EP0942435B1 - Radiation screening arrangement for radioactive material transport container and method of setting up such a radiation screening arrangement - Google Patents

Description

TECHNICAL AREA

The invention relates to a radiation shielding device located at the outer surface of transport or storage containers for materials radioactive to ensure safety.

STATE OF THE ART

Containers for radioactive material generally include a envelope of great height comprising a cylindrical body and sealing means closing it at its two ends in a sealed manner; in the internal cavity thus delimited takes place of said radioactive materials, in particular irradiated fuel assemblies or vitrified waste.

This envelope must mechanically withstand impacts even the most severe, provide biological protection against radiation and ensure thermal transfer to dissipate the heat emitted by the materials radioactive.

Usually the cylindrical body essentially consists of a ferrule thick metal, for example based on cast or forged steel, cast iron, or a sandwich stacking of different metals; body thickness can reach several tens of centimeters and the container weight 100 to 150t.

The body often has fins on its outer surface to ensure better dispersion of heat in the atmosphere.

The fins can be fixed by bolting or welding, or be formed at the same time as the container when it is obtained by casting.

Thick metal body provides most of the protection biological, but is generally not sufficient to ensure the entire neutron protection.

Also to improve said neutron protection it is known to cover the body of a neutron absorbing material, for example solid resins light, which are generally cast between the fins while keeping them a sufficient size to ensure heat dissipation.

To avoid aging of these resins, it is also known to isolate them of the external atmosphere by confinement in enclosures or housings located on the body and fitted with cooling fins.

Application GB 2033287 describes the principle of the use of such boxes. hollow in good heat conducting material, filled with screen material neutron, with cooling fins and surrounding the body of the container. These boxes have a shape such that placed side by side they are overlap each other; they are mounted on removable belts surrounding the outer surface of the container and not directly on the container.

Application FR 2521764 describes a particular embodiment of the type of protection using housings filled with neutron shield material, which comes to be mentioned. The boxes are made up of very long profiles open longitudinally whose cross section is V-shaped at an angle obtuse summit. The profiles are arranged side by side, parallel to the axis of the container and in close thermal contact with the metal shell then welded to said ferrule and between them so as to form the so-called closed cases of large length. The housings are equipped with fins on their outer face.

After being placed on the shell, these boxes are then filled individually of neutron absorbing resin by casting by their open end.

Although these boxes fulfill their role of protection and containment of the material ensuring neutron shielding, their manufacture is particularly long and expensive. Indeed, it is necessary to carry out a great quantity of welds and filling of the boxes while these are already fixed on the shell of the container, which requires many and delicate handling a very heavy mass (up to 100 to 150 t, as has been already said) and causes a significant increase in the duration of realization.

Thus the Applicant has sought a shielding device by housings more simple to carry out to reduce the cost and also to improve the safety of the operations of making the boxes, of their fixing directly on the shell and their filling with radiation absorbing material, while improving contact and thermal evacuation. She also looked for a simpler and more simple method of fitting said shielding devices sure.

Furthermore in the case, more and more frequent, where the combustion rates fuel assemblies are increased, radioactive emissions from irradiated and waste assemblies are increased accordingly; the containers that intended for them then need enhanced biological protection. For absorb the additional neutron emissions it is possible to increase the thickness of absorbent material. On the other hand for gamma radiation, it it is not always possible to absorb it by an increase in thickness of the steel ferrule, which would either be at the expense of the ability of the container either at the expense of its weight and size the latter must remain suitable for transport on public roads.

it follows that it is preferable to add to the shell thicknesses of dense metal (for lead example) interposed between the shell and the neutron absorber.

Thus, the applicant has also sought a device which is simple to implement. work to increase the biological protection of containers.

