Patent Publication Number: US-8534481-B2

Title: Tank containment assembly for transporting uranium hexafluoride

Description:
This application is a 371 of PCT/EP2009/063083 filed Oct. 8, 2009. 
     The invention relates to an assembly particularly for transporting UF 6 , comprising an inner container with skirting panels extending from said container and projecting beyond the end surfaces thereof, and an outer container which holds the inner container and is comprised of a first and a second shell, wherein when the shells enclose the inner container, they preferably lie one on top of the other in a plane in which or parallel to which the longitudinal axis of the inner container extends, and wherein a valve extends outward from one of the end surfaces of the inner container, which valve is enclosed by the outer container and is spaced therefrom, and is covered externally by at least one impact-absorbing element. 
     Uranium hexafluoride (UF 6 ) is transported in cylindrical steel containers. These containers are specified in ISO 7195 “Packaging of Uranium Hexafluoride (UF 6 ) for Transport” and in ANSI N14.1 “Uranium Hexafluoride—Packaging for Transport.” During transport, these containers must meet IAEA requirements specified in TS-R-1 “Regulations for the Safe Transport of Radioactive Material,” and the requirements of international and national regulations derived therefrom. Steel containers for uranium hexafluoride enriched to more than 1 wt % uranium-235 in uranium are enclosed for transport in an outer container which acts as a protective container, and which must comply with the aforementioned regulations. 
     Containers that contain uranium hexafluoride enriched to more than 1 wt % but no more than 5 wt % uranium-235 in uranium must comply with the following requirement, among others, which result from the normal and accident transport conditions defined in TS-R-1: 
     The steel container, or inner container, the protective container, or outer container, and the contents consisting of uranium hexafluoride make up the shipping article as described in the regulations. 
     In addition to tests 1 to 4 described in what follows, there can be no physical contact between the valve extending outward from the inner container and any other component of the packaging, with the exception of its original point of connection, and additionally, the valve must remain tightly sealed following test 5, described in what follows.
     1. A free-fall test from a height, which is based on the weight of the shipping article (1.2 m for a shipping article weight of 5,000 kg, 0.3 m for a shipping article weight of more than 15,000 kg, with additional stages between these two threshold values), onto an unyielding surface.   2. A puncture test using a steel rod weighing 3.2 kg, dropped onto the shipping article from a height of 1 m with the tip pointing toward the shipping article.   3. A drop from a height of 9 m onto an unyielding surface.   4. A drop from a height of 1 m onto a steel cylinder having a diameter of 150 mm and a minimum length of 200 mm.   5. A heat test, in which the shipping article is exposed to fire at a temperature of 800° C. for a period of 30 min.   

