FR2458879A1 - EXTRACTION COLUMN FOR FISSION MATERIALS AND / OR RAW MATERIALS - Google Patents

Abstract

A. EXTRACTION COLUMN, FOR FISSION MATERIALS OR BURNT MATERIAL TREATMENT, WITH SAFE GEOMETRY AND HIGH FLOW RATE. B. CHARACTERIZED IN THAT THROUGHOUT THE LENGTH OF COLUMN 1 ARE AVAILABLE ONE OR MORE RODS 2 INCLUDED WITH A NEUTRON POISON. C. DEVICE APPLICABLE TO THE TREATMENT OF BURNT NUCLEAR FUELS.

Description

The invention relates to a column, in particular

  bonding an extraction column for fission materials and / or raw materials, with high safety geometry and high throughput. In the nuclear industry, particularly during the reprocessing of burned fuel elements, uranium and plutonium are purified by liquid-liquid extraction. Depending on the content of the U-235 and plutonium solutions, a certain diameter of the cylindrical columns used must not be exceeded, for reasons of divergence. This restriction therefore limits the

flow extraction columns.

  In large instalations, therefore, several extraction lines must be arranged in parallel (a line comprising, for example, 3 to 6 columns), which leads to

high investments.

  Increasing or doubling the flow of the columns, as would be desirable, would not only save the cost of additional extraction lines, but also the production space, which is particularly expensive, for example in the case of reprocessing plants, by following the thick

  concrete shielding necessary for the protection of the environment.

  It has already been proposed to carry out poisoning

  heterogeneity of the column with hafnium-metal (Reaktor-

  tagung Dt 8.eldorff 1976). According to this method, the perforated plates of the column must be constituted by hafnium sheet

about 2.5 mm thick.

  This proposal is, however, linked to a series of disadvantages. Thus, the geometry of the column does not allow significant magnification, the flow can not be doubled. In addition, stress corrosion can not be ruled out, since the column is made of stainless steel and

  that local attacks can occur. In addition, the thick

  perforated trays should often be checked, as the increase of this thickness

  calculation of the absorption, and increases the divergence.

  The object of the invention is therefore to provide an extraction column for fission and / or raw materials, with a safety geometry and a higher flow rate, which does not have the drawbacks mentioned above, 2.- but allows to obtain a much higher flow, without

  that there are problems of corrosion.

  For this purpose, the invention is characterized in that disposed in the column, over its entire length, one or more rods provided with a neutron poison. One or more rods are preferably placed in the column in the central position, the columns other than extraction columns, such as those for grinding or washing, may be provided with rods in the same manner, and may also comprise inserts as per example trays or filler materials. A single central neutron absorption rod is preferably employed. The figure schematically represents a

  1-5 embodiment of the column according to the invention.

  In the column 1 provided with inlet and outlet pipes for the various liquids, for example the extraction agent and the solution to be extracted, is disposed a rod 2, which has at the level of the foot 3 and the head 4 of column 1, a larger diameter, corresponding to the outer farm of column 1. At these points of the column, wider in diameter, it is also possible to incorporate additional rods. The rod 2, arranged in this case

  centrally, is constituted by a sheath 5, the inte-

  laughter 6 is filled with neutron poison. The column has

in addition perforated trays 7.

  Preferably at the center of column 1 is a central hollow rod 2 of the same material as the column itself, filled with neutron poison. This central tube filled with neutron poison, and closed on all sides, can be enlarged at will, so that the diameter of the column can also be enlarged practically at will, so that one can have a surface section

  much higher, and so is the flow rate.

  In the purification of natural uranium we already know column diameters of one meter (without central rod) and we can now use them (with central rod) also for enriched uranium and plutonium. Corrosion

  tension is excluded due to the unique material of the column.

  To indicate that it can not come out of the rod of the 3. Neutron poison by dissolution, it is interesting to incorporate

  on rod 2 a leak indicator, which also gives the alarm

  if a fluid seeps in. This can prevent costly controls. As the neutron absorbing material, it is possible to use, for example, boron carbide (B 4C) in the form of compact powder or tablets, cadmium metal also in the form of alloys, or gadolinium oxide (Gd203) and

  other rare earths (Dy2O3, Sm203 etc ...).

  The most advantageous is cheap boron carbide; only in rare cases is it necessary to use higher absorption sections of the material for neutrons. The tube of the central rod is made of the same material as the column with equal or lower wall thickness, it is filled for example with B4C powder and sealed welded. This central tube serves for example simultaneously to support the perforated trays which are arranged over the entire height of the column about every 5 cm. The expanded settling space, at the foot and at the top of the column can also be equipped to avoid divergence by neutron absorbing rods of a proportionally greater thickness. Enlargements of this order (stabilization zones) are required to keep the phase boundary important.

  for the control of the column, free of flocculation.

  The invention will be better understood with the aid of the examples described below.

EXAMPLE 1

  For a solution of uranyl nitrate, with a 4% enrichment in U235, the safety diameter of the column is 38.5 cm. In order to double the flow of a

  any column, the double passage area is required.

  The safety diameter of the column, 38.5 cm, corresponds to a passage area of 1164 cm. A double area of 2328 cm 2 can be achieved if the diameter of the column is enlarged to about 58 cm, and the central neutron absorption rod has a diameter of 19.5 cm and is filled with, for example, boron carbide. powder. The diameter of the column, 58 cm, then corresponds to a passage surface of 2642 cm, which is decreased by about 300 cm 2 by the central absorption strip, so that there remains a surface of passage of

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  2342 cm2, which substantially allows to double the flow.

  If we enlarge at the level of the phase limits,

  at the head or the foot of the column, the area of passage of

  Viron 3 times, as usual, then the column ends have a diameter of 56 cm. The absorption rod can then be constituted by a piece whose thickest ends are always thinner than the diameter

inside the column.

EXAMPLE 2

  For plutonium nitrate solutions, the safety diameter of the column is 15 cm. To double the flow it takes a double passage area. A column 15 cm in diameter has a passage area of 177 cm 2 so that to double the flow, it takes a surface of

passage of 354 cm.

  With a central absorption rod (filled with B4C), a column has the following measures for a double flow: - diameter of the column = 22.5 cm with S = 398 cm2 - diameter of the rod: 7.5 cm with S = 44 cm at B4C - from where a free passage area of S = 354 cm The widened column ends have a diameter of 37 cm, the ends of the absorption rod

have a diameter of 22 cm.

5.-

Claims (7)

CLAIMS.   1.- Extraction column, for fission or burn material, with high safety geometry and high throughput, characterized in that the whole length of the column (1) is arranged one or more   chopsticks (2) provided with a neutron poison.   2. Column according to claim 1, characterized   in that the rods (2) are arranged in the column in central position.   3. Column according to one of claims 1   and 2, characterized in that the rods (2) are constituted by a sheath (5) whose interior (6) is filled with a poison with neutrons.   4.- Column according to any of the   Claims 1 to 3, characterized in that the sheath (5) of   the rod (2) consists of the same material as the column (1).   5.- Column according to any one of   Claims 1 to 4, characterized in that the chopsticks (2)   are equipped with a leak indicator.   6.- Column according to any of the   Claims 1 to 5, characterized in that the rods (2)   are widened at both ends in such a way that the security of divergence is ensured even in the stabilization zones widened column.   7.- Column according to any of the   Claims 1 to 6, characterized in that only   a single rod (2) arranged centrally.