[en] Full text: A collaboration agreement between ANL/USDOE and CNEA Argentina in the area of Low Enriched Uranium Advanced Fuels has been in place since October 16, 1997 under the 'Implementation Arrangement for Technical Exchange and Cooperation in the Area of Peaceful Uses of Nuclear Energy'. An annex concerning DART code optimization has been operative since February 8, 1999. Previously, as a part of this annex a visual thermal FASTDART version and also a DART TM thermomechanical version were presented during RERTR 2002 and RERTR 2003 Meetings. During this past year the following activities were completed: - Optimization of DART THERMAL code Al diffusion parameters by testing predictions against reliable data from RERTR experiments. - Improvements on the 3-D thermo-mechanical version of the code for modeling the irradiation behavior of LEU U-Mo monolithic fuel Concerning the first point, by means of an optimization of parameters of the Al diffusion through the interaction product theoretical expression, a reasonable agreement between DART temperature calculation with reliable RERTR PIE data was reached. The 3-D thermomechanical code complex is based upon a finite element thermal-elastic code named TERMELAS, and irradiation behavior provided by the DART code. An adequate and progressive process of coupling calculations of both codes at each time step was reached. The coupling of the various components of the calculation was benchmarked and validated against RERTR PIE data. Various results will be shown during RERTR2004 meeting. (author)