[en] U-Mo dispersed fuel can not fulfill the U density requirements for high flux reactors. Besides, in-pile experiments have shown a large interaction between the fuel particles and the matrix. Replacing dispersed fuel by an U-Mo foil has been proposed and is currently under investigation as a possible solution to these problems. Friction stir welding is being experimented at ANL to fabricate fuel plates. Supported by the ENDE-CAC-CNEA experience in FSW, experiments have been started. Successful weld were obtained between aluminum and stainless steels (as subrogate material instead U-Mo) which allowed the selection of optimum parameters. This were applied to encase stainless steel and U-Mo foils in aluminum plates. The first objective was the implementation of the process, optimization of operative parameters and selection of the adequated tests to qualify the welding. The second objective was to apply these technic to fabricate U-Mo /Al alloys diffusion couples. First results are presented. (author)

[en] The monolithic U-Mo fuel elements consist in a foil of a U-Mo alloy encased in Al. One of the techniques that is being tried to apply in their fabrication is Friction Stir Welding in the 'no contact at the interface' mode. The Laboratory of Welding at the National Atomic Energy Commission (Argentina) has a great experience in the conventional form of this technique so has started working on this new application. This paper describes the experiments performed to obtain the operative parameters. In the first experiments AA6061 T6 (Al) plates and sheets of AISI 316 (SS) were used to obtain the optimal operative parameters of the process. Welds were performed and evaluated for different operative variables such speed, angle and diameter of the tool and tool-interface gap keeping the rotation speed constant. Tensile test, pressure leak-proof test, bending test, non-destructive test and metallography were used to characterize the welds. Finally, SS and U-Mo foils were encased using the parameters selected from the first experiments. The samples prepared with U-Mo alloy will be used as diffusion couples and for the studies of interdiffusion under irradiation. (author)

[en] The process of solid phase soldering by friction stir welding (FSW) was presented in 1991 by TWI (1) for aluminum alloys. The welding is generated by a tool that rolls over and moves on top of the joint. This process produces butt, torch and thread welding on flat surfaces. Unlike traditional fusion welding methods the joints do not need to be prepared, nor are gas protection or support material needed. No overlap or relevant distortions are generated and welds of up to 15 mm thick in a single pass are permitted. The initiation sites of fissures from butt welding, in a single pass, are characterized in this work, for the thermo-treatable 6.25 mm thick alloy AA 6061-T6. The tests were performed using a pulsing flexion testing machine. Using different techniques the initiation sites were found to be in the root zone, a few tenths of a millimeter below the surface. The results are analyzed considering the plastic flow pattern created by the tool and experimented by the material during the welding (cw)

[en] Full text: U-Mo dispersed fuel can not fulfil the U density requirements for high flux reactors. Besides, in pile experiments have shown a high degree of interaction between the fuel particles and the matrix generating large porosity. Replacing dispersed fuel by an U-Mo foil has been proposed and is being investigated as a possible solution to these problems. Friction stir welding (FSW) is being experimented at ANL to fabricate fuel plates. Supported by the ENDE-CAC-CNEA large experience in FSW, experiments have been started. Successful weldings have been obtained between Al and stainless steels as subrogate material instead U-Mo. The first objective is the implementation of the process, optimization of operative parameters and selection of the adequate tests to qualify the welding. The second objective is encase U-Mo foil in Al to be used as diffusion couples. (author)

[en] Out of reactor interdiffusion experiments between U-Mo alloys and Al alloys made close to fuel operation temperature are needed to validate the results obtained above 500 deg. C. A study of interdiffusion between U-Mo and Al or Al alloys, out and in reactor, has been initiated. The objective is to characterize the interdiffusion layer around 250 deg. C and study the influence of neutron irradiation. Irradiation experiments will be performed in the Argentine RA3 reactor and chemical diffusion couples will be fabricated by Friction Stir Welding (FSW) technique. In this work out-of-pile diffusion experiments performed at 340 deg. C are presented. Friction Stir Welding (FSW) was used to fabricate some of the samples. One of the results is the presence of Si, in the interaction layer, coming from the Al alloy. This is promising in the sense that the absence of Al rich phases may also be expected at low temperature. (author)