[en] Adding a small number of highly reactive (fresh) fuel elements to a spent reactor core is an economical way to extend the core life-time. The performance of the reactor and the utilization of the fuel strongly depend on the location of the fresh fuel elements within the matrix of the less reactive (spent) fuel. The determination of the optimal loading pattern requires extensive calculational and experimental analysis. Such calculational analysis (supported by the experiments) was performed for the TRIGA reactor at the 'Jozef Stefan' Institute in order to determine the optimal loading pattern for the core, consisting of two types of fuel elements (FLIP and SS-clad). In this paper, a brief description of the calculational method will be presented together with the results. The comparison with the experimental results will be treated. General conclusions concerning utilisation of fuel in multi-zone TRIGA reactor will be drawn with special respect to core life-time improvement. (orig.)