[en] The IAEA Vienna organized a Coordinated Research Project (CRP) on improvement the computer codes used for fuel behaviour simulation under the name: FUMEX III.The major research objective of this CRP would be to test and develop fuel modeling codes against experimental data and cases provided by IAEA and OECD/NEA. Institute for Nuclear Research (INR) Pitesti participated at this CRP with ROFEM and CAREB computer codes.The main aim of ROFEM code was to calculate fuel behaviour during steady state operating conditions.CAREB code was developed for fuel transients analyses such as LOCA and RIA.Recently both codes have been improved with new models in order to extend their capabilities. - The individual models included in the ROFEM and CAREB codes have been reviewed in order to improve these models and the predictive capabilities of the codes. - In order to analyse the CANDU fuel behavior in transient/accident conditions,the code ROFEM has been coupled with CAREB code. - The FUMEX 3 CANDU reactor specific cases have been simulated with ROFEM,and CAREB codes. Satisfactory agreement was found for both steady-state and transient conditions .The calculations results reflects trends and changes of fuel design parameters and linear power history. - Further work for improving and refining the models of the present codes is necessary but it is strongly dependent of the available experimental data base - New in reactor instrumented tests aiming to cover the fuel modeling problems are already in progress in TRIGA SS reactor and TRIGA Power Pulse reactor of INR Pitesti. (author)