     The required protective function can be provided by an outer container, also referred to as protective packaging, which completely encloses the steel container filled with uranium hexafluoride, in other words the inner container, wherein the outer container, i.e., the first and second shells, each of which forms a half shell, has a cladding made of sheet steel, for example, which encases impact absorbing and thermally insulating material, for example, foam. 
     There are currently two basic types of protective containers in use for the purpose of protecting the valve. 
     In a first embodiment, a form-fitting positioning of the valve to be protected is dispensed with. Therefore, because the valve is arranged at the end surface, reinforcement over large areas of the end surfaces of the protective container is necessary, because an improper loading or rotation of the container during transport cannot be reliably ruled out. If reinforcement is implemented in only localized areas, there is a risk that the valve may be positioned outside of the reinforced area and therefore inadequately protected. In this embodiment, both end surfaces must be reinforced, because the valve side of the steel container is not assigned to a specific end surface of the protective container. With inadequate reinforcement of the end surfaces, there is a risk that physical contact between the valve and some other component of the packaging may occur, since the distance between valve and interior wall of the protective container is only a few millimeters. 
     In a second embodiment, the steel container is positioned over a bored hole in the skirting panel welded to the steel container, by means of a bracket attached on the side in the protective container. In the region of the valve, the protective container has an interior recess and exterior reinforcement. 
     In both embodiments, the steel container, or the inner container, is supported in the protective container, or the outer container, exclusively via the skirting panel. Calculations performed using the finite elements method show that in the first embodiment, a jack-knifing of the skirting panel, with the associated damage to the valve, cannot be ruled out. In the second embodiment, the areas adjoining the skirting panel are reinforced and support said skirting panel, however, weight and costs are significantly higher with the second embodiment than with the first. 
     DE-T-699 02 774 relates to an encasement for holding a cylinder in which uranium hexafluoride is held. At its end surfaces areas, the cylinder has skirting panels. 
     Moreover, a valve extending in the longitudinal direction of the cylinder projects outward from one end surface and is encompassed by one of the skirting panels. 
     The subject matter of DE-A-28 54 358 is a container for transporting radioactive materials, which can be sealed with a cover through which a drainage channel extends. The channel transitions to a valve, which is enclosed by a hood-like cover seal. 
     A container for transporting uranium hexafluoride has valves at its end surfaces, which valves are enclosed by hood-like caps that project inside skirting panels, which extend in a lengthening of the circumferential walls of the container (WO-A-2004/072985). 
     A transport assembly according to EP-A-0 777 238 comprises an inner and an outer container. The inner container has continuous skirting panels at its end surface areas. Projecting from one end surface is a valve, which is positioned inside one of the skirting panels and extends to the container, spaced therefrom. 
     According to U.S. Pat. No. 5,777,343, a container for holding uranium hexafluoride has continuous skirting panels at its end surface areas for the purpose of protecting valves that extend outward from the end surfaces. 
     The problem addressed by the present invention is that of configuring an assembly of the type specified at the beginning in such a way that a specified positioning of the valve extending outward from the inner container, and therefore a positioning of the inner container in relation to the outer container that encloses it, in other words, the protective container, is ensured. A further problem is that of ensuring adequate protection of the valve against the stresses specified in the aforementioned regulations. Moreover, as compared with the known embodiments, a reduction in cost with a simultaneous reduction in weight is to be achieved, without changes to the dimensions. 
     According to the invention, the problem is solved essentially in that the impact-absorbing protective element projects, movable, for example pivotable and/or shiftable, from one of the shells as the first shell of the outer container or from the skirting panel of the inner container extending on the valve side, in that when the inner container is positioned correctly in relation to the outer container, the protective element covers the valve, and in that the protective element is covered externally by at least one of the shells when the outer container is closed. 
     In particular, the invention provides that the movable, for example pivotable, element or protective element has or consists of a first section, which is remote from the valve and is on the side of the joint, and a second section, which covers the valve. In this case, the first section can be supportable on the end surface that extends on the valve side. Alternatively or additionally, the second section can be supported on the skirting panel that encompasses the end surface like a ring. It is also possible for at least one support element which is supported on the valve-side end surface to extend outward from the second section. 
