GB2038357A - Granulated Ferrous Boron Containing Metal and its Use for Producing Concrete for Protection Against Nuclear Radiation - Google Patents

Abstract

A granular ferrous metal which may be a cast iron, contains 0.1 to 5% by weight of boron, and may be produced by introducing a boron- containing material, such as a boron- containing ore, into a ferrous melt contained in a cupola, and producing granular material from the melt. The granular material is useful as an addition to concrete which is to be used as radiation shielding.

Description

SPECIFICATION Boron Containing Granulated Ferrous Metal and its Use for Producing Concrete for Protection Against Nuclear Radiation This invention relates to boron containing granulated metal. The invention also relates to a process for manufacturing such granulated metal.

The invention is further concerned with the application of such granulated metal to the production of concrete for protection against nuclear radiation.

As is known the growing need for energy has caused rapid development of nuclear power stations. This call for nuclear energy has necessitated simultaneous development of protective techniques against radiation dangerous to humans, notably gamma radiation and secondary neutron radiation.

In order to isolate fissile materials there is used, in the production of such stations or in storing radioactive matter, materials capable of absorbing radiation, firstly heavy metals, then concrete in order to benefit from the considerable mechanical resistance of the latter allied to its specific properties of radiation absorption.

In order to increase its screening qualities against gamma radiation and neutron radiation it is necessary to increase its density, notably by loading it with metallic scraps or chips or "swarf" in association with different heavy compositions such as barytes, magnetite and in certain cases limanite.

In order to increase the capture of neutrons it has also been proposed to use very dense concretes produced by associating with the incorporated swarf compositions having effective large surfaces, notably boron ores containing if possible water (e.g. colemanite, pandermite or borocalcite).

Thus, for example, there has already been incorporated with concrete swarf, granulated iron, and an ore containing boron (particularly colemanite) and a quantity corresponding to about 1% pure boron based on the total weight of the concrete. In certain cases only granulated iron and a boron-containing ore are used.

It is known that the addition of boron compositions to concrete presents certain drawbacks: on the one hand, the setting values ot cement are altered and, on the other hand, the density of the concrete is insufficiently high due to the very low density of boron ores compared with swarf. Moreover, when concrete is set under vibration, the lighter elements which it contains, and in consequence the boron compositions, tend to move up the mass thus leadirig to the heterogenous structure. Finally the addition of different kinds of materials to cement increases its costs of manufacture due to the fact that there is an increase in storage vessels and handling operations (French Patent No. 1,458,833).

The invention proposes an addition for concrete which, by itself, provides a high density characteristic to retard gamma radiation combined with an effectively large area adapted to trap thermal neutrons.

A first aspect of the invention is a granular ferrous metal, preferably a cast iron, which contains about 0.1 to 5% by weight of boron.

The invention also envisages the addition of such a metal to concrete for absorbing nuclear radiation.

The invention also includes a process for manufacturing such a metal characterised in that the metal is prepared in a cupola under known conditions and a boron composition preferably in the form of an ore containing boron is injected into the cupola.

By a granular cast iron there is meant in the terms of the invention any granulated ferrous metal containing at the most 4% by weight of carbon.

Preferably, the granulated metal according to the invention will be constituted by a mixture of granules of different sizes in order to fill the voids to produce the required density.

More precisely, the granulated metal is divided according to normal screening Afnor Nos. 38 to 17 corresponding to diameters of 5 mm,. to 0.040 mm. and to numbers of granular compositions from 0 to 100. The granules will be round or pulverised to satisfy the granularity requirements.

Depending on the compactness desired there can be formed a granular composition with different proportions by weight of grains of different sizes as is known in the art, either for example with two numbers 0-1 6, or three numbers 0-16-50, or all inclusive 0-100, or even four numbers 0--166-550-100.

The granulated metal according to the invention may have, for example the following composition of different elements (% by weight) carbon 0.1 to 4% silicium 0.2 to 2% phosphorus 0.05 to 1% manganese 0.1 to 1% sulphur 0.05 to 1% boron 0.1 to 5% It will be noted that in engineering, the incorporation of boron into iron-bearing granulated metal is already known but for a different object (the reduction of the hardening capacity) and in very small proportions (of the order of a few parts per million).

