Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium
  • C22C23/06—Alloys based on magnesium with a rare earth metal as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C49/00—Alloys containing metallic or non-metallic fibres or filaments
  • C22C49/02—Alloys containing metallic or non-metallic fibres or filaments characterised by the matrix material
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F1/00—Shielding characterised by the composition of the materials
  • G21F1/02—Selection of uniform shielding materials

Definitions

• the present invention relates to metal absorbers of nuclear radiation. It more particularly relates to metallic nuclear radiation absorbers containing metallic samarium in the form of metallic alloy chosen from at least one of the families of copper-samarium, aluminum-samarium and magnesium-samarium alloys, respectively, each of said families of alloys containing from 0.05 to 95% by weight of samarium relative to the total weight of the alloy.
• the absorption materials must meet the following criteria: - firstly, having specific nuclear properties: large cross section of neutron capture, low emission of secondary radiation, good stability over time with respect to radiation; - have a high melting point to withstand the heating generated by the absorption of radiation, and in particular neutron fluxes; - be a good conductor of heat to facilitate cooling to the outside; - not too high residual heat (released as radiation after stopping); - sufficiently high mechanical resistance; - resistance to corrosion with respect to the refrigerant, or in the working atmosphere; - have good stability with respect to heat and radiation; - competitive cost, both in terms of raw material and in implementation.
• All the elements absorb more or less nuclear radiation, but those which have the most striking neutron-absorbing properties are: cadmium, boron, europium, hafnium, gadolinium, samarium and dysprosium.
• Europium and dysprosium although having a large effective cross-section, give rise to very limited applications, given their very high price.
• Gadolinium has the highest cross-sectional area of all known absorbers in the thermal neutron spectrum. It can be observed that for example for neutrons of initial energy from 10 ⁇ 1 to 10 ⁇ 3 Electronvolts, its effective capture section is approximately 100 times higher than that of boron. Unfortunately, in the area of epithermal neutrons and slow neutrons (energy from 0.3 to 102 Electronvolts, the absorption properties are very reduced compared to boron.
• boron which is used in different forms: elemental boron, borides, boron carbide, boric acid, oxide, nitride, etc. and many patents have been filed.
• boron-based materials are delicate: elemental boron has poor mechanical properties, it is highly oxidizable at high temperature and its corrosion resistance is poor; it must then be inserted in the form of chemical compounds defined in various matrices, and these composite materials pose problems of homogeneity and are difficult to use.
• Hafnium has much lower absorption properties than boron for thermal and epithermal neutrons, its cost is high and it is difficult to use because of its oxidability.
• the samarium compared to all the elements mentioned above, has extreme neutron-absorbing properties interesting, intermediate between boron and gadolinium for thermal neutrons, superior to boron and gadolinium for intermediate and fast neutrons; two resonance zones give only two weaknesses for the samarium compared to boron, the first between 1 and 5 eV of neutron energy, and the second between 30 and 40 eV, but these weaknesses can be compensated by the quantity of elements neutrophages introduced into the final alloy. Compared to gadolinium, it is perfectly clear that the samarium is more interesting overall on the whole spectrum of energy of neutrons.
• These new absorbers are characterized by the fact that they essentially constitute three families of alloys, one family having as base metal aluminum, another family having as base metal copper, and a third having as base metal the magnesium.
• These three families of new alloys generally present complementary interests. Indeed, aluminum is very light but has fairly low mechanical properties above 300 ° C. In comparison, copper is heavier, but has a higher thermal conductivity than aluminum (which is already excellent) and gives high mechanical properties up to 500 ° C. Magnesium will give rise to the lightest alloys, but its resistance to corrosion is low, and its thermal conductivity lower than that of aluminum. In these three families, the absorption properties of nuclear radiation are given by the relative mass of samarium present in the metal matrices concerned.
• the absorption coefficient of the alloy is directly a function of the weight percentage of this element in the alloy.
• the absorption coefficient will be directly a function of the percentage by weight of samarium.
• the alloys of the Cu-Sm family will be situated in a range of 0.05% to 50% of Sm, or in a range of 70% to 90% Sm.
• the alloys of the Al-Sm family it will preferably be situated in a range of 0.05% to 25% by weight of Sm, and for the Mg-Sm family, in a range of 0.05 to 55%.
• the aluminum, copper and magnesium used can be pure, or alloyed with any other addition element which will make it possible to reinforce the mechanical properties of the absorbers or to modify their technological properties (ease of implementation, resistance corrosion, machinability, weldability ).
