GB1570471A - Process for the production of uranium and steel composite castings - Google Patents

Description

(54) A PROCESS FOR THE PRODUCTION OF URANIUM AND STEEL COMPOSITE CASTINGS (71) We NUKEM GmbH, a body corporate organised under the laws of Germany of 6450 Hanau 11, Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a process for the production of uranium and steel composite castings having abrasion-resistant cavity walls by casting uranium around corresponding hollow steel shapes.

By virtue of its specific properties, uranium metal, advantageously uranium depleted of the U-235 isotope, is eminently suitable for shielding against radioactive radiation. Accordingly, shielding elements of the type in question are used for storing encapsulated radioactive radiation sources of the type used for example in medicine and materials testing.

The shielding elements are produced in known manner by casting the particular geometries required and, in some cases, subsequently forming the transport duct or "depot" which receives the radioactive source.

The minimal abrasion resistance of metallic uranium is a disadvantage so far as the introduction and removal of the encapsulated radioactive radiation sources is concerned because of the danger of contamination. Accordingly, there is a need to improve this unfavourable abrasion resistance of the transport ducts or depots which are usually complicated in shape.

One known possibility of improving the unfavourable abrasion resistance of uranium is to introduce tubes or other shapes of a more abrasion resistant material.

On account of the generally complicated tube geometry, introduction is only possible by directly casting uranium around the tubes. Thus, tubes of zirconium alloys have already been used. Although abrasion resistance was improved in this way, significant disadvantages arose in the case of this material, being attributable above all to the fact that the tubes are rarely obtainable in the required dimensions, to the fact that difficulties are encountered in the dimensionally accurate bending into the generally complicated tube geometries and to the fact that the material costs are relatively high.

These disadvantages can be obviated by using steel tubes which, in addition, show even higher abrasion resistance. Unfortunately, the use of steel tubes is attended by the significant disadvantage that, when uranium is cast around the steel tubes, molten uranium (melting point 1132"C) alloys with iron from the steel tubes forming an eutectic phase which melts at as low as 725"C. Thus, the steel tubes are destroyed.

Accordingly, an object of the present invention is to find a process for the production of uranium and steel composite castings having abrasion-resistant steel cavity walls in which uranium can be cast around corresponding shapes of an abrasion-resistant material without a low-melting eutectic being formed and without any difficulties arising during the forming of these tubes.

The preset invention provides a process for the production of uranium and steel composite castings having abrasion-resistant steel cavity walls which comprises coating one or more shaped hollow steel sections with a layer of a ceramic material resistant to molten uranium (as hereinafter defined), and subsequently casting uranium around the steel sections thus coated.

As used herein, the term "resistant to molten uranium" means that the layer of ceramic material does not combine with the molten uranium, and in particular, does not form a low-melting eutectic with the uranium. Thus, the ceramic layer should not be chemically attacked by the molten uranium.

In one embodiment, an adhesion layer is additionally applied between the steel shape and the ceramic layer.

By virtue of the process according to the invention, it is possible to avoid the forma tion of the uranium-iron eutectic. The protection afforded by the invention against the attack of molten uranium is obtained by the application of a layer of ceramic material to the outer wall of the hollow steel shapes.

Although it has proved to be particularly effective to use a protective layer of Al2O3 it is also possible to use MgO or other ceramic materials which are resistant to molten uranium. An adhesion layer is with advantage additionally applied between the steel shape and the protective layer of Alp03.

This adhesion layer, which may consist of an aluminium-nickel alloy for example, is applied to the outer wall of the hollow steel shape before the actual protective layer.

Tubes are preferably used as the shapes.

In addition to aluminium-nickel alloys, nickel-chromium alloys and aluminiumnickel-chromium alloys may also be used for the adhesion layer.

It has been found that, in the case of Al2O3 protective layer thicknesses of from 0.1 to 1.0 mm are sufficient to prevent the steel tube from being destroyed by the molten uranium. It has also been found that a thickness of the adhesion layer of from 0.02 to 0.15 mm is totally adequate.

It has proved to be favourable to apply the relatively thin layers to the steel tube either by flame spraying or even by plasma spraying. The protective layers thus applied are extremely uniform and therefore completely ensure the protective effect.

