[en] Aluminium-base dispersions of U₃ O₈ 20% enriched were chosen for the reactor fuel. The preparation of the U₃ O₈ consist on the precipitation of a solution of U O₂ F₂ with NH₄ OH followed by calcining and sizing operations. The U O₂ F₂ solution is obtained by hydrolysis of U F₆. Since 1986 the PFPU produced powders for fuel fabrication. This paper study the influence of process parameters in the yield of the U₃ O₈ fabrication. The quality and the progress in the different productions were analyzed. (author)

[en] CNEA, the Atomic Energy Commission of Argentina, has defined development and fabrication activities related with the main fields of the RERTR program. This includes the qualification of high-density fuels for research reactors, the production of radioisotopes from LEU targets and the reduction of the HEU inventory. This paper continues previous presentations in past RERTR meetings and summarizes the main activities performed in these fields during 2002- 2003 and future works. The main part of the CNEA U₃Si₂ Qualification Program will be completed within this year. The irradiation of the first fuel element was finished and the activities are mainly focused on its PIE works. Regarding the UMo field, development works to provide support for fuel plate fabrication process and to improve understanding of UMo-Al interaction are on progress. Depending on the results of the fuel plate fabrication setup, the manufacturing of full size FE for UMo qualification program could take place during 2004. A program related with the UMo monolithic fuel is also in progress. In the radioisotopes field LEU targets have replaced HEU-Al alloy targets for routine Mo-99 production since November 2002. CNEA approach to minimize the Argentine HEU inventory is also presented (author)

[en] At present, obtention of U₃O₈ used in the manufacturing of MTR plates nuclear fuels, is performed by hydrolysis of UF6 to obtain uranyl fluoride. Uranyl fluoride is precipitated with ammonium hydroxide to get ammonium polyuranate (ADU). Afterwards ADU is calcinated to U₃O₈ and mechanical and thermally treated in order to obtain a powder in a determined specification. In the present work, ultrasound has been applied in the stage of precipitation of ADU and for different times in the stage of digestion in order to fasten the stages of ADU filtering and eliminate the U₃O₈ milling and sieving. Experiences on UO₂ have also been performed. The aspect of ADU changes considerably when they have been ultrasonically treated, its filtering rate is faster and it is easier to dry as it contains less humidity. U₃O₈ obtained after 800degreeC calcination of treated ADU results in an easy to desagregate powder. Only a soft mechanical treatment is needed to be performed on it before starting thermal treatment at 1400degreeC. After thermal treatment at 1400degreeC treated U₃O₈ has shown adequate characteristics of size, shape and density (8.2 g/cm³). Regarding UO₂, the shape of the agglomerates is almost spherical, leading to a free-flowing powder, whose apparent and TAP density showed to be adequate. The characteristics of the different compounds were followed by electron scanning micrographies, X-Rays, specific area measurements and differential thermal analysis. The great advantage of ultrasound appliance is that hard mechanical treatment is avoided in the obtention of U₃O₈, saving time and effort. Furthermore, UO₂ proves to be adequate to make pellets, the same precursor could be used in the obtention of both uranium oxides. (author). 5 refs., 6 figs

[en] Ammonium Diuranate (ADU) is the nominal name for ammonium poliuranate. It is a very complex compound whose polymeric structure may have different chemical composition and crystallographic structure according to the precipitation conditions. ADU is used as precursor of uranium oxides in the manufacture of fuel elements. In order to find the composition of ADU its thermal decomposition was studied. Thermogravimetric analysis were performed and samples were taken in the singular points. These samples were analyzed by X-ray diffraction and infrared spectroscopy. Electron scanning photographs were taken. Besides an experience was designed in order to identify the evolved products during heating. When ultrasound has been applied in the precipitation stage, the ADU has the composition 6 U O₃.3 N H₃. 9 H₂ O. The ADU precipitated without ultrasonic treatment has the formula 6 U O₃. 4 N H₃. 8 H₂ O. The difference between both ADU is the adsorbed water or lightly coordinated water, which is present in more quantity in the ADU without ultrasonic treatment. (author)

[en] The conversion of high flux reactors to LEU requires the development of monolithic high density fuels. The radiation performance of uranium-molybdenum (UMo) high density fuel has shown excellent behaviour of fission gas products retention and reasonable swelling. The development of monolithic UMo is usually approached from the point of view of an aluminium cladding. Interface interactions between these two materials could be an issue and fabrication procedures have to be radically changed because of the big difference in mechanical properties of core and clad. An alternative way of looking at these scenario is using zircalloy-4 (Zry-4) cladding for the U-Mo monolithic fuel. The basic idea was to study the possibility of colamination of both materials to fabricate plates. A series of preliminary studies where performed to look at the feasibility of this alternative. Calculations where done to analyze stress generation because of the different coefficient of thermal expansion of both materials. Diffusion couples where studied for evaluation of the interface growth. Zry-4 plates where colaminated for selecting ranges of colamination temperatures and deformation steps. Several miniplates where elaborated with depleted uranium and 20% enriched uranium (LEU) for irradiation purposes in the RERTR experiments in the Advanced Testing Reactor (ATR, INL). All miniplates where elaborated looking at scale production of full size plates for irradiation purposes and fuel fabrication. The fabrication steps are the casting of the alloy, machining to core dimensions, cutting of frame and lids, welding (TIG) of boundaries, hot colamination, straightening of plates, abrasive finishing of plate surfaces and cutting to final dimensions. Characterization results will also be shown: metallography, ultrasonic scanning (scan-C), radiography, etc. The elaboration of U-Mo monolithic plates with Zry-4 cladding, as achieved, is a possible flexible technological alternative for fuel fabrication and conversion purposes that does not involve big changes in the usual equipment of production plants of plate fuels. (author)

