Alternative Fabrication Method of U Polycrystalline Foils for Mo-99 Irradiation Target

K.-H. Kim, M.-K. Son, S.-J. Oh, D.-B. Lee, B.-C. Lee (Sp), C.-K. Kim, Korea Atomic Energy Research Institute, Daejeon (Korea, Republic) 
As the uranium foils for Mo-99 irradiation target, which are charged into a reactor, can be conventionally fabricated at laboratory scale, but not yet at a commercialized scale by a hot rolling method due to some problems in foil quality, productivity and economic efficiency, an attention has shifted to the development of new improved technology. Under these circumstances, an alternative fabrication method of U polycrystalline foils has been investigated using a cooling roll casting method, in order to produce a fission isotope Mo-99, the parent nuclide of Tc-99m. Mo-99 irradiation targets, which are used in producing medical diagnosis, Tc-99m, are fabricated through the wrapping of Ni foil, the extension and the welding of Al tubes, using the uranium foils obtained by a cooling-roll casting method. Continuous polycrystalline uranium foils with a thickness range of 100 to 150§­ and a width of about 50 mm are fabricated with the high quality of uranium foils and the high economic efficiency of the foil, through the variations of the various process parameters. The dimension and the surface state of the uranium foils are adjusted with the revolution speed of cooling roll, the ejection pressure of melt, the gap distance between nozzle slot and cooling roll, the superheat of the metal, and the atmosphere of melting and casting. The uranium foils fine polycrystalline grains below about 30 microns in size with the ¥á-U phase, irrespective of process parameters. It is expected that fine grain microstructure prevents the uranium foils from excessive swelling by an-isotropic growth behavior during irradiation.

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