Patent Number: 041525850
Section: summary

BACKGROUND OF THE INVENTION The present invention concerns an assembly for the transport and storage of radioactive fuel elements. For the conveyance of fuel elements it is known to use sealably closed transportation flasks. During conveyance irradiated fuel elements are submerged in liquid (for example water) within the flask to dissipate heat generated by the decay of fission products and thereby limit the fuel temperature. While provision must be made for change of volume of the liquid in the flask, it is important that irradiated fuel elements are submerged at all times during conveyance. In British Pat. Specification No. 1378681 there is described and claimed a sealably closable fuel element transportation canister for containing fuel elements submerged in liquid having self-regulating ullage means arranged so that within a chamber for containing the fuel elements the free space can be maintained full of liquid. In particular there is described a canister having a primary chamber for containing the fuel elements submerged in liquid, a secondary chamber for containing liquid and pressurised gas and a duct interconnecting the chambers and arranged for forming an air lock there between whereby the free space in the primary chamber can be maintained full of liquid. It is now considered that it is not necessary for the chamber containing the fuel elements to be full of liquid although there must be sufficient liquid in the chamber for the fuel elements always to be submerged in the liquid. This condition is important for transportation flasks in which the fuel elements are loaded into the flask in one orientation and the flask is transported in a second orientation. SUMMARY OF THE INVENTION Accordingly the present invention provides an assembly for the transport and storage of radioactive fuel elements, comprising a transport flask and a fuel element holder disposed in the flask so that fuel elements in the holder may be submerged in liquid within the flask and the assembly may be used in one orientation for loading the fuel elements and in another orientation for transporting the fuel elements, the assembly having self-regulating ullage means comprising reservoirs for containing liquid and a pressurised gas and the arrangement of the reservoirs being such that in either orientation of the assembly liquid is maintained in all the reservoirs to prevent egress of the pressurised gas therein and to compensate for volume changes arising from temperature variations within the flask. In a preferred arrangement elongate reservoirs are provided around the fuel element holder. The reservoirs may each have two communications between the interior and exterior of the reservior, the first of the communications being at the end of the reservior which is lowermost when the assembly is in a vertical position used for loading and being so placed that it is below the level of the liquid in the reservoir when the assembly is in a horizontal position used for transport, the second communication comprising a tube extending from said lowermost end of the reservoir to a point of opening which is above the level of liquid in the reservoir in the vertical position of the assembly used for loading but below the level of liquid in the reservoir or reservoirs in the horizontal position of the assembly used for transport, the tube being shaped to prevent egress of the pressurised gas when the assembly is in the horizontal position. The assembly may include a basket assembly on which the reservoirs are located. The basket assembly receives the fuel elements which may be enclosed within fuel canisters.