GB1055818A - Transit flask for radioactive objects - Google Patents

Abstract

1,055,818. Shielded containers for radio-active material. COMMISSARIAT A L'ENERGIE ATOMIQUE. Dec. 7, 1964 [Dec. 6, 1963], No. 49708/64. Heading B4Q. An air-tight and shielded flask for protection and transportation of radio-active objects, more particularly irradiated fuel elements, comprises and outer metal easing 2 surrounding a shielding material 1 and provided on its inside surface with at least one pocket 20 bounded by a deformable metal sheet 19 welded to the casing and filled with a fusible alloy which liquefies at a predetermined temperature, means being provided to permit the alloy to escape from the casing 2 to form an expansion volume for the shielding material 1 should a sufficient increase in the temperature inside the flask occur. In the embodiment illustrated, a cavity 3 bounded by a cylindrical jacket 4 at the centre of the flask contains a rotatable drum 5 having six chambers 6 for receiving containers 7 in which fuel elements 8 or other radio-active objects are disposed. The latter are introduced through a rotatable closure drum 9. The drum 5 is rotatable by means of a crank 14 while the drum 9 is rotatable by means of a control rod 13. A handling bar 15, a closure plug 16 and various gaskets 17 and fixing screws 18 complete the flask. A suitable alloy for filling the pockets 20 is a lead-antimony alloy containing 8% by wt. of antimony while a suitable shielding material 1 is a lead-antimony alloy containing 4% by wt. of antimony. The pockets 20 in this embodiment communicate with the outside of the casing 2 through apertures 21 which are normally closed by air-tight plugs 22 of lead-bismuth alloy and preferably also stoppers 23 of plastics material. In the event of an intense fire inside the flask, for example as a result of the violent combustion of a fuel element 8 in the drum 5, the temperature rise in the flask is such as to cause rapid melting of the lead-antimony alloy in the pockets 20. At the same time, the lead-antimony alloy of the shielding material 1 becomes malleable and exerts a thrust on the sheets 19, causing the molten alloy contained in the pockets 20 to be emptied therefrom through the apertures 21 after destruction of the plugs 22 and stoppers 23 as a result of the considerable temperature rise. The stresses on the metal casing 2 are thus rendered negligible and the internal cavity 3 is not deformed.