US3428770A - Induction furnace - Google Patents

Description

Feb. 18, 1969 A. BRIAND INDUCTION FURNACE Filed Dec. 16, 1965 1 v 4 7 In United States Patent U.S. Cl. 219-10.49 Int. Cl. H05b 5/02, 9/02 1 Claim ABSTRACT OF THE DISCLOSURE An induction furnace suitable for use in a nuclear reactor channel provides high temperature to the specimens being studied and has high heat dissipating power. The furnace is a mass of material having low electrical resistivity with a first bore therein containing an induction coil connected to an alternating current voltage source. A second bore is provided in the mass adjacent the first bore in which the test specimen is located. A gap communicates between the two bores. The induced current at the surface of the first bore flows around the gap and the second bore thus producing an alternating field.

This invention relates to an induction furnace which is mainly intended to constitute an irradiation furnace.

Said furnace is more especially designed for the purpose of heating a test specimen which is subjected to radiation treatment in a nuclear reactor or for the purpose of expanding specimens within a metallic mass as a result of thermal stress. However, said furnace can also be advantageously employed in all cases in which it is important to carry out the rapid cooling of a Specimen which has been heated to a high temperature, if necessary in an inert atmosphere or in vacuo.

In fact, the invention makes it possible to construct furnaces which have a high heat-dissipating power. Furnaces of this type can also be of small overall size, and this feature is especially useful in the case of irradiation furnaces which are intended to be introduced in a nuclear reactor channel with a view to heating a test specimen and studying the irradiation behavior of said specimen.

The induction furnace in accordance with the invention is characterized in that it comprises, pierced in a mass formed of material having low electrical resistivity, a first bore containing an induction coil which is connected to an alternating-current voltage source, a second bore which is intended to accommodate a test specimen, and a gap providing a communication between the two bores.

The induced current which is produced within the metallic mass at the surface of the first bore by the induction coil fiows around the gap and the second bore, thus producing an alternating field. Induced currents then pass through a conductor which is placed inside said second bore and which is thus heated without contact by Joule effect. The conductor referred-to can be the test specimen itself which is to be heated or a metallic cylinder containing the specimen in the case in which this latter is not conductive.

Thus, the specimen is no longer placed inside the induction coil as in designs of the prior art and the distance between the specimen and the metallic mass can be very small. This arrangement permits of very rapid cooling of the specimen through said mass, which is of particular interest in expanding operations which consist in heating to a very high temperature and in very rapid cooling. The operation can be performed in an inert atmosphere and even in vacuo.

In one particular form of embodiment of the furnace in accordance with the invention which is more especially 3,428,770 Patented Feb. 18, 1969 intended to constitute an in-pile irradiation furnace, means for cooling the metallic mass are provided. Said means serve to exert a cooling action on the specimen when this latter is subjected to intense internal heating as a result of irradiation, at which time the furnace itself is shut oil. When the internal heating stops as a result of shut-down of the reactor, the starting-up of the furnace makes it possible, by means of rapid heating, to maintain the same high temperature within the specimen.

In order that the characteristic features and essential advantages of the furnace according to the invention may become more readily apparent, there will now be given below a description of a particular form of embodiment, reference being made to FIGS. 1 and 2 of the accompanying drawings. The furnace herein described, which is not intended to limit the scope of this invention in any sense, is more especially designed to permit the heating and cooling of specimens placed in a channel of a swimming-pool reactor for irradiation purposes.

In the accompanying drawings:

FIG. 1 represents a diagrammatic part-sectional view of the furnace according to the invention,

FIG. 2 is a transverse sectional View showing the two bores.

In accordance with the invention, the furnace described comprises a coupling block 1 consisting of a metallic mass of parallelipipedal shape which is pierced by two vertical bores 2 and 3. Said bores are interconnected by means of a gap 4 which is of small width compared with the diameters of said bores and which is formed in the coupling block 1 parallel to the common direction of their axes, that is to say vertically in FIG. 1. However, the bores need not necessarily be parallel in order to ensure satisfactory operation and can be inclined to each other at an angle of 45, for example.

In the particular case described, the metallic mass 1 is formed of aluminum; this material has been chosen not only by reason of its good electrical conductivity but also on account of its properties under irradiation and especially its relatively low temperature rise under 7 radiations which permits of its use under high-flux conditions. However, in the case of other applications such as expanding, it would be more advantageous to employ copper since high electrical conductivity is an essential property required from the material which constitutes the metallic mass.

Two tubular sleeves 6 and 7 are welded to the top face and underface of the metallic mass 1 respectively.

Said two tubular sleeves are also formed of aluminum. The top end of the tubular sleeve 6 is adapted to fit over a conical bearing surface which is formed on a top closure plate 8. Similarly, the tubular sleeve 7 rests on a conical bearing surface of the bottom closure plate 10. O-ring seals 11 and 12 provide leak-tightness between each sleeve and the corresponding closure plate. A coupling is provided between the coupling block 1 and the closure plates 8 and 10 by means of rods 14 which also serve to compress the seals 11 and 12. By means of this arrangement, the furnace can readily be disassembled with a view to gaining access to its different elements and, in particular to the test specimen.

