EP0146778B1 - Container for final radioactive waste disposal - Google Patents

Description

The invention relates to a container for the final storage of radioactive waste with uranium as radiation protection material within the container walls.

Containers for radioactive material, which contain uranium as radiation protection material between an inner and outer shell of the container body, in the shielding lid and on the container bottom, are known for example from DE-A-2 304 665. The uranium castings used for this purpose in the form of depleted material must always be encapsulated in another material, since they are not resistant to oxidation and corrosion.

Since uranium is also anisotropic in its properties and therefore expands to different extents when heated in three dimensions, in contrast to the usual encapsulation materials such as B. steel, there can be warps when filling the container with strong heat-emitting radioactive substances or during the prescribed fire test (30 minutes at 800 ° C), which damage the container.

It was therefore an object of the present invention to provide a container for the final storage of radioactive waste with uranium as radiation protection material within the container walls, in which distortions at elevated temperatures are excluded and which is less susceptible to corrosion.

This object was achieved in that uranium alloys with 5 to 15% by weight of molybdenum and / or 2 to 15% by weight of copper and / or 1 to 5% by weight of zirconium and / or 0.5 to 5 as the radiation protection material % By weight of chromium and / or 0.5 to 2% by weight of nickel and / or 0.5 to 1.5% by weight of niobium and / or 0 to 5% by weight of iron, the rest uranium, can be used , the total content of the alloying metals 10 to 16 wt .-% and the addition of chromium and / or nickel and / or niobium must be at least 1.5 wt .-%.

These alloys have a much higher corrosion resistance than the pure uranium metal and known uranium alloys, so that they can be used directly as container and radiation protection material, with only thin sheets of 1 to 2 mm to retain the alpha and beta radiation emanating from the core and no thick-walled encapsulations or steel jackets are required. In addition, these alloys show practically no anisotropy with regard to different thermal expansion.

• a) 89 % Uran, 8 % Molybdän, 1 % Zirkon, 1 % Chrom und 1 % Nickel
• b) 88,5 % Uran, 5 % Molybdän, 5 % Zirkon, 1,5 % Niob
• c) 88,5 % Uran, 4 % Kupfer, 5 % Zirkon, 1 % Chrom, 1,5 % Niob
• d) 85 % Uran, 5 % Kupfer, 4 % Zirkon, 5 % Chrom, 1 % Nickel.

The following alloys have proven to be particularly advantageous:

• a) 89% uranium, 8% molybdenum, 1% zircon, 1% chromium and 1% nickel
• b) 88.5% uranium, 5% molybdenum, 5% zircon, 1.5% niobium
• c) 88.5% uranium, 4% copper, 5% zircon, 1% chromium, 1.5% niobium
• d) 85% uranium, 5% copper, 4% zircon, 5% chromium, 1% nickel.

These alloys are radiation-resistant and only show an approximately 10% lower radiation shielding effect than pure uranium. The production of the alloys during melting is without problems, as is the casting of the corresponding shaped bodies. Depending on the requirement for corrosion resistance in accordance with the different geological formations of the repositories, the additions of the alloy metals can be varied in the areas claimed.

The use of uranium alloys as radiation protection and container material has the further advantage that depleted uranium, which accumulates in large quantities during the enrichment of uranium-235 and must also be treated as radioactive waste, is simultaneously disposed of without the need for separate containers . The same applies to uranium that has been reprocessed several times from the reprocessing of spent fuel elements, which can no longer be used for fuel element production due to the accumulation of non-fissile uranium-236.

Alloying copper and zirconium to uranium primarily serves to improve the corrosion properties. The zirconium content should not be higher than 5%, otherwise the melting point of the alloy will be reduced too much. Alloying of iron is also possible, although here too no more than 5% may be added, since otherwise the melting point drops below 900 ° C.

In combination with chrome, nickel and / or niobium, molybdenum and zircon eliminate the anisotropy of uranium.

The container according to the invention normally consists of a cast body made of uranium alloy, which is surrounded by an approximately 2 mm thick sheet metal jacket, which shields the alpha and beta rays that originate from the uranium or its decay production. In addition, you can still use an additional outer shell, the material against corrosion, such as. B. brine, is stable. Copper-tin bronzes, titanium and nickel-based alloys are suitable for this.

The figure shows schematically a cross section through a container. The radiation protection material (1) in the form of a uranium alloy is surrounded on the outside by a thin sheet metal jacket (2).

Claims (1)

1. A container for the final storage of radioactive waste, with uranium as the radiation shielding material inside the container walls, characterised in that uranium alloys containing from 5 to 15 % by weight of molybdenum and/or from 2 to 15 % by weight of copper and/or from 1 to 5 % by weight of zirconium and/or from 0.5 to 5 % by weight of chromium and/or from 0.5 to 2 % by weight of nickel and/or from 0.5 to 1.5 % by weight of niobium and/or from 0.5 % by weight of iron, the remainder being uranium, are used as the radiation shielding material, wherein the total content of the alloying metals must be from 10 to 16 % by weight and the addition of chromium and/or nickel and/or niobium must be at least 1.5 % by weight.

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