Studsvik’s approach to spent nuclear fuel (SNF) analyses combines isotopic concentrations, fluxes, and cross sections, calculated by the CASMO5 neutron transport and depletion code, with irradiation history data from the SIMULATE5 reactor core simulator and tabulated isotopic decay data. These data sources are used and processed by the SNF code to compute the SNF characteristics. Recent advances in the system, including uncertainty analyses of the computed decay heat power, are presented in this paper. The decay heat power uncertainty is evaluated accounting for the uncertainties in the operating conditions and uncertainties in the nuclear and decay data. The model involves a series of stochastic perturbations combined with the linear propagation law. The uncertainty quantification complements the best estimate decay heat power.