A helical coil 16 of copper is placed inside the bore 2, namely the bore which has the largest diameter. Said coil is connected by means of a coaxial line 17 to a highfrequency alternating-current voltage source which is not shown in the figures. The coaxial line 17 passes through the top closure plate 8, the necessary leak-tightness 'being ensured by means of seals which are not shown.

A pipe serves either to create a vacuum within the furnace by connecting said pipe to a pump set or to introduce an inert gas such as helium within said furnace.

A hollow metallic cylinder 20 which is formed either of molybdenum or niobium has an external diameter which is slightly smaller than the diameter of the second bore 3 and traverses this latter. Said cylinder 20 is supported by the bottom plate 10, in which one of its extremities is inserted. Said cylinder constitutes the specimen carrier, the element to be heated being expanded in that portion thereof which is placed inside the bore 3. In fact, the furnace is designed to permit the irradiation study of nuclear reactor fuel elements consisting of ceramic materials which are not electrically conductive. In the case of electrically conductive fuel specimens, the cylinder 20 could be full and be constituted by the test specimen itself.

A thermocouple 22 which traverses the top closure plate 8 makes it possible to measure the temperature inside the cylinder 20 immediately above the level of the test specimen.

Finally, the coupling block 1 is traversed by a number of loops of a pipe 23 which can be supplied with coolant water.

As a result of heat conduction through the coupling block 1 and the specimen-carrier cylinder 20, said coolant water system efiects the cooling of the test specimen when intense internal heating is produced within this latter as a result of the irradiation to which the specimen is subjected during operation of the swimming-pool reactor in which the furnace is placed. The coil 16 is then no longer energized.

Conversely, when the reactor is shut down, the water supply to the pipe 23 is cut off and the furnace is put into operation in order that a temperature should be maintained within the test specimen which is the same as the temperature maintained during irradiation. A high-frequency alternating current is supplied to the coil 16, thus intiating the appearance of currents which are induced within the coupling block 1 at the surface of the bore 2. These currents are intended to pass along the gap 4 and around the bore 3 by reason of continuity. The flow of current around the bore 3 creates a high-frequency field within this latter and the specimen carrier 20 then passes induced currents which lead to the heating of said cylinder by Joule effect. As a consequence, the test specimen which is in contact with said cylinder is also heated.

The temperature of the test specimen is measured by means of the thermocouple 22. Said thermocouple can be connected to a regulating unit which automatically controls the voltage or intensity of the current which is supplied to the induction coil as a function of the temperature of the specimen.

Whenever it may be found desirable to cool the test specimen, for example as soon as internal heating is produced within said specimen, the coil 16 is de-energized, with the result that the heating immediately stops, the coolant water again circulates through the pipe 23, and the coupling block ensures rapid heat removal from the specimen.

In fact, the furnace in accordance with the invention makes it possible to attain particularly high heat-dissipation values. The characteristics of a particular furnace as constructed in accordance with the foregoing description are mentioned hereunder by way of example. It will be understood that these characteristics depend on the relative resistivities of the diiferent elements and on the frequency of the current employed. Said characteristics are also dependent on the clearance which is provided on the one hand between the induction coil 16 and the bore 2 and on the other hand between the cylinder 20 and the bore 3, as well as on nature of the fluid which is contained within this space.

The particular case considered relates to a furnace which makes it possible to reach operating temperatures of 1400" C. and calls for the use of a niobium specimen carrier in the form of a cylinder 20 millimeters in diameter which is heated to a height of 60 millimeters. The coupling block is water-cooled at approximately 20 C. and heatdissipation values of the order of 30 to 40 w./cm. have been noted. The clearance between the niobium cylinder and the surface of the bore 3 was 2 millimeters. By reducing this clearance to l millimeter, heat-dissipating values of the order of w./cm. can be obtained. These figures are to be compared with the 10 to 15 w./cm. of conventional induction furnaces.

A further advantage of the furnace in accordance with the invention lies in the fact that the induction coil 16 remains practically cold during the operation of the furnace and consequently prevents any danger of seizure in the hot state between the induction coil and the specimen carrier as was liable to arise in irradiation furnaces of the prior art. Furthermore, the specimen-carrier cylinder or the induction coil can readily be disassembled independently of each other.

As will be apparent, the invention is not limited in any sense to the particular form of embodiment which has been described in the foregoing solely by way of indication. On the contrary, this invention includes within its scope any alternative form of either all or a part of those constituent elements thereof which remain within the definition of equivalent means.

What I claim is:

1. An induction furnace comprising a coupling means of material having low electrical resistivity, a first cylindrical bore in said mass, a helicoidal induction coil in said bore connected to an alternating current voltage source, a second cylindrical bore in said mass for a test specimen, a gap extending between and providing communication between said bores, means for cooling said mass including a plurality of passages in said mass for the circuation of a cooling fluid, a hollow metallic cylinder in said second bore containing the test specimen, a first tubular sleeve in fluid-tight engagement with said mass enclosing said coil and said cylinder and a second tubular sleeve in fluid-tight engagement with and on the opposite side of said mass from said first sleeve enclosing said cylinder.

References Cited UNITED STATES PATENTS 2,785,265 3/1957 Salisbury 219l0.79 2,882,378 4/ 1959 Ticehurst 219-l0.79

FOREIGN PATENTS 380,471 9/ 1932 Great Britain.

RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner.

U.S. Cl. X.R. 21910.79

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