Induced nuclear reactions: processes – systems – and elements – Handling of fission reactor component structure within... – Storage container systems for new and/or irradiated core...
Reexamination Certificate
1999-02-26
2001-02-27
Jordan, Charles T. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Handling of fission reactor component structure within...
Storage container systems for new and/or irradiated core...
C250S506100
Reexamination Certificate
active
06195404
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an anti-radiation shielding device that is installed on the outer surface of containers used to ship or store radioactive materials in order to ensure safety.
DESCRIPTION OF THE RELATED ART
Containers for radioactive materials generally comprise an elongated envelope that comprises a cylindrical body and leaktight sealing means used to close the container at both ends. The internal cavity contained within said envelope houses said radioactive materials, particularly irradiated fuel assemblies or vitrified waste.
The envelope must be capable of withstanding even the most violent mechanical impact, provide biological protection against radiation and ensure thermal transfer in order to release heat created by the radioactive materials.
Usually the cylindrical body is mainly constituted by a thick metal ring that is manufactured, for example, using cast or forged steel, cast iron or layers of various metals. The thickness of the body can be as much as several tens of centimeters (i.e. 20, 30 cm etc.) and the container can weigh between 100 and 150 tonnes.
The body often comprises fins on the outer surface that are used to disperse the heat more effectively into the atmosphere.
The fins can be fastened using bolts or welding or they can be shaped at the same time as the container is cast.
The thick metal body provides most of the biological protection but is generally insufficient to ensure complete neutron protection.
Therefore, in order to improve said neutron protection techniques are known where the body is covered with a neutron absorbing material, for example light solid resins, that are generally poured between the fins such that said fins remain a sufficient size suitable for thermal release.
In order to avoid the resins aging, techniques are also known whereby the resins are isolated from the external atmosphere by being contained within chambers or housings located on the body and equipped with cooling fins.
British patent application 2033287, for instance, describes the use of hollow chambers of this kind that are manufactured in a suitable heat conducting material, said chambers being filled with a material that forms a neutron shield and equipped with cooling fins surrounding the body. The chambers are shaped in such a way that they lie side by side and overlap each other. Said chambers are mounted on removable belts that surround the outer surface of the container and are not fitted directly onto the chamber.
French patent application 2521764 describes a particular embodiment of the type of protection that uses chambers filled with a material constituting a neutron shield, as mentioned above. The chambers are composed of elongated sections that are open along their length and have a V-shaped cross section that forms an obtuse angle. The sections are fitted side by side parallel to the axis of the container and in close thermal contact with the metal barrel. Said sections are then welded to said barrel and to each other such that they constitute said elongated closed chambers. The outer surface of the chambers are fitted with fins.
Once the chambers are positioned on the barrel they are individually filled with a neutron absorbing resin that is poured through the open end.
Although the chambers adequately protect and contain material that is used as a neutron shield, they require particularly long and expensive production methods. The chambers require a large amount of welding and filling once said chambers are already fastened onto the barrel of the container. Many difficult operations involving maneuvering an extremely heavy weight (between 100 and 150 tonnes, as mentioned above) are therefore needed. These operations cause a significant increase in the duration of manufacture.
The applicant has therefore invented a shielding apparatus using chambers that are more simply produced in order to reduce the cost and also to improve safety during operations to manufacture the chambers, to fasten them directly onto the barrel and fill them with a radiation absorbing material, and also to improve contact and thermal release. The applicant has also invented a simpler and safer method for positioning said shielding apparatuses.
Moreover, in examples that are more and more common, where the burnup rates of combustible assemblies have increased, the radioactive emissions of irradiated assemblies and waste are increased to the same extent. The containers intended for their use therefore require reinforced biological protection. In order to absorb the additional neutron emissions it is possible to increase the thickness of the absorbing material. It is not always possible, however, to absorb gamma rays by increasing the thickness of the steel barrel as this would lead to a reduction in the capacity of the container and an increase in weight or volume. These increases must be taken into consideration as the containers must remain suitable for transport on the public highway.
It may therefore be understood that dense metal (lead for example) is preferred which is inserted in layers between the barrel and the neutron absorber.
Therefore, the applicant has also invented an apparatus that is simple to implement and that enables the biological protection of the containers to be increased.
SUMMARY OF THE INVENTION
The invention relates to an anti-radiation device that is intended for containers used to transport and/or store radioactive material, said apparatus comprising a plurality of adjacent metal chambers that are fastened onto the outer surface of the container and that are filled with at least one neutron absorbing material, characterized by the fact that each chamber mainly comprises a tubular metal section built as a single part that is essentially closed along its length.
The container of to the invention generally comprises a long, thick, cylindrical metal barrel on the outer surface of which are fastened a plurality of tubular sections that are open or closed and built in a single piece.
Said section typically comprises a straight, closed polygonal cross-section, preferably with 4 sides that correspond to 4 longitudinal surfaces, and may be closed at the ends. Said section is usually produced using forward extrusion and does not include longitudinal welding or other closing means. The absence of longitudinal welding or other equivalent closing means results in the chamber being completely leaktight and not subject to deterioration with time. It is indispensable that the resin will not deteriorate and that it will preserve all its qualities as a neutron shield under any circumstances.
Said section is generally metal, preferably of a good heat conductor such as aluminum or aluminum alloys, copper or copper alloys etc. It is fastened onto said outer surface of the barrel parallel to the axis, usually using bolts, such that good thermal contact is created between said chamber and said barrel and between the adjacent chambers. The assembly of adjacent chambers generally covers all the outer surface of the barrel.
The outer surface of the chamber that is in contact with the outside air is advantageously provided with cooling fins that are extruded in a single piece with the section or fastened onto said section using any other means.
The close contact provided by a large contact surface between the section and the barrel improves the heat release.
The section is filled with a neutron shielding material that is achieved, for example, by pouring a hydrogen-rich resin into the section.
However, the invention is mainly advantageous when it is necessary to increase protection against gamma rays. It is then extremely simple to insert at least one metal plate inside each section constituting the chamber before said chamber is filled with resin and fastened to the container. Said metal plate is usually of a heavy metal such as lead or lead alloys or layers of various selected metals that are assembled such that they achieve both optimal biological protection and suitable assembly rigidity. Each plate is located as near as possible to
Francois Dominique
Lemogne Andre
Dennison, Scheiner Schultz & Wakeman
Jordan Charles T.
Mun Kyongtaek K.
Societe pour les Transports de l'Industrie Nucleaire - Tran
LandOfFree
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