Document DE-A-36 20 737 describes a container for transport and storage of waste radioactive. This container includes an outer container foundry iron containing graphite nodules and forming a screen against gamma and neutron radiation, as well as an inner steel container, received in a cavity defined in the outer container and container a basket suitable for receiving radioactive waste. A structure fulfilling a moderator function vis-à-vis the neutrons is received in an annular space formed between the two containers. This structure is formed of a number of polyethylene rings segmented and superimposed, between which are placed open elements for holding said rings, made of aluminum and having an H-shaped section

Finally, document FR-A-2 454 157 describes a container for transport and storage of assemblies of used nuclear fuel. The container includes a shielded container, around which a sheath of ribbed cooling formed from two to four elements assembled together. Each of these elements includes two concentric wall sections cylindrical metal, connected together by heat conductive sleepers, so as to define longitudinal cells closed at their ends and filled with neutron absorbing material.

DESCRIPTION OF THE INVENTION

The invention is a device for protection against radiation for transport container and / or radioactive material storage, the device comprising a plurality of metal housings adjacent, filled with at least one absorbent material neutrons, each case including an inner face conformed to the outer face of the container, one side exterior and parts connecting said faces interior and exterior, characterized in that each is an independent tubular profile, in one single piece closed longitudinally, in which said parts are side faces in contact with the lateral faces of the adjacent profiles, the device further comprising means for individually fixing each of the profiles on the outside of the container.

The container usually includes a ferrule thick cylindrical metal of great length on the outer face of which is fixed a plurality of closed or hollow tubular profiles in one piece according to the invention.

Said profile typically has a cross section closed polygonal, preferably with four sides corresponding to four longitudinal faces, and can be closed at its ends. Usually it is obtained by direct spinning and does not have a longitudinal weld or other means of closure. The absence of solder longitudinal or any other means of closure equivalent guarantees the housing a perfect seal not likely to deteriorate and keeps whatever happens all of its neutron shield properties.

It is usually made of metal, preferably good heat conductor like aluminum or its alloys, copper or its alloys ... It is fixed on said external face of the shell, parallel to its axis, typically by bolting, so that it has good thermal contact between said housing and said ferrule and between adjacent housings. All of the adjacent boxes generally cover the entire outer surface of the shell.

The outer face of the housing in contact with the ambient air is advantageously fitted with cooling fins spun with the profile or fixed on it by any other means.

Intimate contact via a large contact surface between the profile and the ferrule allows improved heat dissipation.

The profile is filled with neutron shield material, for example by pouring into it a resin with a high hydrogen content.

But the invention is especially advantageous when it is necessary to increase the protection against gamma radiation. It is then particularly simple to secure inside each profile constituting the housing, before their filling with resin and fixing them to the container, at least one plate metal, usually a heavy metal such as lead or its alloys, or a sandwich of plates of different metals chosen and assembled so as to simultaneously obtain optimal biological protection and good solidity of the assembly. This plate is located as close as possible to the container wall, i.e. typically in contact with the wall of the profile which is supported on the ferrule. Generally we use a lead plate covered by a protective steel plate to facilitate its fixing; this last is usually done using bolts going through the plates of steel, lead and the wall of the case in contact with the ferrule, screwed into said ferrule. Such a device makes it possible, in the event of an impact, to better retain the lead plate preventing it from coming to weigh directly on the walls of the case with the risk of deforming them.

The invention also relates to a method for installing a device radiation protection for transport container and / or storage of radioactive materials comprising a plurality of housings adjacent metal fixed to the outer wall of the container and container at least one neutron absorbing material characterized in that one introduces in the housing at least one biological screen material and then fixed said housing containing the biological screen material on the outer wall of said container.

The installation of the device according to the invention is therefore particularly simple. and can be done in two stages. First you just need to install optionally the lead plate and / or any other metal, then to sink said neutron shield material directly inside the profile; the profile thus prepared is then fixed on the shell of the container.

You can still, after having optionally installed the metal plates in the case, which represents the most delicate operation, fix the profile thus equipped on the shell and then pour the neutron shield material there.

It is also more conventionally possible, in the case where a metal plate not used, first fix the profile then fill it with screen material Neutron.

