FI85923B - ABSORBATOR FOER NUCLEAR STRAOLNING. - Google Patents

Abstract

1. An absorber for nuclear radiations characterised in that it is formed by an alloy of gadolinium with an aluminium selected from the group comprising pure aluminium, alloyed aluminium and pure or alloyed aluminium containing a dispersed phase.

Description

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Nuclear absorber

The present invention relates to a nuclear radiation absorber.

With the development of nuclear technology, numerous studies have been conducted around the world to design and manufacture efficient and competitive nuclear radiation absorbers. To achieve this objective, the materials used in their manufacture must meet the following criteria: - they must have specific properties suitable for nuclear technology: a large effective capture cross-section, a small se- ·. *: kundar emission, good radiation stability over time. they must have a high melting point in order to withstand well the absorption of radiation, in particular nuclear radiation; - they must conduct heat well so that the calories generated are removed quickly, - their mechanical properties must be such that they can be easily molded, - they must be able to withstand corrosion caused by the weather or the working environment, - they must be as inexpensive as possible.

. ···. Of all the substances used to absorb neutrons, the best known are cadmium, samarium, europium, boron and gadolinium.

The disadvantage of cadmium is that it is a highly toxic substance and that its melting point (321 ° C) and boiling point (765 ° C) are low. Samarium and europium have hardly been used in industry due to their high price.

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The most widely used of these is boron, which is used in various forms: elemental boron, borides, boron carbide, boric acid, etc. Many patent applications have otherwise been filed in this regard. However, this material has very poor mechanical properties and has to be heavily diluted in a metal substrate such as aluminum to provide the necessary properties to mold each type of absorber. But in this way its absorbency is greatly reduced and it has to be compensated by increasing the volume of material used, which in the end significantly increases the cost of the absorber. In any case, when the boron is practically insoluble in aluminum, the substance obtained is a composite product which has to be manufactured using quite complex methods if the boron is to be evenly distributed on the aluminum substrate and uneven absorbency is to be avoided.

Gadolinium and its oxide have been used for many years in various nuclear installations where they, when mixed with fuel, act as a retarder. But using them to build radiation absorbers creates problems.

The oxide, which is generally available as a powder, has to be mixed with other substances using very complex methods, and its very poor mechanical properties make it both cumbersome and expensive to use in the manufacture of complex absorbers.

In addition, this oxide conducts heat poorly and has a relatively poor absorption capacity compared to the absorption capacity of elemental gadolinium.

I .. * The price of this metal itself is high and difficult to use due to its high sensitivity to oxidation.

: **: However, in the slow neutron spectrum, gadolinium has the largest effective capture cross-section of all known absorbents. Compared to boron in particular, 3 85923 has a capture area of 100 times that of thermal neutrons with an energy of 10’2 eV. When it comes to fast neutrons, its power is as good as that of boron.

Therefore, in view of the advantage of gadolinium, but also of its disadvantages, the applicant has studied the matter and devised a means by which it can be used to make inexpensive nuclear radiation absorbers.

This absorber is characterized in that it consists of gadolinium with an alloyed aluminum selected from the group consisting of pure aluminum, aluminum alloys and pure and alloyed aluminum containing a dispersed phase.

It is thus a mixture of gadolinium and aluminum in which the amount of gadolinium is between 0.05 and 70% by weight. If its amount is less than 0.05%, the absorption effect proves to be too small, and when more than 70% is used, difficulties arise in the preparation of the mixture. Preferably, this fork is in the range of 0.1-15% and depends on the quality and flux of the radiation absorbed.

The aluminum used can be pure, whether it has been refined by any means such as three-layer electrolysis or fractional crystallization, or simply recovered from an electrolysis tank with conventional impurities such as iron and silicon.

But this aluminum can also be a conventional alloy, such as 1000, 5000 and 6000 according to the standard of the Aluminum Association, in which case the mechanical properties of the absorbers produced are strengthened, or even aluminum alloyed with at least one other absorbent metal, such as cadmium. , samarium, europium, lithium, hafnium, tantalum, the latter 4 85923 alloys of which can also be obtained from alloy types 1000, 5000 and 6000.

In addition, aluminum, alloyed or non-alloyed, may contain a dispersed phase, such as carbon fibers or the like, to enhance the mechanical strength of the absorbers, or in combination with or separately from these fibers, a radiation absorbing agent such as boron and its derivatives, which may be not more than 30% by weight of the aluminum used.

Due to their good mechanical properties, gadolinium-aluminum alloys prepared in this way can be easily processed into impregnators of any shape by at least one of the following manufacturing methods: sand or die casting by low pressure or high pressure casting, hot or cold rolling, extrusion and forging.

