by the penetration of an annular portion 24 which is integral with the bottom portion of the bell into the interior of a sand packing 25 which is provided at the periphery of the base. This arrangement accordingly makes it possible if necessary to put the interior of the bell under an inert atmosphere with a View to preventing the degradation of the crucible as a result of oxidation. A further result of this arrangement is to etlect the automatic interruption of the supply current to the three heating zones as soon as the bell no longer rests on the fixed base of the furnace.

In order that the commencement and suitable carrying on of the reaction inside the crucible may also be facilitated, the flange 6 on which the crucible 7 rests is placed on the steel plate 26 which covers the top face of the support 4. A hollow metallic tube 27 is additionally secured to the plate 26. Said tu-be 27 transmits after having passed through the fixed base 1 the vibrations of the plate 26 to a probe 28 which is in turn connected to an amplifier and to a control device 29 such as a loudspeaker, for example, thereby providing a means of detecting the start of the reaction.

Among the advantages provided by the bell furnace which has just been described, particular emphasis should be laid on the safety which is provided for the Operating staff and which is afforded throughout the installation as long as the various Operations are in progress, by virtue of the fact that the crucible is maintained in a stationary position on a refractory support which is inmobilized while the reaction is carried on. As and when the sai-d reaction takes place, the temperature of the furnace is in fact in the vicinity of 700 C. The mechanical characteristics of the crucible are under these conditions poor and would make the handling of this latter a distinctly hazardous undertaking. In point of fact, it is precisely this handling operation which is avoided in the furnace considered inasmuch as it is the heating vessel which is adapted to move and not the crucible. In the event of any accident occurring, it can thus be seen that it is possible by quickly removing the bell to carry out very rapid repairs on the crucible, the voltage applied to the heating zones 18, 19 and 20 being automatically cut ofi as a result of the separation of the contact-pins 22 from the corresponding sockets 23.

A further advantage of this type of furnace results from the increase in productivity which said furnace achieves without any attendant reduction in reliability and safety. It is in fact possible to provide one additional base per movable bell in order to envisage the alternate use of said bases. The bells or heating vessels can also be employed again for a further operation as soon as one reaction has been completed, without entailing any need to shift crucibles which have been brought to a high temperature.

It will -be understood that the invention is not limited in any sense to the form of embodiment which has been described and illustrated and which has been given solely by way of example.

What we claim is:

Bell furnace 'for the preparation of uraniurn by ma gnesiothermic reduction comprising a fixed supporting base of refractory material, a system of adjustable height in said base, a crucible mounted on said system, a removable bell covering said crucible resting on said base, a leak-tight seal between said bell and said base, heating elements for said bell, said heating elements being electric resistances mounted within said bell divided into a plurality of groups located one above the other in said bell forming separate heating zones, rigid and insulated electric cables and contactors for said resistances mounted on an external wall of said bell, rigid and insulated supply leads in said base for said cables connected to said cables through said contactors when said bell rests on said base, removal of said bell from said base automatically breaking the connections between said leads and said cables at said contactors, said system comprising a movable plate and jacks supporting said plate and said seal comprising a sand packing in said base and an annular portion for said bell received in said packing.

References Cited hy the Examiner UNITED STATES PATENTS 1,564,235 12/1925 Harrington 13--22 X 1,678,875 7/1928 Rohn 13--22 X 1,739,958 12/1929 Farmer 13-22 X 2,3S4,523 7/1944 Koehring 13--22 X 2,966,537 12/1960 Witucki et al. 13--22 X ANTHONY BARTIS, Acting Pr'mary Examner. a

RICHARD M. WOOD, V. Y. MAYEWSKY,

Assistant Exam'ners.

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