IE861851L

IE861851L - Absorber for nuclear radiations

Info

Publication number: IE861851L
Application number: IE861851A
Authority: IE
Original assignee: Montupet Fonderies
Priority date: 1985-07-11
Filing date: 1986-07-10
Publication date: 1987-01-11
Also published as: PT82958B; EP0211779B1; NO862793D0; KR870001611A; GR861792B; DK327786A; PT82958A; ES2001015A6; FI85923C; FR2584852B1; AU6004886A; ATE40763T1; BR8603239A; FR2584852A1; NO169035C; DK327786D0; KR910007461B1; FI85923B; EP0211779A1; IE58952B1

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

58952 The present invention relates to an absorber for nuclear radiations™ With the development in nuclear processes, a great deal of research has been carried out on a world-wide basis, for the purpose 5 of devising arsSproduciog effective and competitive radiation absorbers™ To achieve that aim,,, the materials used for producing than must comply mth the follow-ing criteria: - they must have particular nuclear properties: a large effective capture section, a 1©^ level of secondary emission, and 10 good stability in respect of time with respect to the radiation; - thav must have a high melting point in order to withstand the heating effect generated by the absorption of radiation, in {articular neutron rays;; - they must be good conductors of heat in order to provide 15 for rapid removal of the heat generated; - they must have mechanical characteristics which permit them easily to be shapedj - they must resist corrosion in the atmosphere or in the working medium; and 20 - they must be of the lowest possible cost., Ainong all the materials used for absorbing neutrons f the most widely known are cadmiumP samarium, europium, boron and gadolinium.

Cadmium suffers from the disadvantage of being a highly toxic 25 substance and having a very low melting point v321°C) and a very lew hoil 'rrj point (765°C). Samarium and europium have given rise to pr&eti'eally no industrial development because of their excessively high cost. 15® most widespread among such materials is boron which is used in different forms: elementary borone, boridesf boron carbide, * boric acx<3.£ etc. Moreovere, a large number of patents have been filed an that subject.. However£, this material suffers frc® very 5 poor mechanical properties and it must be highly diluted in a metal matrix such as aluminium for example in order to acquire the qualities necessary for it to be able to assume the form required for each type of absorber. In that case however, its absorption capacity is greatly reduced and must be compensated by an increase 10 in the volume of material used? and thatP in shorte substantially increases the cost of the absorber, At any event,, boron being virtually insoluble in aluminium, the material obtained is a composite productj. and the production thereof makes it necessary to have recourse to highly complicated production processes if regular 15 distribution of the boron in the aluminium matrix is to be achieved and if heterogeneity in the absorption capacity is to be avoided.

Gadolinium and its oxide have already been used for a number of years new, in various nuclear installations in whiche, mixed with the fuel t, they perform the function of moderators. However t, the 20 application thereof to the production of radiation absorbers gives rise to problems„ As regards the oxide ^ which is generally available in powder fornix it must be mixed with other substances, v#hich involves the use of highly complicated technologies, and its very poor mechanical 25 properties make the use thereof for the production of absorbers of complex shape, both a delicate and an expensive matter,, In addition, this oxide suffers from a poor level of thermal conductivity and its absorption capacity is relatively low in comparison with that of elementary gadolinium. 30 As regards the metal itself, the cost hereof is still high and it is difficult to use because of its very high level of oxidizability. - 3 ~ However£. in the spectrum of slew neutrons, gadolinium has the highest effective capture section of all the known absorbers.

In particular £, in comparison with boron,, its section for thermal _*? neutrons of an energy level of 10 ~ eV is one hundred times 5 greater- As regards fast neutrons, its effectiveness in regard thereto is as good as that of boron.

It is for that reason that the present applicantsf being aware of the attraction of gadolinium bat also the disadvantages involved therewith, sought and discovered a %ray of making therefrom 10 attractive nuclear radiation absorbers.

The absorber is characterised in that it is formed by an alloy of gadolinium with an aluminium selected frcm the group comprising pure aluminiumt» allayed alisninium, and pare or alloyed aluminium containing a dispersed phase- 15 This therefore involves an alloy based on gadolinium and aluminium in which the proportion of gadolinium is between 0„0i>% and 70% by weight. Below a value of 0.05%4, the absorption effect is found to be excessively reduced while above a value of 70% s difficulties occur in regard to producing the alloy. Preferably, 20 the above - indicated range is between 0.1 and 15% and depends oo the nature and the flux of radiations to be absorbed, The aluminium used nsay be pore* whether it has bean refined by any method such as three-layer electrolysis or fractional crystallization or is simply such that it is collected at the 25 discharge of electrolysis tanks with its usual impurities such as iron and silicon.

However, the aluminium may also be a conventional alloy such as those denoted by numbers 1000 , 5000 and 6000 in the Aluminium 9 Association standards, which makes it-possible to enhance the ■ j, • mechanical properties of the absorbers produced., or alternatively an - 4 - 5 10 15 20 25 alloy of aluminium with at least one other metal feiiich also has absorbent qualities such as cadmium „ saneriumt, europium, lithium P hafniusn and tantalum^ which latter alloys may also be produced from alloy of types 1CC0,. 5000 ar/3 S0C0* In additiont, the aluminium which may or may rot be alloyed nay contain a dispersed phase such as carbon fibres or other fibres which are intended to enhance the mechanical strength of the absorbers or alternatively, whether combined with such fibres or nott. a product which absorbs radiation such as for example boroo. and its derivatives,, which may represent up to 30% of the mass of aluminium used™ Hie gadolinium-aluminium alloys which are produced in that way,, by virtue of their good mechanical properties,? can be easily transformed into absorbers of any shape whatever by one at least of the production processes selected from casting g whether in sand,, in a chill mould,, or under high or low pressure, hot or cold rollinge extrusion and forging.

