WO1995030990A1

WO1995030990A1 - Container for absorbing neutron radiation

Info

Publication number: WO1995030990A1
Application number: PCT/DE1995/000570
Authority: WO
Inventors: Karl-Heinz Rudnick; Manfred Tennie; Günter Zeitzschel
Original assignee: Siemens Aktiengesellschaft
Priority date: 1994-05-09
Filing date: 1995-04-27
Publication date: 1995-11-16
Also published as: DE4416362C2; DE4416362A1

Abstract

The container (1) is intended to shield a neutron-emitting object, e.g. a fuel element of a nuclear reactor in a fuel element supporting frame. In order to ensure particularly reliable shielding with, at the same time, a high degree of absorption, the invention proposes the application of a surface coating (4) of a neutron-absorbent material (e.g. boron). Here, a surface coating process known per se is preferably used, e.g. plasma spraying, sputtering or hard soldering. The container (1) with a surface coating (4) applied to e.g. a metal or ceramic substrate (3) is distinguished by a uniform distribution of the neutron-absorbent material over all areas of the container (1) and is particularly easy to process into a wide variety of shapes surrounding the neutron-emitting object.

Description

description

Container for the absorption of neutron radiation

The invention relates to a container for shielding a neutron emitting object.

To achieve a desired neutron absorption, such containers are produced from absorber parts as shafts, canisters or similar configurations which surround the object emitting neutrons. The use of such containers enables e.g. the compact storage of neutron-emitting components from nuclear reactors. For example, from EP 0 385 187 AI a fuel assembly storage rack is known, in the absorber plates in the assembled state a number of

Form shafts that enclose the fuel elements over their entire length. The absorber sheets or absorber parts forming the shafts are made of neutron absorbing material, e.g. made of boron steel or borated sheet.

The absorber parts are usually manufactured in this way. that a certain proportion of e.g. 0.8 wt .-% boron is introduced into a molten base material. An absorber part produced from this melt is then further processed into a shaft, a canister or another container. A disadvantage of this boron enrichment, however, is that the base material becomes brittle through melting or storing over a certain amount of boron, so that further processing is extremely difficult and even impossible in special applications.

Another possibility of producing such an absorber part is to store the neutron absorbing material in a base material, for example made of aluminum or plastic (plastic mat), and then to provide this base material with austenitic sheets on both sides . However, this type of production of the absorber part has the disadvantage that a homogeneous distribution of the boron within the base material is not always guaranteed. However, the requirement for a homogeneous distribution of the neutron-absorbing material in all areas of the absorber part must be strictly observed due to the risk of a criticality accident. This requirement also includes avoiding de-homogenization along the absorber part.

US Pat. No. 4,218,622 describes a composite neutron absorption part which has a thin carrier film or a thin carrier plate to which a polymer matrix is applied, in which boron-carbide particles are embedded. Glass fiber is preferably used as the material of the carrier film or the carrier plate. The boron carbide particles are evenly distributed on the surface of the polymer matrix and a boron concentration of up to 0.1 g / cm ^{2 is} achieved. When the composite absorber part is used in a fuel pool, this absorber part has a thickness of up to 7 mm, is in the form of a film or

Sheets designed and hung between an inner wall and an outer wall. To what extent a homogeneous distribution of the boron carbide particles arranged on the surface of the polymer matrix can be guaranteed over a longer period of time. US Pat. No. 4,218,622, in particular with regard to possible abrasion on the surface, cannot be found. The problem of a homogeneous distribution of neutron absorbing material both in area and in volume also remains with the absorber part mentioned in US Pat. No. 4,218,622.

The invention is therefore based on the object of specifying an absorber container with which, while avoiding the disadvantages set out in the case of an intended use, secure shielding of the object emitting neutrons is ensured with a high degree of absorption in the entire area to be shielded . This object is achieved in that a surface layer containing a neutron absorbing material is applied to a supporting base body of the container.

The surface layer containing the neutron absorbing material is preferably applied to the base body, as a result of which it is possible to achieve both a homogeneous distribution of the neutron absorbing material within a desired layer thickness and an extremely adhesive connection of the surface layer to the material of the base body to reach. This in turn enables a particularly simple manufacture of the container to the desired shape, since the load-bearing parts of the container, which absorb the mechanical loads on the container, can be coated before or after assembly. A complicated structure with several load-bearing parts, between which the absorbent material is embedded, is therefore not necessary. In addition, the coating with a homogeneous distribution of the neutron absorbing material results in a loss of this material, e.g. largely avoided by abrasion on the surface and a de-homogenization. Also commercially available materials or ceramics for the base body, i.e. as the base material. So far this has not been possible.

Boron is preferably used as the neutron absorbing material. The surface layer containing the neutron absorbing material can be applied on the inside and / or on the outside. By applying the

In the case of a crack in one of the surface layers, a secure shielding is guaranteed both on the inside and on the outside, since the crack is shaded by the opposite surface layer with a probability bordering on certainty. The container is preferably an absorber shaft, which is constructed from a base body which is made from one piece, for example cast, or is composed of several parts, in particular metallic or ceramic sheets.

The surface layer is preferably applied by means of a coating process. Such coating processes are e.g. plasma spraying as a thermal spraying process, high-performance cathode sputtering as a vacuum coating process (sputtering) or evaporation or soldering of hard material layers.

Such a container provided with a surface coating of a neutron absorbing material is conveniently, e.g. used within a fuel assembly storage rack, as a container or shaft for a fuel assembly of a nuclear reactor.