     On the basis of the teaching according to the invention, the movable, for example pivotable and/or shiftable, impact-absorbing element—also called a device—ensures that the inner container must be aligned correctly in relation to the first shell of the outer container, from which the pivotable element projects in principle, in order for the element to pivot in such a way that the valve is covered to the necessary extent. Without the correct positioning, the impact-absorbing element cannot be moved, for example pivoted, such that the second shell can be placed on and connected to the first shell to enclose the container. 
     Accordingly, a defined positioning of the valve and therefore of the inner container in relation to the protective or outer container which encloses the first container is ensured, wherein at the same time, adequate protection of the valve against the stresses specified in the aforementioned regulations is provided. Requirements with regard to dimensions and weights are met, and the cost of the protective container is reduced. 
     According to the invention, the protective container, or the outer container, is equipped with a movable, for example hinged, protective device (element), which is filled with impact-absorbing materials and is reinforced in the region of the valve; said element positions and/or encloses the valve in said device by means of an optional positive connection and decreases stresses on the skirting panel by means of large-area support of the steel container, such that a jack-knifing, and therefore damage to the valve, can be ruled out. 
     According to the invention, the protective device can be connected to the first shell, i.e., the lower part of the protective container, via a hinge, so that, once the lower part has been loaded with the steel container filled with uranium hexafluoride or some other material, particularly radioactive material, the protective device can be moved, for example folded down, into the required, correct position. The upper part can be placed onto this only when the valve is positioned correctly in the device. The device is fixed in place by the upper part of the protective container. 
     According to the invention, the movable protective element prevents the valve from being loaded into the protective container opposite the element, because in this position, the element cannot be moved as necessary, for example folded down, and the upper part of the protective container cannot be placed onto it. 
     The protective container, which contains the element according to the invention as an integral component, can be loaded only with the provided orientation of the steel container and positioning of the valve. 
     The impact-absorption provided in the movable element relieves stress on the skirting panel, which could jack-knife as a result of the stresses, since the protective element either projects beyond the skirting panel or extends on the outside at least within a plane which is spanned by the outer edge of the skirting panel. This capability is not offered by any embodiment currently in use. 
     The use of lightly impact-absorbing materials in the movable element results in a substantial decrease in the weight of the protective container as compared with the embodiment currently in use. 
     The use of localized reinforcements, which can be applied effectively through the positioning of the valve, increases security while simultaneously decreasing weight. 
     In particular, it is provided that the impact-absorbing element, in other words the protective device, is pivotable about an axis which extends parallel or approximately parallel to the plane in which the shells lie one on top of the other. The longitudinal axis of the inner container preferably extends within this plane. 
     It is further provided that the shell that covers the impact-absorbing element, in other words the second or upper shell, is not as thick at its end surface as the first or lower shell. 
     A further development of the invention also provides that the first section of the pivotably embodied element has a particularly stepped section on the joint side, into which the first shell engages positively when the outer container is closed. 
     Independently thereof, the protective element should have a cladding made of steel, such as stainless steel, which can have a wall thickness ranging from 10 mm to 20 mm. The cladding then holds impact-absorbing material, which is at least one material from the group comprising phenolic resin, polyurethane foam, and wood, for example balsa wood. 
     According to the invention, the impact-absorbing element, also called the device, is arranged so as to be movable in relation to the inner container. Movable in this case includes a pivoting and/or shifting. The pivotable and shiftable protective element can be embodied such that it consists of a first section, which is preferably pivotable about 90°, and a second section connected to the first, for example hinged thereto, which can be displaced in relation to the first section. Displacement can be carried out before, after or during the pivoting of the first section. 
     It is also within the scope of the invention for the element to consist of multiple sections connected via joints or hinges. 
     Additional details, advantages and features of the invention are specified not only in the claims, the features found therein—alone and/or in combination—but also in the following description of an embodiment example depicted in the drawing. 
    
