Steel is one of the most CO2 intensive material produced in Europe. Its production represents 4% of France GHG emissions. To meet EU decarbonization targets and quit coal, steel producers can rely on several decarbonization options: incremental upgrading of existing assets with biomass or carbon capture, investments in new assets that use natural gas or hydrogen, or a shift towards recycled steel. Many challenges appear from this potential transition as producers would face technology and prices uncertainty. They would have to develop first-of-a-kind plants and be exposed to unknown energy markets. Furthermore, investments needs are diverse and while some solutions need a high upfront cost, other investments can be spread over some decades. To capture those dynamics, we use a compound real options framework with MonteCarlo simulations to model the future of the French primary production of steel. Commodity & technological risks are modelled with stochastics variables. We consider possible transitions between decarbonization technologies to accurately model those long living assets. We show that carbon price volatility with a fixed 2050 target, has a strong impact on investment decision and might greatly increase the cumulative emissions by delaying investments in net-zero compatible assets. This framework allows to assess the impact of CfD - Carbon for Difference- schemes, where the governments would derisk investments by guaranteeing a carbon or commodity price over the investment's life. Insights are provided on possible trade-offs between decarbonization policies such as CfD, operative costs subsidies, or technological development subsidies.