An embodiment of the invention is based on a

Drawing explained in more detail. In it show:

1 shows a perspective view of an absorber shaft provided with a surface layer, and

FIG. 2 also shows a perspective view of an absorber shaft according to FIG. 1 made of interconnected absorber sheets.

Corresponding parts are provided with the same reference symbols in both figures.

The absorber shaft 1, which is square in cross section according to FIG. 1, serves to receive a fuel element (not shown). The wall 2 of the absorber shaft 1 is made of one

Base body 3 and a surface layer 4 made of neutron absorbing material, for example boron, applied thereon built up. The surface layer 4 is provided here on the outside of the wall 2. But it can also be applied to the inside of the wall 2. A surface layer 4 can also be applied to both sides of the wall 2.

The surface layer 4 serves for the absorption of neutrons, which are emitted by the fuel element arranged inside the absorber shaft 1 and surrounded by the wall 2 or another object stored there.

In the exemplary embodiment according to FIG. 2, the absorber shaft 1 is constructed from four absorber sheets 5 to 8 interlaced with one another. For this purpose, the absorber sheets 5 to 8 are provided in a manner not shown in detail with slots which extend over part of their length and which engage in one another during assembly.

The absorber sheets 5 to 8 each have - as in the exemplary embodiment according to FIG. 1 - a base body 3 made of a metallic or ceramic material. The basic body 3 of each absorber sheet 5 to 8 is provided on both sides with a surface layer 4 which contains the neutron-absorbing material.

As indicated in FIG. 2, each of the absorber sheets 5 to 8 forms part of the walls 2 of a plurality of adjacent absorber shafts 1. This is indicated in FIG. 2 by areas 9 which extend over the wall 2 of the through the absorber sheets 5 to 8 protruding absorber shaft 1 protrude.

In the manufacture of the absorber parts 2 and 5 to 8 used for the absorber shafts 1, the surface layer 4 is applied to the base body 3 by means of a surface treatment process. This includes plasma spraying, high-performance cathode sputtering and vapor deposition or soldering hard material layers possible surface treatment or coating processes.

That e.g. The plasma spraying process described in the publication "Metallwissenschaft und Technik", 47th century, issue 3, March 1993, pages 230 to 235, is usually used in the fields of wear and corrosion protection and in the production of insulation layers. In this publication, on pages 241 to 244, the coating processes for the same areas of application are also available

High performance cathode sputtering and evaporation described.

Another preferred surface coating method is to solder the surface layer 4 onto the base body 3. Instead of the usual additives or in addition to these additives, boron or another neutron absorbing material is introduced into the solder. This enables the use of a commercially available sheet as the material for the base body 3. The material provided with the neutron absorbing material is soldered onto this sheet. As a result, both a homogeneous distribution within the surface layer 4 and an extremely adhesive connection between the surface layer 4 and the base body 3 are achieved.

Just like plasma spraying or sputtering, brazing is usually used for the production of wear-resistant layers, as described, for example, in the article "Production and properties of wear-resistant layers with the aid of plastic-bonded hard / soldered parts" by H. Krappitz, U. Mürrle and J. Nauber is described in the Degussa brochure with the identification Do 175-1-105-589 DVS. It is common to all of the methods mentioned that a firm, stable metallic or metal-ceramic connection is produced between the base body 3, which can be metallic or ceramic, and the surface layer 4. In addition, the process ensures a homogeneous distribution of boron in the surface layer, both over the surface and the depth.

The container 1, on the base body 3 of which the surface layer 4 containing the neutron absorbing material is applied by one of the surface coating methods mentioned by way of example, can be brought into the desired shape in any manner. Thus, according to the exemplary embodiment according to FIG. 1, the absorber shaft 1 is formed from a single base body 3. In contrast, the absorber part according to the exemplary embodiment according to FIG. 2 consists of a number of absorber plates 5 to 8, from which the absorber shaft 1 is composed.

The absorber part 1 described has the essential advantage over the prior art that it can also meet a requirement for higher absorption rates and thus a higher boron content. This in turn advantageously enables a particularly compact storage of fuel elements in the fuel assembly storage rack. A comparatively higher enrichment of the fuel elements to be stored is also advantageously possible while avoiding the risk of a criticality disturbance.

Claims

1. container (1) for shielding a neutron-emitting object with a supporting base body (3), so that a surface layer (4) is applied to the base body, which contains a neutron-absorbing material.

2. Container (1) according to claim 1, which also means that the neutron-absorbing material is homogeneously distributed in the surface layer.

3. Container (1) according to claim 1 or 2, so that the surface layer (4) containing the neutron absorbing material is applied on the inside and / or on the outside.

4. Container (1) according to one of claims 1 to 3, d a d u r c h g e k e n n z e i c h n e t that the neutron absorbing material is a boron-containing material.

5. A container (1) according to one of claims 1 to 4, that the base body (3) consists of a metallic or ceramic material.

6. Container according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that this is an absorber shaft, which is constructed from a single piece or from sheet metal fastened together.

7. A method for producing a container for shielding a neutron emitting fuel element, characterized in that a Base body (3) of the container (1) is coated with a surface layer (4) which contains a neutron absorbing material, the surface layer (4) using a coating method for producing an adhesive connection between the surface layer (4) and the base body (3), such as thermal spraying (plasma spraying), cathode sputtering (sputtering), evaporation or soldering.

8. Use of a container (1) with a supporting base body (3), on which base body (3) a surface layer (4) is applied, which contains a neutron absorbing material, in a device for storing fuel elements of a nuclear power plant .