Development of an incremental methodology for tracking the burnup-dependent isotopic vectors of fuel elements in the TRIGLAV program package for research reactorsTorres Garcia, Jesus Israel (Avtor) Trkov, Andrej (Mentor) Research reactorfuel element burnupTRIGLAVisotopic vectorsAn incremental methodology has been developed to consider the isotopic changes of the fuel elements during their burnup process in the TRIGLAV code. Through the modification of the internal subroutines and the implementation of new and auxiliary programs, the incremental scheme tracks the exact isotopic concentrations of the pin-cells (fuel elements) as they undergo the depletion cycle by saving the specific material compositions of the unit-cells at every intermediate burnup step in master isotopic libraries. These updated libraries, carrying the isotopic vectors of the fuel as a function of burnup, serve as input data in the subsequent cross-section homogenization before undergoing the global diffusion calculation. The resulting burnup and isotopic distributions from this new methodology were compared with the data from the original -integral- scheme and from Serpent simulations through their relative differences. In every case the root-mean-squared deviations are less than 1%, so the model remains validated. Highest discrepancies arise from the TRIGLAV's treatment of the unit-cells that represent partially inserted Control Rods. The analysis showed that the resulting burnup levels for the individual pin-cells are mismatching because in the incremental scheme the cross-section homogenization is following more closely the number density changes of the unit-cells at each intermediate step of the depletion cycle, hence impacting their specific burnup increments (dBU). It has also been noted that the individual isotope densities for particular pin-cells have increasing differences when compared (up to 5%) depending on their position inside the core, and thus on their burnup process. Overall, the study explored the physical effects of the isotopic changes in a research reactor and the significance of tracking the burnup-dependent isotopic concentrations of the fuel elements.20252025-05-29 08:15:06Magistrsko delo/naloga169454sl