The process according to the invention is illustrated by the following example: A steel tube bent in the form of a U is carefully cleaned over its surface and provided by flame spraying with a 0.08 mm thick adhesion layer of a nickel-aluminium alloy containing approximately 75 atom percent of aluminium. A 0.5 mm thick protective layer of aluminium oxide is then applied, again by flame spraying. The tube protected in this way is introduced into a chill mould in which uranium is cast around it at 1250 to 13000C. The steel tube withstands this treatment without damage; no iron-uranium eutectic is formed.

WHAT WE CLAIM IS: 1. A process for the production of uranium and steel composite castings having abrasion-resistant steel cavity walls which comprises coating the outer wall of one or more shaped hollow steel sections with a layer of a ceramic material resistant to molten uranium (as hereinbefore defined), and subsequently casting uranium around the steel sections this coated.

2. A process as claimed in claim 1, wherein the ceramic protective layer consists of aluminium oxide.

3. A process as claimed in claim 1 or 2, wherem an adhesion layer is additionally applied between the steel shape and the ceramic layer.

4. A process as claimed in any of claims 1 to 3, wherein the layers are applied by flame spraying or plasma spraying.

5. A process for the production of uranium and steel composite castings substantially as described with particular reference to the Examples.

6. A uranium and steel composite casting when produced by a process as claimed in any of claims 1 to 5.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. uranium. In one embodiment, an adhesion layer is additionally applied between the steel shape and the ceramic layer. By virtue of the process according to the invention, it is possible to avoid the forma tion of the uranium-iron eutectic. The protection afforded by the invention against the attack of molten uranium is obtained by the application of a layer of ceramic material to the outer wall of the hollow steel shapes. Although it has proved to be particularly effective to use a protective layer of Al2O3 it is also possible to use MgO or other ceramic materials which are resistant to molten uranium. An adhesion layer is with advantage additionally applied between the steel shape and the protective layer of Alp03. This adhesion layer, which may consist of an aluminium-nickel alloy for example, is applied to the outer wall of the hollow steel shape before the actual protective layer. Tubes are preferably used as the shapes. In addition to aluminium-nickel alloys, nickel-chromium alloys and aluminiumnickel-chromium alloys may also be used for the adhesion layer. It has been found that, in the case of Al2O3 protective layer thicknesses of from 0.1 to 1.0 mm are sufficient to prevent the steel tube from being destroyed by the molten uranium. It has also been found that a thickness of the adhesion layer of from 0.02 to 0.15 mm is totally adequate. It has proved to be favourable to apply the relatively thin layers to the steel tube either by flame spraying or even by plasma spraying. The protective layers thus applied are extremely uniform and therefore completely ensure the protective effect. The process according to the invention is illustrated by the following example: A steel tube bent in the form of a U is carefully cleaned over its surface and provided by flame spraying with a 0.08 mm thick adhesion layer of a nickel-aluminium alloy containing approximately 75 atom percent of aluminium. A 0.5 mm thick protective layer of aluminium oxide is then applied, again by flame spraying. The tube protected in this way is introduced into a chill mould in which uranium is cast around it at 1250 to 13000C. The steel tube withstands this treatment without damage; no iron-uranium eutectic is formed. WHAT WE CLAIM IS:

1. A process for the production of uranium and steel composite castings having abrasion-resistant steel cavity walls which comprises coating the outer wall of one or more shaped hollow steel sections with a layer of a ceramic material resistant to molten uranium (as hereinbefore defined), and subsequently casting uranium around the steel sections this coated.

2. A process as claimed in claim 1, wherein the ceramic protective layer consists of aluminium oxide.

3. A process as claimed in claim 1 or 2, wherem an adhesion layer is additionally applied between the steel shape and the ceramic layer.

4. A process as claimed in any of claims 1 to 3, wherein the layers are applied by flame spraying or plasma spraying.

5. A process for the production of uranium and steel composite castings substantially as described with particular reference to the Examples.

6. A uranium and steel composite casting when produced by a process as claimed in any of claims 1 to 5.