Also, as is described above, the base composition of such granulated metal is prepared in a cupola, by known methods, by the injection into the cupola of a boron compound, preferably a mineral ore containing boron.

Mineral ores such as colemanite, pandermite or borocalcite or others, containing 40% of 50% of boron oxide, are injected into the cupola through the tuyeres, either in the air-blast canals common to all tuyeres or directly in one or more tuyeres. For this purpose, one can utilise injection apparatus supplied with compressed air of adjustable pressure which propels the mineral ore either in powdered or ganulated form.

In this manner, in order to attain for example a percentage of 1% boron in the metal which will constitute the granulated metal, one adds to the batches close to 75 kg. of colemanite containing 13.6% of boron per tonne.

This procedure permits the injection of a known quantity of material in such an area of the furnace that the yield of the operation stays advantageous. In effect, an addition down the throat of the furnace entails an important loss in the fumes and gases and an addition through the channel or by a ladle gives a very high irregularity in the percentage of boron contained and in the appearance of slag, which is difficult to eliminate and which pollutes the product.

In the method according to the invention, one can naturally use a boron compound other than a mineral ore, for example a ferro-boron. Such alloys are always of a high cost, which makes their use prohibitive either in the cupoia or in the course of fusion in an ore furnace or after such fusion.

The manufacture of the said granulated metal proper, by the pulverisation of the cast metal, is carried out in known manner, such that it is necessary to make a range of sizes sufficiently large and in equal quantities in order to satisfy the required granulometric and density requirements.

The adjustment of the final granulometry can be made by sorting out of the round granules and selection of those that are left, with the addition at the same time of the crushed granules, these operations being known in the art.

The incorporation of granulated metal according to the invention into concrete for employment in applications requiring protection against nuclear radiation either in nuclear reactors, or in storage vessels for radioactive materials is accomplished in such quantities such that the concrete thus manufactured has a density of the order of 5.3 to 6.

It is possible, for example, to manufacture a concrete having a total dry density of 5.95 using the following composition: cement: 350 kg four grades granulated metal (0, 16, 50, 1000): 5530 kg water: 1 50 kg In a further example, a concrete for protection against nuclear radiation of total dry density equal to 5.3 is prepared in a known manner by mixing the following ingredients: cement: 400 kg boron ore (colemite): 400 kg granulated metal: 1 500 kg swarf: 3000 kg water: 1 50 kg The granulated metal according to the invention thus allows the diminution of the number of ingredients used in the manufacture of a concrete or mortar for absorbing nuclear radiation, as well as the reduction of the number of handling operations and storage vessels required, which permits the appreciable lowering of the cost of such concrete.

Claims (13)

Claims

1. Granulated ferrous metal which contains about 0.1 to 5% by weight of boron.

2. Granulated ferrous metal according to claim 1 which comprises, in % by weight, the following elements: carbon 0.1 to 4% silicium 0.2 to 2% phosphorus 0.05 to 1% manganese 0.1 to 1% sulphur 0.05 to 1% boron 0.1 to 5%

3. A process for manufacturing a granulated metal according to claim 1 or 2 where a boron containing material is added to molten ferrous metal in a cupola, and granulated metal is produced from the melt.

4. A process as claimed in claim 3 wherein the boron containing material is a boron containing ore.

5. A process as claimed in claim 4 wherein the ore is selected from colemanite, pandermite and borocalcite.

6. A process according to any of claims 3 to 5 in which the boron containing material is injected into the pipes of the cupola.

7. A method of producing concrete comprising using a granulated metal as claimed in claim 1 or 2 as an additive in the preparation of the concrete.

8. A method as claimed in claim 7 wherein the concrete is a high density concrete.

9. Concrete obtained by the method of claim 7 or 8 and having a density of 5.3 to 6.

10. A boron-containing granulated ferrous metal substantially as hereinbefore described.

11. A process for producing a boron-containing granulated ferrous metal substantially as hereinbefore described.

12. A process for producing concrete incorporating a boron-containing granulated ferrous metal substantially as hereinbefore described.

13. Concrete incorporating a boron-containing granulated ferrous metal substantially as hereinbefore described.