Uncertainty quantification of steady state depeltion solution using multi-physics coupling code system based on nodal diffusion code RAST-K

This study presents the uncertainty quantification results of steady-state depletion simulations using a multi-physics coupling framework based on the nodal diffusion code RAST-K. Developed for the analysis and optimization of pressurized water reactors, RAST-K integrates advanced methodologies and diverse engineering capabilities, consistently demonstrating strong agreement with measured data and commercial nuclear design codes. High-fidelity core simulations are conducted through the multi-physics coupling of RAST-K with the subchannel thermal-hydraulic code CTF and the fuel performance code FRAPCON. Notably, the consideration of dynamic gap conductance and thermal conductivity degradation in fuel performance calculations highlights discrepancies in pin-wise fuel temperature predictions. Uncertainty quantification is performed using stochastic sampling methods by perturbing both input parameters and nuclear data. The results indicate that uncertainties in global reactor design parameters, such as critical boron concentration, axial shape index, and peaking factor, are primarily driven by nuclear data perturbations, while thermal-hydraulic uncertainties are influenced by both input and nuclear data variations.