Such alloys give perfectly homogenous structures with very regular effective capture sections. In additionr their specific gravity which is variable in dependence on the percentage of Gd gives a value close to that of aluminium,, with proportions of Gd of up to 30% by weight t< which makes it possible to produce very light neutron terriers. Table I below gives values in respect of specific gravity for two binary alloys Al-Gds, one containing 11% of Gd and the other containing 23% of Gd.

TABLE I : SPECIFIC GRAVITIES OF BINARY ALLOYS Al-Gd % by weight of Gd Specific gravity 11 25 2.92 3.12 5 - The aluminium matrix gives the finished products an 2 excellent level of thermal conductivity {fran IX) to 180 W/m depending an the aliminiwn matrix: selected) t9 which thus makes it possible rapidly to rero^e the heat generated by absorption, to 5 external cooling systems- The point at which the alloys Al-Gd begin to melt is very hight, being in most cases higher than 620°Q that characteristic pentiits the neutron barriers which are produced in that ray easily to withstand the heating' effect caused by the absorption of neutrons 10 or other rays.

The atomic mass of Gd being very high (156.9 g), I" and X-rays in particular are absorbed to a very substantial extent.

Resistance to corrosion,, generally speaking,, is not affected or only little affected by the presence of gadolinium, and 15 the corrosion properties are close to those of the aluminium natrices used. Alloys of series 1COO, 5GQ0 and 6000 enjoy excellent resistance to corrosion in respect of atmospheric agents or in a marine atmosphere. That resistance to corrosion may be further enhanced by suitable surface treatments (anodizatian,, alcdinet, painting,, plastics 20 coatings etc-).

The mechanical properties are high and. depend on the aluminium metric selected., In the case of binary alutdnium-gadolitiima alloys, mechanical properties vary with the amount of gadolinium j Table II sets out results obtained with cast alloys 2, one with a 25 proportion of Gd of 12% by weight and the other with a percentage by weight of 25%.

TABLE II - MECHANICAL PROPERTIES OF BINARY Al-Gd ALLOYS % by weight of Gd Rm MPA Bp 0»2 MPA A % HB 12% 140 60 17 40 25% 80 55 0.8 54 Tfeble III sets forth the results obtained with rolled alloys containing 11% fay weight of CM.

MiL/I1. " MERCHANTPAT, TENSILE CHARACTERISTICS IN A ROLLS) Al-Gd ALLOY 1 % by weight of Gd Lengthwise direction Lengthwise transverse direction HB Rm MPA Rp 0.2 MPA A % Rm MPA Rp 0„2 MPA A % 11 130 110 15 130 110 10 42 By using aluminium matrices vmich are doped with elements such as copperL, silicon, zinc, magnesium etc. £. the level of strength and the elastic limit can be greatly increased to attain the following values: Rm 280 to 320 MPA Rp 0„2 220 to 260 MPA A % fran 3 to 10% The higher values set out hereinbefore are not limiting it being appreciated that ternary, quaternary e, quinary,, etc alley carnpositions comprising gadolinium could give values much higher than those indicated above.

Machining of those metal alloys dees not give rise to 5 any problem,, the parameters and the operating speeds to be taken into account being the same as those which are generally used for aluninium alleys™ There are snany uses for this invention and they all concern areas in which there is a problem in regard to the absorption of 10 radiation, (neutrons, ¥-rays. X-rays), whether such areas are military or civil.

The following may be mentioned sn exanples of use: flasks for transporting and storing nuclear waste, swimming-pool racks for storing nuclear reactor fuel elements, decontamination installation 15 shielding, shielding or armouring for military vehicles t, fall-out shelters e, nuclear reactor elegants t, shielding for monitoring apparatuses using radiation or radioactive sources, etc- That list would not be intended in any way to be limitative. * i. ( - 8 -

Claims

1. - An absorber for nuclear radiations w-herein 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.

2. .An absorber according to claim 1 wherein the proportion, of gadolinium is from 0-05% to 70% by weight.

3. An absorber according to claim 2 wherein the proportion of gadolinium is from 0.1 to 15%.

4. An absorber according to claim 1 wherein the alloyed aluminium is selected from the alloys denoted by the numbers 10C0£, 5000 and 6000 in the Alununium Association standards „

5. An absorber according to claijn 1 wherein the alloyed aluminium contains at least one nuclear radiation absorber metal.

6. An absorber according to claim 5 wherein the metal belongs to the group formed by cadmiumt, samariumf, europium, lithium, hafnium and tantalum™

7. An absorber according to claim 1 wherein the dispersed phase contains at least one nuclear radiation absorber product-

8. An absorber according to claim 7 wherein the dispersed phase is formed by boron or one of the derivatives thiereof.

9. An absorber according to claim 8 wherein the boron represents up to 30% by weight of the aluminium-

10. An absorber according to claim 1 wherein the dispersed phase is in the form of fibres.

11. An absorber according to claim 1 wherein it is produced by one at least of the production processes selected from casting,, rolling# extrusion and forging.

12. An absorber for nuclear radiations as claimed in claim 1 substantially as hereinbefore described by way of Example. Dated this 10th day of July 1986- BY: TONKINS & CO™;, Ap^icants Agents, (Signed) j|_ 5 DJftmouth Road, DUBLlM 6. 20 25 30 35 - 10 -