From these mixtures, completely homogeneous structures are obtained in which the effective capture cross-sections are very smooth. In addition, their density, which varies depending on the percentage of Gd, is obtained, up to a Gd content of 30% by weight, close to the density of aluminum, so that very light neutron walls can be produced. Table I gives the density values for two Al-Gd mixtures containing only two substances, one containing 11% Gd and the other 25% Gd.

Table I; Densities of Al-Gd mixtures containing two substances

% By weight of Gd Density IL 2.92 25 3.12 5 85923

The aluminum substrate gives the finished products excellent thermal conductivity (120-180 W / m ° K2 depending on the aluminum substrate chosen), so that the heat generated by the absorption can be quickly removed to the external cooling circuits ·

The initial melting point of the Al-Gd alloys tested is very high, in most cases above 620 ° C; thanks to this property, the neutron barriers made in this way easily withstand the heat generated by the absorption of neutrons or other radiation.

When the atomic weight of Gd is very high (156.9 g), especially the R and X rays are strongly absorbed.

Corrosion resistance is generally unaffected or only slightly affected by the presence of gadolinium, and the corrosion resistance properties are close to those of the aluminum substrates used. The 1000, 5000 and 6000 series alloys have excellent resistance to corrosion caused by weather or marine climate. This durability can be further improved by treating the surface in a suitable manner (coating with an oxide film, alodinizing, painting, coating with plastic, etc.).

The mechanical properties are good and they depend on the selected aluminum substrate. In the case of aluminum-gadolinium alloys containing only two substances, the mechanical properties vary depending on the gadolinium content; Table II gives the results obtained from the cast mixtures, one containing 12% by weight of Gd and the other 25%.

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Table II; Mechanical properties of Al-Gd mixtures containing two substances

Weight% Gd: a Rm MPA Rp 0.2 MPA A% HB

12% 1.40 60 17 40 25% 80 55 0.8 54

Table III shows the results obtained from rolled alloys with a Gd content of 11% by weight.

Table III: Mechanical tensile properties measured from rolled Al-Gd alloy

Weight% Longitudinal Longitudinal

Gd: vice versa. in the direction of

Rm Rp 0.2 A% Rm Rp0.2A% HB

MPA MPA MPA MPA

11 130 110 15 130 110 10 42 By using aluminum substrates to which elements such as copper, silicon, zinc, magnesium, etc. have been added, the strength and elastic limit can be greatly increased, giving the following values:

Rm 280 - 320 MPA

Rp 0.2 220 - 260 MPA

A% 3 - 10%.

The above higher values are not limiting, as it is clear that gadolinium mixtures containing three, four, five, etc. substances could give much higher values than the 7 85923 mentioned above.

The machining of these alloys does not present any difficulty, as the parameters and working speeds to be considered are the same as those normally used for aluminum alloys.

The applications of this invention are diverse and apply to all fields in which radiation absorption is involved (neutrons, rays, X-rays, whether military or civilian).

Examples of applications are: nuclear waste transport and storage baskets, nuclear reactor fuel cell storage basin racks, purification plant protection, military vehicle armor, nuclear fall protection, nuclear reactor elements, protection of control equipment using radiation or radioactive sources, etc.

Claims (11)

Nuclear radiation absorber, characterized in that it consists of an alloy of gadolinium with aluminum selected from the group comprising pure aluminum, aluminum alloys and pure or alloy aluminum containing a dispersed phase. Absorber according to claim 1, characterized in that the proportion of gadolinium is 0.05-70% by weight. Absorber according to claim 2, characterized in that the proportion of gadolinium is 0.1-15%. Absorber according to claim 1, characterized in that the alloy aluminum is selected from the alloys designated by the numbers 1000, 5000 and 6000 according to the standards of the Aluminum Association. An absorber according to claim 1, characterized in that the alloyed aluminum contains at least one metal which is a nuclear radiation absorber. Absorber according to Claim 5, characterized in that the metal belongs to the group consisting of cadmium, samarium, europium, lithium, hafnium and tantalum. An absorber according to claim 1, characterized in that the dispersed phase contains at least one product which is a nuclear radiation absorber. 10 85923 8. Absorber according to claim 7, characterized in that the dispersed phase is boron or a derivative thereof. 9. Absorbent according to claim 8, characterized in that boron represents up to 30% by weight of the aluminum. An absorber according to claim 1, characterized in that the dispersed phase is constituted by fibers. Absorber according to claim 1, characterized in that it is manufactured by at least one of the following manufacturing processes: casting, rolling, extrusion and forging. ! ! ί