    
     
       The sole FIGURE shows a longitudinal section of an assembly  10  particularly for transporting uranium hexafluoride, which is also called shipping packaging. The assembly  10  comprises a steel container for holding the uranium hexafluoride, for example, as an inner container  12 , and an outer container  14 , which acts as a protective container, and which is in turn composed of two half shells  16  and  18 . The lower shell  16  is referred to as the first shell and the upper shell  18  is referred to as the second shell. When the outer container  14  is closed, the shells  16 ,  18  preferably lie on top of one another in a plane which extends in or parallel to the longitudinal axis of the inner container  12 . 
     
    
    
     The inner container  12  can be made of boiler steel and has skirting panels  20 ,  22  welded to it, which project beyond the respective end surfaces  24 ,  26  of the inner container and extend in the direction of the circumferential walls of the inner container  12 . 
     For filling the inner container  12 , a valve  28  projects outward from the left end surface  24  in the drawing. Said valve  28  must be protected in such a way that it will withstand the above-described tests. 
     According to the invention, it is provided that the valve  28  is covered by an element  30  as valve protection, which has impact-absorbing properties. 
     In the following description of the embodiment example, the impact-absorbing element  30 , which can also be called the protective element, is embodied as pivotable. However, the teaching according to the invention is not restricted to this. Rather, the element  30  is movable in some way, allowing it to be aligned to the valve  28  as necessary for protecting said valve. Said alignment is also required for the shells  16 ,  18  of the outer container  14  to be assembled correctly. 
     In the embodiment example, the protective element  30  projects outward from the lower or first shell  16  and is pivotable about an axle  32  which extends parallel to the plane in which the shells  16 ,  18  of the outer container  14  lie one on top of the other. 
     The protective element  30  consists of a first section  34 , which is hinged to the lower shell  16 , and, when the inner container  12  is aligned correctly in relation to the lower shell  16 , and therefore when the shells  16 ,  18  are assembled, thus forming the closed outer container  14 , is supported on the end surface  24 . The first section  34  transitions to a second section  36 , which extends above the valve  28  and is supported, for example, against the skirting panel  20  or, via support elements  44  extending from the section  36 , against the end surface  24 . 
     The first section  34  further has a stepped notch  35 , in which, when the inner container  12  is positioned correctly—and therefore the protective element  30  rests against the end surface  24 , which is made possible only by this correct position—an inner edge of the lower shell  16  rests. The axle  32 , made particularly of stainless steel, extends spaced from this edge, so that, as a result, the end wall  37  of the upper shell  18  is not as thick in the region of the protective element  30  as outside of this element, as is clear from the drawing. 
     It is also clear from the sole FIGURE that the protective element  30  extends over the skirting panel  20 , in other words projects over said skirting panel, when the protective element  30  is positioned correctly and encloses the valve  28 , preferably spaced from it. 
     The first section  34  can be about 200 mm thick, for example, and can extend lengthwise along the end surface  24  by approximately 300 mm, without this serving to restrict the teaching of the invention. 
     Only when the inner container  12  is aligned correctly in relation to the lower shell  16  and therefore to the protective element  30  can the protective element  30  be pivoted toward the container  12 , in order to place the upper shell or second shell  18  onto the container  12  and connect it to the lower shell  16 . Therefore, the protective element  30  performs a dual function. For one, the protective element  30  serves as protection for the valve  28 . For another, the protective element  30  ensures that the inner container  12  must be aligned correctly in relation to the lower shell  16  in order to seal the outer container  14 , and thereby complete the shipping article. 
     The lower and upper shells  16 ,  18  each have cladding  38 ,  40  comprised particularly of stainless steel, in which impact-absorbing material is inserted, which must also provide thermal protection. The density of the material in the cladding  38 ,  40  can vary, with greater density in the region of the end surfaces than in the region of the side walls. For instance, in the region of the side walls, essentially thermal protection must be ensured, whereas the end regions must be able to withstand the above-described tests. 
     The material inserted into the cladding  38 ,  40  or stainless steel shell can be polyurethane foam, phenolic resin or balsa wood, for example. 
     The pivotable or hinged protective element  30  has a cladding  42  comprised of stainless steel. Inside the cladding  42 , an impact-absorbing material such as phenolic resin, polyurethane foam or balsa wood is inserted. In the section  34  that extends on the side of the joint, the cladding can have a wall thickness of 2 mm to 4 mm, for example, and in the front section  36 , it can have a wall thickness of 10 mm to 15 mm, for example. 
     The different shading in the lower and upper shells  16 ,  18  is intended to symbolize different densities. The area between the skirting panels  20 ,  22  and end surfaces  24 ,  26  of the inner container  12  and the facing inner end surfaces of the shells  16 ,  18  is not filled with material—apart from the protective element  30 .