Decay heat calculations on LWR assembliesPutranto, Alfonsus Rahmadi (Avtor) Snoj, Luka (Mentor) Giot, Lydie (Komentor) Suikkanen, Heikki (Komentor) decay heatspent nuclear fuelMonte CarloLight water reactorsClabThis thesis extends the study of decay heat calculations in SUBATECH Laboratory focusing on the validation and verification in decay heat calculations in light water reactor assembly, presenting a decay heat calculation benchmark performed with the Serpent 2 Monte Carlo code and the ENDF/B-VII.1 nuclear data library, based on decay heat measurements re-evaluated at the Clab facility reported by EPRI and SKB. Automated framework to generate Serpent2 inputs from the EPRI report is developed, along with documentation of the differences identified in this re-evaluation of the SKB report. A key finding is that the EPRI nominal fuel density overpredicts decay heat by more than $4\sigma_E$, necessitating an assembly-specific effective density for accurate simulation. The statistics and modeling approaches are considered based on the calculation on F14 assembly of Ringhals 2. The reference modeling approach employs 5·10$^6$ neutrons with uniform pin-cell modeling and void as the gap-filling material, simulated using Doppler broadening rejection correction with reflective boundary condition. Decay heat calculation results on PWR assemblies are analyzed based on two metrics: the calculated-to-experimental ratio, $C/E$, and normalized bias, $(C-E)/\sigma_E$. These metrics are necessary but not sufficient for rigorous assessment, which requires propagating nuclear data and technological uncertainties. This falls outside the scope of the present thesis. First study of decay heat caculations on boiling water reactor assembly from Oskarshamn 3 is also performed. The results from this study have underprediction tendency compared to the measured decay heat, obtaining $C/E \pm 1\sigma$ of $0.9984 \pm 0.0079$ and $(C-E)/\sigma_E \pm 1\sigma$ of $-0.13 \pm 0.70$ for Ringhals 2 and $C/E \pm 1\sigma$ of $0.999 \pm 0.014$ and $(C-E)/\sigma_E \pm 1\sigma$ of $-0.22 \pm 0.99$ for Ringhals 3. Effects of void fraction on calculated decay heat in BWR assembly is also observed.20262026-09-18 08:15:07Magistrsko delo/naloga188069VisID: 164477COBISS_ID: 291640323sl