This article presents two economic analyses performed with the Marino model, which was specially designed to analyse the costs of different spent nuclear fuel (SNF) management strategies in the real Spanish context. These analyses are: (a) a Monte Carlo study for those strategies and (b) the effects of a longer operational lifetime for the Spanish nuclear power plants (NPPs) on the costs of spent nuclear fuel (SNF) management. For the first analysis, a triangular distribution for the different unitary costs was assumed and the data and assumptions from numerous studies were used to obtain the values required for the distribution. The second analysis was performed for the current official shutdown dates for the NPPs, and the results were compared to other operational lifetime scenarios. The main assumption for these scenarios was a progressive shutdown of the reactors, in order to avoid numerous shutdowns in a few years. These scenarios were proposed for 40 to 60 years of mean operational lifetime of the reactors. The results show that, for all scenarios analysed, the additional electricity production due to longer operational lifetimes compensate the extra costs caused by the larger amount of SNF to be managed. Additionally, for the current SNF management strategy, a progressive shutdown at 40 years of mean operational lifetime has shown to entail lower costs than the official shutdown scenario. However, a strategy without a centralised interim storage facility would be the most economically favourable one for all the scenarios analysed.