We see that in all cases no welding is necessary to close longitudinally the housing or fix it to the ferrule, which facilitates assembly and lower the cost. Handling necessary for the filling and filling the case can also be done by handling separately the profile not yet fixed on the shell; they are thus made easier and more safe.

The bolting operations of the case on the ferrule can be done by lights made in the face of the profile opposite to that which is in contact with the ferrule, lights which are then properly plugged in. When it is planned to pour the resin in the case before fixing it, it is advantageous to install passage tubes to the right of said lights in order to preserve a access into the cast resin for bolting; after fixing this space vacuum can be filled with resin.

We also see that the installation of lead plates in a device like that of the aforementioned patent FR 2521764 would be difficult to because the corresponding operations would have to be done while the container is already equipped with said boxes.

Figure 1 illustrates the device according to the invention. It represents a container for radioactive material seen in section and the detail of a view, always in section, of two adjacent housings according to the invention.

In (1) we see the thick metallic ferrule, usually made of steel, forming the body of the container in the cavity (2) of which the materials are stored radioactive. The container is handled using pins (3) fixed on the ferrule (1). A plurality of housings (4) according to the invention covers the wall outside of the ferrule (1).

Each of them essentially consists of a metal profile (5) hollow, closed longitudinally, with 4 long sides; of the cooling fins (6) are located on the outer face of said profiles. The inner face (7) is conformed to the outer face of the ferrule (1) of so as to ensure good thermal contact.

Inside each box a lead plate (8) has been installed in the contact of the inner face (7); this plate is covered with a sheet (9) protective steel. The assembly of the profile (5) and the plates (8, 9) is fixed to the ferrule (1) using bolts (11). The remaining interior space of the profile (5) is filled with a resin (10) making a neutron screen; in (12) we see a tube passage allowing bolting from the outer face of the profile (5) through the resin when it has been poured into said profile (5) before bolting.

Claims (10)

1. Device for protecting against radiation for a radioactive material transportation and/or storage container having a plurality of adjacent, metal chambers (4) filled with at least one neutron-absorbing material (10), each chamber (4) comprising an inner face (7) shaped onto the outer face of the container, an outer face and parts connecting said inner (7) and outer faces, characterized in that each of the chambers (4) is a longitudinally sealed, one-piece, independent, tubular section (5), in which said portions are lateral faces in contact with the lateral faces of adjacent sections (5), the device also incorporating means (11) for individually fixing each of the sections (5) to the outer face of the container.
2. Device according to claim 1, characterized in that each section (5) is of a metal chosen from the group comprising aluminium, copper and alloys thereof.
3. Device according to either of the claims 1 and 2, characterized in that each section (5) has cooling fins (6).
4. Device according to any one of the claims 1 to 3, characterized in that the fixing means are bolts (11).
5. Device according to any one of the claims 1 to 4, characterized in that each section (5) contains at least one metal plate (8, 9) forming a gamma radiation shield and located as close as possible to the container wall.
6. Device according to claim 5, characterized in that each gamma radiation shield-forming metal plate (8) is of heavy metal.
7. Device according to claim 6, characterized in that the heavy metal is chosen from within the group consisting of lead and its alloys.
8. Container for radioactive material transportation and/or storage comprising a device having a plurality of adjacent, metal chambers (4) filled with at least one neutron-absorbing material (10), each chamber (4) having an inner face (7) shaped to the outer face of the container, an outer face and parts connecting said inner (7) and outer faces, characterized in that it comprises a device according to the characterizing part of any one of the claims 1 to 7.
9. Process for putting into place a device according to any one of the claims 1 to 7 on the outer wall of a radioactive material transportation and/or Storage container, characterized in that it comprises at least one stage of introducing into each chamber at least one biological shield-forming material (8, 9), followed by a stage of fixing said biological shield material-filled chamber to the outer wall of said container.
10. Process according to claim 8, characterized in that into the chamber is introduced at least one metal plate (8) forming a gamma radiation shield and said chamber is then fixed to said wall and is filled with neutron-absorbing material.

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