GB2141866A

GB2141866A - Method of decontamination of radioactively contaminated scrap iron and/or steel

Info

Publication number: GB2141866A
Application number: GB08411358A
Authority: GB
Inventors: Eike Gelfort
Original assignee: Deutsche Gesellschaft fuer Wiederaufarbeitung von Kernbrennstoffen mbH
Current assignee: Deutsche Gesellschaft fuer Wiederaufarbeitung von Kernbrennstoffen mbH
Priority date: 1983-05-20
Filing date: 1984-05-03
Publication date: 1985-01-03
Also published as: DE3318377A1; FR2546332B1; DE3318377C2; JPS6037000A; FR2546332A1; BE899697A; GB8411358D0; GB2141866B; BR8402397A

Abstract

In decontaminating radioactively contaminated scrap iron and/or steel, the scrap is smelted in the presence of slagging agents, and to reduce further the residual radioactivity, inactive isotopes of the radioactive elements present in the melt are added and likewise subjected to the smelting process. By this means, according to the solubilities specific to the particular elements, the radioactive isotopes of the elements get driven out of the melt and go into the slag which is separated from the melt. In this way an iron or steel melt is obtained having a residual radioactivity so small that reuse of the iron or steel is possible.

Description

SPECIFICATION Method of decontamination of radioactively contaminated scrap iron and/or steel The invention refers to a method of decontamination of radioactively contaminated scrap iron and/or steel by smelting the scrap in the presence of slagging agents for the iron/steel smelting.

From the publication "Treatment of Metallic Wastes by Smelting" by J.H. Cavendish in the IAEA SM 234/14, a method is already known forthe decontamination of scrap steel contaminated by uranium-fluorine compounds, neptunium, plutonium and technetium, by smelting after previous chemical purification. A slagging agent is added to the melt in the form of a mixture of silica and lime, whereupon uranium, neptunium and plutonium are very largely precipitated into the slag which is then separated. By this method the disposal of refuse is simplified through the reduction achieved in the volume of non-reusable portions of scrap. Furthermore reuse is proposed of the weekly radioactive material left behind in the melt.

A method has also already been proposed for the decontamination of lead, cf. Cerr6 P., Mestre E., Courtauld J.; La decontamination du plomb; Bulletin Informatiques Scientific et Techniques 69; pages 49 58(1963). As is well known, lead - usually in the form of lead bricks - is employed for the screening of high-energy radiation in laboratories and similar equipments. Because of the high cost of the material, reuse of the contaminated lead was already striven for at an early stage.

In the case of the disposal to waste of shutdown nuclear power stations there are obtained from the region of the reactor core relatively highly activated components, which for transport to final storage need powerful screening. Moreover large amounts of contaminated steel parts must be disposed of to waste. It has already been proposed to melt down these contaminated steel parts and to produce from them screening which may be employed in the disposal to waste of highly radioactive refuse, cf. "Atomenergie/Kerntechnik", Volume 41 (1982), pages 279 - 280. This is a way which considerably reduces the volume of refuse and thereby the cost of storage in the final storage and opens up for the refuse an ingenious use.

The present invention is concerned with scrap iron and/or steel which is contaminated radioactively on the surface, such as is obtained, e.g. from reprocessing plants. In that case it is to be observed that large smooth areas can be decontaminated rapidly, whilst recesses, corners, cracks, sockets and closed ends of tubes demand a greater outlay. Since the radioactive contamination in the surface regions exhibits a distrubution in depth having an exponential trend, a point can be found beyond which the outlay upon conventional measures of decontamination does not stand in an economic ratio to further lowering of the radioactive radiation. The scrap steel will even then still exhibit a residual radioactivity.The amount of radioactivity refuse follows from the application of the boundary zone (the critical value between radioactive refuse and inactive refuse) on the basis of the corresponding legal regulations.

The residual radioactivity as a rule prevents direct utilisation of the scrap steel. This scrap has to be treated as lightly radioactive refuse in such a way that it may be brought into end storage or it has to be decontaminated in such a way that it may be satisfactorily recycled.

The present invention seeks an improved method of decontamination of scrap iron and/or steel by smelting.

According to this invention we provide a method of decontamination of radioactively contaminated scrap iron and/or steel by smelting the scrap in the presence of slagging agents for the iron/steel smelting, wherein inactive isotopes of the radioactive elements present in the melt are added in addition and subjected to the smelting process.

Preferably the inactive isotopes, which may be suitably added in the form of minerals are put into the melt.

Suitably, inactive isotopes of the elements strontium, barium, cerium, europium and zirconium are added.

The method of decontamination in accordance with the invention originates from the known method mentioned initially, of smelting the contaminated steel or iron and of slagging radioactive elements with which the surface of the steel or iron is contaminated. In the case of this known metallurgical smelting treatment a slagging of most of the radioactive elements is effected, i.e. the radioactive elements enter into intermetallic compounds which are lighter than the basic material and therefore collect in the slag on the surface of the melt. The slag with the bound radioactive elements can then be drawn off from the surface of the slag and processed into packs for final storage. But in the case of this known method of decontamination a noticeable residual radioactivity still remains, which makes reuse of the "decontaminated" scrap steel appear problematical.

The constituents of the slagging agents mentioned, such as are used, for example, in the case of the blast furnace process, are, for example: CaO 35 - 40 % T205 1% SiO 28-40% Na2O 0.1 % Awl203 5-13% K2O 2% MgO 2-13% FeO 1% MnO 10% where there are 300 to 800 kg of slagging agent to 1 ton of raw steel.

Through the measure in accordance with the invention, that is, the addition of inactive isotopes, one finds that, according to the solubilities specific to the elements, the radioactive isotopes of the elements get driven out of the melt and are collected in the slag. By this means a considerable reduction in the residual radioactivity is achieved, so that a steel melt results having a practically negligible radioactivity.

Since the amount of radioactively contaminated scrap from the shutting down and repair of nuclear plants is very extensive and causes heavy costs because of the volume which has to be prepared for underground final storage, the method in accordance with the invention shows considerable progress, since through the decontamination by smelting in accordance with the invention the volume of final storage may to a fairly large extent be saved. The raw steel gained from the melt may be recycled and reused. The radioactive slag is processed into refuse packs and needs a much smaller storage volume than the original contaminated scrap steel.

Through the method in accordance with the invention, the elements taken up are above all strontium, barium, cerium, europium and zirconium. The elements caesium and antimony evaporate during the smelting process and get filtered out of the exhaust gas.

The separated slag which, as already mentioned, contains the radioactive elements or fission products is, as likewise already mentioned, processed into a product which is capable of final storage and can be filled into containers which may be produced out of the decontaminated iron or steel.

Claims

1. A method of decontamination of radioactively contaminated scrap iron and/or steel by smelting the scrap in the presence of slagging agents for the iron/steel smelting, wherein inactive isotopes of the radioactive elements present in the melt are added in addition and subjected to the smelting process.

2. A method as in claim 1, wherein the inactive isotopes are put into the melt.

3. A method as in claim 1 or 2, wherein the inactive isotopes are added in the form of minerals.

4. A method as in any one of the preceding claims, wherein inactive isotopes of the elements strontium, barium, cerium, europium and zirconium are added.

5. A method of decontamination of radioactively contaminated scrap iron according to claim 1, substantially as described herein.

6. Scrap iron andior steel which has been decontaminated by the method of any one of the preceding claims.

7. The employment of decontaminated iron and/or steel produced according to the method as in any one of claims 1 to 5, for the production of containers for the storage of radioactive refuse.