Patent Number: 
Section: description

The container as illustrated in FIG. 1 has the general form of a rectangular box. The container 1 is defined by four vertically arranged walls 2 and a base wall 3. The walls are provided at the corner joins with strengthening elements 4 in the form of L-shaped strips. The vertical strengthening elements 4 have portions 6 which extend beyond the lid 8 of the container. Feet 10 are provided on each corner of the base and engage with the portion 6 for easy and stable stacking. The outer skin forming the walls 2, base 3 and separate lid 8 are made of stainless steel. A peripheral flange 12 is provided around the container. The lid 8 is dimensioned to be slidably received within the boundaries of the L-shaped elements 4. The lid 8 has a flange 16 which corresponds with the peripheral flange 12 of the container. Handles 14 on the lid aid in its removal and insertion. In the closed and retained position shown the lid 8 is retained by a series of quick release nuts and bolts 18 which engage corresponding openings in the flange 16 of the lid 8. The lid is provided with suitable seals to prevent any ingress of water. Next to the steel skin the container is provided with a substantial thickness of a thermal insulator 20 formed from calcium silicate. This layer is provided in a series of sections, see FIG. 2. The materials provision in solid sections ensures accurate positioning during assembly and use. A single base layer of insulator 22 and four wall sections 24 line the container itself. When the container is loaded, as described below, a two piece insulating top layer is applied. These two pieces 26, 28 are shaped to interconnect with one another. The rectangular box defined by the interior surfaces of the insulating layers receives an internal container 30A having four walls and a base and also made of boronated steel or stainless steel. This container 30A is also provided with a lid 31 as shown in FIG. 1. As seen in FIG. 3 the container consists of a series of interlocking vertical walls 30 made of boronated steel/stainless steel. The container 30A has two pairs of internal walls 30 at 90 degrees to one another defining nine chambers 32 within the pail load. In use within each of the eight peripheral chambers a fuel drum or pail 36 is received. The central chamber 32A is provided with a polyethylene neutron absorber 38. The absorber 38 is itself provided in a steel container (not shown) which corresponds with the shape of the chamber 32 into which it is to be fitted. A lid is provided on the top of the absorber to retain the absorber in place in the chamber 32A. Once the internal container 30A has received all eight fuel drums 36, and the container 1 is sealed by applying the lid 31, the insulating top layer 26, 28, and the external lid 8. The lid 8 is secured to the container 1 by the quick release nuts and bolts 18. The fuel containing drum 36, as illustrated in FIG. 6, consists of a stainless steel cylinder wall 40 with a base plate 42 and releasable lid 44. The lid 44 is provided with a standard internal lever clamp band 46 which enables the lid to be secured to the fuel drum 36. The provision of the internal lever clamp band 46 within the outline of the drum 36 is important to minimize the space taken up. In the closed state the drum 36 is water tight avoiding any water ingress. The fuel 55 in either powder of pellet form is contained within polyethylene bags. The polyethylene bags filled with fuel are placed in a larger polyethylene bag which is placed in the drum. Once the larger bag is full this is then closed. The drum is then sealed with the lid 44. The fuel may typically be enriched uranium destined to form fuel rods. In the second embodiment of the invention illustrated in FIG. 7 the container 100 is once again in the form of a rectangular box. The external container 100 is defined in a similar manner to the container of the first embodiment by vertically arranged side walls 102 and a base wall 103. Other equivalent elements are numbered with reference numerals corresponding to those used in the first embodiment increased by 100. Thus the strengthening elements, feet, peripheral flange, lid fixing and lid alignment are provided in a similar manner. The container 100 is also provided with substantial thickness of thermal insulator 120 provided by a base section, wall sections and a section optionally mounted on the lid in a similar manner to the first embodiment of the invention. The arrangement within the internal cavity defined by these insulating layers differs, however. The cavity is provided with a series of stainless steel sleeves 150 which are rigidly mounted on a bottom plate standing on the base layer insulation. The cylindrical sleeves are hollow and have an internal dimension configured to snugly correspond to the external dimensions of the fuel containers 152 shown inserted in the sleeves 150. Nine sleeves 150 are used in a three by three arrangement with a fuel container 152 being positioned in each in use. The fuel containers are generally of the type illustrated in FIGS. 6 and 6A above, but include external fasteners projecting beyond the plan of the fuel containers. As shown in FIGS. 7, 8 and 9 the sleeves 150 are surrounded by a neutron absorbing material 158. This material is introduced to the volume surrounding the sleeves during the manufacture of the portion of the assembly filling the internal cavity by pouring in a liquid resin which is then allowed to harden. A resin tight unit is preferred as defining this cavity. The resin is loaded with boron preferably to a level of 2% to provide the desired neutron absorbing capability. A boron loading up to 6.5 wt % and/or a lead loading up to 15 wt % may be provided. The material offers between 1xc3x971022 and 1xc3x971023 hydrogen atoms/cm3  To reduce the cost and weight of the neutron absorbing material, typically 1.68 g/cm3 lighter materials such as polystyrene can be incorporated in portions where the neutron absorbing volume of material would otherwise be excessive. Thus at locations 162 between sets of 4 sleeves and externally at the corner locations 164 and locations 166 between the pairs of sleeves the neutron material may be replaced with the lighter material. This does not affect the neutron absorbing capability of the container. The fuel containing drums 152 and the manner in which the fuel, as powder or pellets is provided within them is as described above for the first embodiment of the invention. The present invention allows approximately 20%-40% of the outer container volume to be occupies by fuel 55 and yet still meets the necessary standards. This compares favorably with prior art systems. An increased payload is thus provided successfully. The use of stainless steel and the modular nature of the assembly assists in refurbishment and any cleaning stages required such as decontamination.