FR2556876A1 - Process for the manufacture of structures made of composite materials forming a neutron shielding - Google Patents

Abstract

Process for the manufacture of structures made of composite material intended to be used as neutron shielding, consisting in introducing a neutron-absorbing material into at least one of the components of the composite material; the neutron-absorbing material is gadolinium.

Description

 The invention relates to a method of 2bracation of structures made of composite materials forming neutron shielding.

 the mechanical qualities and the low weight of composite materials have led to its use of machines for which weight reduction is a major concern. Composite materials are therefore used for the production of reentry bodies, caps, parts of structures in the space and aeronautical industries.

 Nuclear risks, and in particular the effects of high neutron fluxes, which may be released by atomic explosions and enhanced radiation weapons, on nearby nuclear weapons, on electronic devices and on personnel have prompted manufacturers to protect essential installations, weapons or devices by neutron shielding These shields are formed by a sheet or a dbp8t of a material having a large capture section with respect to the neutrons. The material with the highest capture section is gadolinium, which is widely used in nuclear power for "poisoning" in all cases where there is a risk of criticality, for example in the reprocessing of nuclear fuels.

 The subject of the invention is a method of manufacturing structures made of composite material intended to serve as neutron shielding.

According to the invention, the method consists in introducing a neutron absorbing material into at least one of the components of the composite material.
The explanations given below by way of example will make it possible to understand how the invention can be carried out.

 composite materials generally contain a filler (fibers or particles) coated with "resin".

The defining characteristics of a composite are: -the nature of the fibers or the
charge,
-the nature of the "resin"
coating (phenolic, epoxy ...)
-the properties of the "resin,
-the properties of the filler
(mechanical, thermal,
electric).

Depending on the destination of the structure, the composite material is chosen according to the desired characteristics. Thus, in the case of a reentry body, particular attention will be paid to the ablative properties of the composite (multidirectional or unidirectional matrices) as well as to the refractory and dielectric properties of the filler or fibers used,
These various properties are obtained by loading the composite with nitrides, oxides, silicides, carbides, de-metal or metalloid borides.

So far only the characteristics
mechanical, refractory and dielectric ticks have been developed. This is how composites were obtained whose mechanical characteristics are capable of competing with those of metals by using carbon or boron fibers.

 Or-boron is a neutron absorbing element whose capture section is to twist 4000 barns.

 Owing to the small thickness of the fibers of the boron layer on the support fibers (tungsten or.

graphite) the stopping power of a large neutron flux is low and cannot provide effective protection.

 According to a characteristic of the invention, it is preferred to use gadolinium as a filler material, the capture section of which is of the order of 46,000 barns. However, this is an average value. In fact, isotopic preparation or enrichment techniques would allow, with the isotopes 155 and 157 which are contained respectively at 14.78% and 15.71 in the commercial gadolinium, to obtain significantly higher efficiencies.

 Gadolinium 155 has an absolute section of 56,200 barnsp for the entire neutron spectrum, 70,000 for cell neutrons and gadolinium 157, an absolute section of 242,000 bats 160,000 for cell neutrons.

 The maximum efficiency is found in the development of gadolinium boride where the action of the two components allows a very good effioacity in the whole spectrum of energy of the neutrons.

Fibers of gadolinium oxide and of gadolinium boride have characteristics very similar to those of boron fibers and a very high stopping power with respect to neutrons
Gadolinium as oxide or boride is used, according to the invention, for the manufacture of fibers used in 'composite materials or else incorporated into the matrix in the case of sintered materials.

 The gadolinium compounds obtained in the form of fibers or pulverulent constitute at least part of the charge of resins used for the manufacture of shields for the protection of the personnel and / or the material likely to be subjected to a flux of neutrons.

 The process for manufacturing structures in composite materials forming neutron shielding consists in using a filler in a neutron-absorbing material, the filler being preferably gadolinium or a chemical compound of gadolinium.

 Gadolinium or its chemical compound is deposited in the form of a thin layer by any known means on wires or ribbons. The wires thus treated are used in the manufacture of panels or structures.

Claims (7)

 1. A method of manufacturing structures from composite material intended to serve as neutron shielding, characterized in that it consists in introducing a neutron absorbing material into at least one of the components of the composite material.  2. Method according to claim 1, the composite material comprising fibers coated with resin, characterized in that the neutron absorbing material is deposited in the form of a thin layer on the fibers.  3. Method according to claim 1, the composite material comprises a pulverulent or fibrous filler, characterized in that at least part of the filler consists of a neutron absorbing material.  4. Method according to claim 2 or 3, characterized in that the neutron absorbing material is a simple element or a chemical compound.  5. Method according to revendicatioh 4, characterized in that the neutron absorbing material is natural gadolinium.  6. Method according to claim 5, characterized in that the gadolinium is enriched in one of its isotopes 155 or 157.  7. The method of claim 7, the neutron absorbing material is gadolinium boride.