To better qualify the ability of nuclear power to contribute to the net-zero emissions transition, the nuclear power sector needs to understand its sensitivity to hydro-climatic and anthropogenic stresses at the local level. While current approaches based on statistical modelling can be used to assess climate change impacts on electricity networks at a global or national level, they are limited when extrapolated to regulatory thresholds at a local level.As part of a series of two papers aimed at assessing the impact of climate change on site-specific nuclear power outages, this paper presents a modelling chain for estimating hydro-climatic-policy scenarios for nuclear power generation. The second one will implement the modelling chain in context of climate change, based on downscaled IPCC scenarios, and applies the method to two contrasted French nuclear power plants.The modelling framework (power outages modelling bias of +7.0 %) appears as a strong basis for investigating the impact of climate change on nuclear power outages in terms of frequency and magnitude. Such work could inform on the evolving sensitivity of the nuclear fleet to support the energy grid, to potentially optimize its management, and to define water-energy nexus levers to better anticipate the effects of climate change.