[en] CNEA, the National Atomic Energy Commission of Argentina, is at the present a qualified supplier of uranium oxide fuel for research reactors. A new objective in this field is to develop and qualify the manufacturing of LEU high-density fuel for this type of reactors. According with the international trend Silicide fuel and U-xMo fuel are included in our program as the most suitable options. The facilities to complete the qualification of high-density MTR fuels, like the manufacturing plant installations, the reactor, the pool side fuel examination station and the hot cells are fully operational and equipped to perform all the activities required within the program. The programs for both type of fuels include similar activities: development and set up of the fuel material manufacturing technology, set up of fuel plate manufacturing, fabrication and irradiation of miniplates, fabrication and irradiation of full scale fuel elements, post-irradiation examination and feedback for manufacturing improvements. For silicide fuels most of these steps have already been completed. For U-xMo fuel the activities also include the development of alternative ways to obtain U-xMo powder, feasibility studies for large-scale manufacturing and the economical assessment. Set up of U-xMo fuel plate manufacturing is also well advanced and the fabrication of the first full scale prototype is foreseen during this year. (author)

[en] Full text: During 2004, CNEA performed several RERTR activities, including: LEU Very High Density Fuel development: two national technical meetings has taken place. During 2004 works are being focused on: - U-Mo powder development and fabrication, - research on U-Mo based ternary systems, - Mo-Al diffusion couples out-of-pile experiments, - 3-D thermal mechanical modelling of fuel behaviour under irradiation, - atomistic modelling and experimental fuel particle and sheet coating, - development of new matrix, new fuel particle and sheet, and new cladding, - development of advanced welding techniques to be applied on monolithic fuels. LEU high density fuel fabrication activities: - status of fabrication tasks of silicide fuels for RRR reactor. LEU radioisotope production targets: two years of success - target fabrication, irradiation and radioisotope production. Argentinean spent fuels: plans and projects - intermediate storing - final conditioning. (author)

[en] During 2004 several activities related to RERTR topics has taken place. In what follows, a resume of those activities is presented. During 2004 the Nuclear Fuel Cycle Program has supported the activities of about a hundred of researchers and technicians involved on different aspects of Very high density fuel developpement (VHD) fuel development as R and D, mini-plates, plates and fuel assemblies fabrication, irradiation and PIE analyses of VHD fuels. CNEA's LEU MTR fuel waste disposal plans are concerned with spent fuel from the reactor RA-3. The SF will be kept in interim storage until a geological repository is available for disposal. According to the current planning, this repository would be available in the year 2050 to receive the SF from the NPPs or the HLW from their reprocessing. Since 2002 the domestic production of Mo99 and other fission radioisotopes is performed using LEU targets, fulfilling international technical and quality standards. Up to present more than 600 targets bearing LEU material have been fabricated irradiated and processed. Very recently CNEA has also become an international supplier of targets for Mo-99 production. This status report deals as well with the International framework i.e. Global Threat Reduction Initiative and the historical involvement of Argentina in the peaceful applications of nuclear energy

[en] One of the main objectives of CNEA regarding the fuel for research reactors is the development and qualification of the manufacturing of LEU high-density fuels. The qualification programs for both types of fuels, Silicide fuel and U- x Mo fuel, are similar. They include the following activities: development and set up of the fissile compound manufacturing technology, set up of fuel plate manufacturing, fabrication and irradiation of mini plates and plates, design and fabrication of fuel assembly prototypes for irradiation, post-irradiation examination and feedback for manufacturing improvements. This paper describes the different activities performed within each program during the last year and the main advances and achievements of the programs within this period. The main achievements may be summarized in the following activities: Continuation of the irradiation of the first silicide fuel element in the R A3. Completion of the manufacturing of the second silicide fuel element, licensing and beginning of its irradiation in the R A3. Development of the HMD Process to manufacture U-Mo powder (pUMA project). Set up of fuel plates manufacturing at industrial level using U-Mo powder. Preliminary studies and the design for the irradiation of mini plates, plates and full scale fuel elements with U-Mo and 7 g U/cm³. PIE destructive studies for the P-04 silicide fuel prototype (accurate burnup determination through chemical analysis, metallography and SEM of samples from the irradiated fuel plates). Improvement and development of new characterization techniques for high density fuel plates quality control including US testing and densitometric analysis of X-ray examinations. The results obtained in this period are encouraging and also allow to foresee a wider participation of CNEA in the international effort to qualify U-Mo as a new material for the manufacturing of research reactor fuels. (author)

[en] The Atomic Energy Commission of Argentina has been involved in the Reduced Enrichment for Research and Test Reactors Program since 1978. The most relevant milestones of the program, regarding fuel R and D activities, were the development and manufacturing at industrial scale of U₃O₈ dispersed fuel assemblies and the conversion of the RA-3 reactor core to LEU fuel. More recently, the activities were focused in the development of high density U₃Si₂ fuel with a density of 4.8 gU/cm³ and the improvement of the manufacturing process of U₃Si₂ powder. Currently one of the main objectives is to develop and qualify the technology for the production of high-density LEU fuel elements using U-Mo alloy. Several alternative ways to obtain U-Mo powder are under development with the aim of evaluating plant scale production and costs. To boost this program the main research reactor of Argentina, the RA-3, will be upgraded to 10 MW early in 2001 and the hot cells at the Ezeiza Atomic Center are fully operational after important investments. Significant progresses were also carried out in the development of LEU targets for the production of Mo⁹⁹. Experimental work has demonstrated the feasibility of the manufacturing and radiochemical processing of miniplate targets prepared with dispersed UAl_x, maintaining the geometry and the alkaline processing of the HEU targets used so far. (author)