• addition elements other than aluminum, copper, magnesium and samarium other neutron-absorbing elements can be added such as gadolinium, europium, hafnium, boron (in phase dispersed or not), cadmium, lithium, dysprosium, etc. where fibers can be inserted (alumina, silicon carbide, boron, carbon ).
• the aluminum-samarium, or copper-samarium, or magnesium-samarium alloys exhibit very good ease of implementation by at least one of the manufacturing processes chosen from molding, whether in sand, in shell, under high or low pressure, hot or cold rolling, extrusion, forging, vacuum forming ...
• the thermal conductivity of the final absorbent metallic material will strongly depend on the mixture selected (Al-Sm, Cu-Sm or Mg-Sm) and possibly on other addition elements introduced into the alloys to improve their mechanical, technological or absorption.
• an Al-Sm alloy with 10% Sm will have a thermal conductivity of 150 W / m ° K
• an Al-Si-Sm alloy with 7% silicon and 2% samarium the same thing
• a Cu-Sm alloy with 4% of Sm will show a thermal conductivity of 250 W / m ° K approximately.
• This notion of thermal conductivity is important and will strongly influence the choice of the optimal composition sought for the absorbent material, because any absorption of radiation (and especially neutron capture) is accompanied by a release of heat which must be removed from the hot parts to cold parts as quickly as possible. It will be noted that the aluminum and copper matrices are from this point of view very well placed.
• the starting points of melting of the alloys Al-Sm, Cu-Sm, Mg-Sm are high, which gives them very good stability at high temperature, and which allows them to withstand without problem the heating caused by absorption of neutrons or other radiation.
• the solidification interval varies according to the chemical composition and Table II indicates some values of alloys studied.
• Corrosion resistance in general, is not or little affected by the presence of samarium for contents less than 25% by weight, and the corrosion properties will essentially depend on the nature of the aluminum, copper matrices and magnesium used.
• aluminum for example, aluminum-silicon matrices (7 to 10% of Si) and aluminum-magnesium will exhibit good corrosion resistance against atmospheric agents, against demineralized water at 50 ° C or in a marine atmosphere. This behavior could be further improved by appropriate surface treatments (anodization, alodine, paints, plastic coatings ).
• the corrosion resistance is practically not affected by the presence of the samarium. This corrosion resistance can be further improved by additions of chromium, nickel, aluminum, tin ...
• the corrosion resistance will generally be low, and the use of these will be reserved for applications in a non-corrosive environment.
• Radiation absorbers must have high mechanical properties and be as stable as possible at high temperatures. To do this, and depending on the specifications imposed, a judicious choice of the Al-Sm, Cu-Sm and Mg-Sm alloys and their additional addition elements will be made. The right compromise will have to be found not only based on mechanical characteristics nics, but also depending on the thermal conductivity of the weight, the nuclear characteristics, the possibilities of implementation. As an example, we will see in the following tables the results of mechanical tests on different Al-Sm and Cu-Sm alloys.
• magnesium-samarium alloys are somewhat special; copper and aluminum do not dissolve samarias in the solid state.
• magnesium can dissolve up to 12% of samarium at around 550 ° C, and this solidity is no more than 2 or 3% at room temperature: this characteristic shows a possibility of structural hardening by quenching and tempering on these binary alloys.
• Examples of applications include: baskets for transporting and storing nuclear waste, pool racks for storing fuel elements from nuclear reactors, shielding decontamination facilities, atomic and nuclear protections in general, nuclear reactor components, shielding of control devices using radiation or radioactive sources, shielding of electronic boxes, etc.
• the metals placed in the crucible are heated for 1 hour at 1200 ° C, then the resulting mixture is maintained for 1 hour at 1100 ° C in order to obtain a perfectly homogeneous liquid mass.
• the oven is then opened, the top of the crucible stripped of its encrustations and its contents poured into a mold such as an ingot mold, which can be cooled with water.
• the metal mass is first brought to 660 ° C to melt the aluminum, then brought to 1100 ° C for about 1 hour.
• the samarium gradually dissolves in liquid aluminum.
• the temperature is reduced to 800 ° C, the oven is opened, the oxides floating on the surface of the liquid eliminated and the contents of the crucible poured into a mold, such as a metal mold, a sand mold, a ceramic mold or an ingot mold.
• the alloy obtained can be put into its final form using the usual transformation techniques, such as machining, forging, lamination or extrusion.

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• High Energy & Nuclear Physics (AREA)
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Cited By (6)

Citations (1)

• 1986
  • 1986-07-30 CH CH305286A patent/CH667881A5/fr not_active IP Right Cessation
• 1987
  • 1987-07-27 EP EP87810422A patent/EP0258178A1/de not_active Withdrawn

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