FR2482764A1 - PROCESS FOR THE INCLUSION OF RADIOACTIVE METAL WASTE CONTAINING TRITIUM - Google Patents

Abstract

A. THE PROCESS IS INTENDED FOR THE INCLUSION OF METAL RADIOACTIVE WASTE, IN PARTICULAR WASTE CONTAINING TRITIUM FOR THEIR DEFINITIVE STORAGE. B. THE METAL WASTE IS INTRODUCED IN A METAL BODY WITH LITTLE PERMEABLE AT TRITIUM BEFORE BURNING THEM IN CONCRETE. C. THE PRESENCE OF THIS METAL PART PREVENTS THE RELEASE OF THE TRITIUM AND THE EXCHANGES BETWEEN THE WASTE DUCTS AND THE CONCRETE THANKS TO THIS ADDITIONAL BARRIER.

Description

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  The invention relates to a method for the inclusion of tritium-containing radioactive metal scrap, in particular sheaths of fuel elements and tritium-containing fines, which must be coated with concrete for permanent storage.

  When reprocessing combustion elements

  burnt, from light water reactors, radioactive solid waste is obtained in pieces containing tritium, especially fuel element sheaths, springs, bolts and other small parts, which must be stored

  so as not to harm the environment.

  In the current state of the art,

  obtained by inclusion of radioactive solid waste, containing

  tritium, in concrete, and final storage in a salt mine. As it is not excluded under these conditions that a tritium migration occurs in the concrete and thus a possible release of tritium has been formulated reserves

against this process.

  Other processes according to DE-OS 2 628 144 and 2 717 389 cor-

  solids are included by melting in a metal matrix.

  Inclusion is accomplished by filling the void spaces with a molten metal; consisting of aluminum or preferably low-melting metals such as lead, tin, zinc,

copper, or alloys.

  It has also been proposed to include by fusion

  sheaths of fuel elements in glass, and solidification

  proud of everything in a compact block with additives.

  However, all these processes have serious drawbacks, which are due to the use of temperatures

  elevated during the solidification process.

  Indeed, volatile radionuclides are then released from the materials to be included, in particular the

  tritium and ruthenium, which must be separated from

  and eliminated. In addition, the use of high temperatures makes it necessary to use high cost storage apparatus and drums, and it may occur because of

  differences in glass / metal or metal / metal shrinkage when cooling

  cracking, decreasing in the event of an incident

leaching.

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  The object of the invention is to find a process for the inclusion of tritium-containing radioactive metal scrap, in particular fuel element sheaths, in concrete, for permanent storage, which surely prevents release of tritium or other

volatile radioactive material.

  For this purpose, the invention proposes a process characterized in that the metal scrap is

  incorporated before their inclusion in the concrete, at low temperatures

  in a metal body with low tritium permeability. The

  pieces of tube of fuel elements, the pieces of

  Inner and inner parts are preferably poured into a metal container which, after cold forming by rolling or pressing, hermetically surrounds its contents. As containers, it is advantageous to use round or profiled tubes, closed on one side, of any metal, preferably stainless steel or aluminum. As the tube diameter, for example, nominal dimensions of 10 to 300 mm are used, for wall thicknesses of 0.5 to 3 mm. Incorporation by

  rolling in U-shaped profiles is also possible.

  Pieces of fuel elements containing tritium (about 5 cm long according to the shear process) are introduced into tube sections whose length is adapted to the intended cement block. The end of the tube is then closed by folding it so that the escape of air remains possible during the subsequent rolling or pressing. The material that is inside is then compacted and flattened. At the last pass in the rolling mill, the end open to gases must be

hermetically closed.

  When U-shaped profiles are used, they are stored by shaking, side by side a number of sheaths of other fuel elements in the matrix, and compacted by pressing. This last operation can be repeated several times. Then, the container is sealed by applying a lid by pressing or rolling. The compact product is in the form of a flat material and can be rolled to a shape suitable for compact storage, such as a spiral shape. Alternatively, the flat material can be introduced vertically into concrete drums. After loading the barrels, solidify

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  in a compact block by pouring concrete.

  Compared with the cementing of unconditioned duct sections, this method has the advantage of forming an additional barrier. Thanks to the container, an exchange between the material of the sheaths and the concrete is avoided.

  release of tritium and increase the resistance to lixi-

in the event of an accident.

  In addition to stainless steel and aluminum, it is also possible to use metals which are not very permeable to tritium, for example aluminum alloys. The pressing takes place at the

ambient temperature.

The invention will be better understood at

  using the examples described below.

EXAMPLE 1

  In several stainless steel tubes 650 mm long, closed on one side, having a wall thickness of 0.5-2 mm and an inner diameter of 50-300 mm, non-compacted sheaths are introduced. The ends of these tubes are closed by a cover, or flattened and folded. Each tube is then pressed in about 5 passes and rolled into a plate. Plates 100-450 mm wide and 700 mm long are thus obtained. They are arranged by means of spacers in a barrel, so that the wide plates are in the middle and the narrow plates on the outside. The empty space remaining in the barrel is then filled with liquid mortar or concrete. The casing capacity of the casks here is higher than with non-compacted sheaths, and the tritium content of the casings is sufficiently protected against any diffusion in the casing.

  cement by steel foriming barrier.

EXAMPLE 2-

  An aluminum tube 100 mm in nominal diameter 700 mm in length and a wall thickness of 1 mm is filled with sections of compacted and uncompacted fuel elements. 50 mm is left free at the ends of the tube. One end is flattened and folded before filling, and the other end is closed even after filling. The filled and closed tube is then subjected to a 2, slow pressing in a hydraulic press, 3 to 6 t / cm being necessary for this purpose. This also gives a plaque,

  ho in which the sections of fuel elements are complete

surrounded by the tube,

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Claims (4)

  1. A process for the inclusion of radioactive metallic waste, containing tritium, in particular sheaths of fuel elements, in concrete for final storage, characterized in that it is introduced into a low permeability metal body tritium waste   metal, before drowning in concrete.   2. A process according to claim 1, characterized in that the metal scrap is included by   rolling in us. metal with low tritium permeability.   3.- Method according to one of the   1 or 2, characterized in that the scrap metal is introduced into round or profiled tubes, that they are   compact by rolling and enclosed on all sides.   4. Process according to any one   Claims 1 to 3, characterized in that, as a material   low permeability to tritium, use is made of stainless steel,   aluminum or aluminum alloys.