PT82958B - NUCLEAR RADIACOID ABSORBING MANUFACTURING PROCESS - 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

NUCLEAR RADIATION ABSORBER

The present invention relates to a nuclear radiation absorber.

With the development of nuclear techniques, numerous researches have been done, all over the world, to design and manufacture radiation absorbers, effective and competitive. In order to achieve this objective, it is necessary that the materials used to make them meet the following criteria:

- have particular nuclear properties: large effective collection section, reduced secondary emission, good stability over time with respect to radiation;

- have a high melting point to withstand the heat generated by the absorption of radiation, in particular neutron radiation;

- are good conductors of heat to ensure a quick evacuation of the calories produced;

- have mechanical characteristics that allow easy conformation;

resist corrosion in the atmosphere or in the work environment;

- have the lowest possible cost.

Among all the materials used to absorb neutrons, the best known are cadmium, samarium,

cadmium has the drawback of being a very typical product, boron and gadolinium.

mexico and have a very low melting temperature (321 ° C) and boiling temperature (765 ° C). Samarium and Europeans have practically not given rise to industrial development, due to their very high price, most widespread among them is boron, which is used in different forms: elemental boron, borides, boron carbide, boric acid, etc,. In fact, numerous patents related to it have been filed. However, this material pos. it has very poor mechanical properties and must be strongly diluted in a metallic matrix, such as aluminum, for example, to acquire the qualities necessary to be able to take the required shape for each type of absorber. However, its absorption power is greatly reduced and must be compensated by an increase in the volume of material used, which definitely increases the price of the absorber. Anyway, since boron is practically insoluble in aluminum, the material obtained is a composite product whose realization requires the use of very elaborate manufacturing processes, if it is desired to obtain a regular dispersion of boron in the aluminum matrix and to avoid a heterogeneous capacity absorption.

gadolinium and its oxide have been used for many years in several nuclear installations where, mixed with the fuel, they act as moderators. However, its application in the manufacture of radiation absorbers presents problems.

With regard to oxide, which is generally available in powder form, it must be mixed with other products, using

using very complex technologies, and their very bad mechanical properties, make their application, when making absorbers in a complex way, at the same time delicate and expensive. In addition, this oxide has poor thermal conductivity and its absorption capacity is relatively reduced in relation to that of elementary gadolinium.

As for the metal itself, its price remains high and its application difficult, due to its high susceptibility to oxidation.

However, gadolinium has, in the slow neutron spectrum, the highest effective capture section of all known absorbers. Namely, compared to that of boron, its section for thermal energy neutrons 10 eV is 100 times larger. As for fast neutrons, their effectiveness is as good as that of boron.

That is why the applicant, aware of gadolinium's interest, but also of its inconveniences, sought and found the means to manufacture interesting nuclear radiation absorbers from it.

These absorbers are characterized by being made up of a gadolinium alloy with an aluminum chosen from the group comprising pure aluminum, aluminum with alloy, pure aluminum or with alloy containing a dispersed phase.

It is, therefore, an alloy based on gadolinium and aluminum in which the proportion of gadolinium is between 0.05% and 70% by weight. Below 0.05% The absorbent effect is shown to be very low and above 70% difficulties arise in the preparation of the alloy. Preferably, this range is between 0.1% and 15% and depends on the nature and flow of radiation to be absorbed.

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Aluminum used can be pure, either because it has been refined by any means, such as electrolysis of three

layers, or by fractional crystallization, or simply as it was collected from the electrolysis vats, with the usual impurities, such as iron and silicon.

But this aluminum can also be a classic alloy, such as those designated by numbers 1000, 5000 and 6000 in the rules of the Aluminum Association, which allows to reinforce the mechanical properties of the absorbers obtained, or even an aluminum alloy with at least one another metal which also has absorbent properties, such as cadmium, samarium, europium, lithium, hafnium, tantalum, the latter alloys being also obtained from the alloy of types 1000,

5000 and 6000.

In addition, aluminum, whether alloyed or not, may contain a dispersed phase, such as carbon fibers or others, designed to reinforce the mechanical behavior of absorbers, or even, combined or not with these fibers, a radiation absorbing product such as such as, for example, boron and its derivatives, which can represent up to 30% of the mass of aluminum used.

The gadolinium-aluminum alloys thus made allow, due to their good mechanical properties, to be easily transformed into absorbers of any shape, by at least one of the manufacturing processes chosen between molding, either in sand or in molds, low or high pressure, hot or cold rolling, extrusion and forging.

These alloys give rise to perfectly homogeneous structures with very regular effective cross-sections. Beyond

In addition, its density, which is variable as a function of Gd, gives Gd levels up to 30% by weight, a value close to aluminum, which allows the realization of very light neutron barriers. Table I gives density values

de for two binary Al-Gd alloys, one with 11% Gd and the other with 23% Gd.

TABLE I:

BINARY DIGITAL DENSITY Al-Gd Weight% of Gd

Density

2.92

3.12

The aluminum matrix gives the finished products excellent thermal conductivity (from 120 to 180 W / m K ^, according to the chosen aluminum matrix), thus allowing the heat generated by absorption to be quickly evacuated to external refrigeration systems.

melting point of the tested Al-Gd alloys is very high, in most cases above 620 ° C; this characteristic allows the neutron barriers thus manufactured to easily withstand the heating caused by the absorption of neutrons or other radiation.

The atomic mass of Gd is very high (156.9 g), so that rays and X-rays in particular are very absorbed.

Corrosion resistance, in general, is not

Λ Z or e little affected by the presence of gadolinium, and the corrosion characteristics are close to those of the aluminum matrices used. The 1000, 5000 and 6000 series alloys feature a

-6 excellent behavior against corrosion against atmospheric agents or in the marine atmosphere. This behavior can also: be improved by appropriate surface treatments (anodizing, alodino, painting, plastic coatings, etc.).

The mechanical characteristics are high and are a function of the chosen aluminum matrix. In the case of binary aluminum-gadolinium alloys, the mechanical properties vary with the gadolinium content; Table II gives results obtained in cast alloys, one with a Gd content of 12% by weight and the other with a weight percentage of 25%.

TABLE II - BINARY DIGITAL MECHANICAL PROPERTIES Al-Gd

Weight% of Gd Rm MPA Rp 0.2 MPA THE % HB 12% 140 60 17 40 25% 80 55 0.8 54

Table III shows the results obtained in rolled alloys with 11% Gd by weight.

TABLE III - MECHANICAL CHARACTERISTICS OF TRACTION IN DIGA Al-Gd

Weight% of Gd Longitudinal direction Sentic transversal .ongitudinal HB Rm MPA Rp 0.2 MPA THE% Rm MPA. Rp 0.2 MPA THE% • 11 130 110 15 130 110 10 42

Using aluminum matrices with controlled impurities of elements such as copper, silicon, zinc, magnesium, etc.,

increased to achieve the following values:

Rm 280 to 320 MPA Rp 0.2 220 to 260 MPA THE % 3 to 10%

The upper values indicated above are not limiting, it being clear that compositions of ternary, quaternary, quinary alloys, etc., with gadolinium, could not provide values much higher than these.

The machining of these metal alloys does not pose any problems, the parameters and working speeds being taken into account the same ones that are generally used for aluminum alloys.

The applications of the present invention are multiple and cover all areas in which the problem of radiation absorption (neutrons, gamma rays, X-rays) is posed, whether these domains are military or civilian.

Examples of applications include: the baskets for transporting and storing nuclear waste, the frames of swimming pools for the storage of elements with nuclear reactor fuels, the decontamination installation shield, the shielding of military vehicles, anti-atomic shelters, elements of nuclear reactors, the shielding of control devices that use radiation or radioactive sources, etc. This list is by no means exhaustive.

Claims (11)

1.- Nuclear radiation absorber, characterized by being made of a gadolinium alloy with chosen aluminum, in the group comprising pure aluminum, alloyed aluminum, pure or alloyed aluminum containing a dispersed phase. 2. An absorber according to claim 1, characterized in that the proportion of gadolinium is between 0.05% and 70% by weight. 3. An absorber according to claim 2, characterized in that the proportion of gadolinium is between 0.1 and 15%. 4. - Absorber according to claim 1, characterized in that the alloyed aluminum is chosen from the alloys designated by numbers 1000, 5000 and 6000 in the rules of the Aluminum Association. 5. An absorber according to claim 1, characterized in that the alloyed aluminum contains at least one nuclear radiation-absorbing metal. 6. - Absorber according to claim 5, characterized in that the metal belongs to the group consisting of cadmium, samarium, europium, lithium, hafnium, tantalum. 7. An absorber according to claim 1, characterized in that the dispersed phase contains at least one nuclear radiation absorbing product. 8, - Bite absorber with claim as the dispersed phase consists of boron and its derivatives. 9.- Absorber according to claim 8, characterized in that boron represents up to 30%, by weight, of aluminum. 10. An absorber according to claim 1, characterized in that the dispersed phase is in the form of fibers, 11. An absorber according to claim 1, characterized in that it is obtained according to at least one of the manufacturing processes chosen from molding, rolling, extrusion and forging.