The general 3X20 European directive proposes renewable penetration goals. In France, 27% of the electricity is to be produced by renewable resources by 2020 and this share will be continuously growing up to 2050. Among these resources, some-like wind and solar-are not dispatchable, which triggers challenges to maintain the reliability target level of the power system, both in the short and long term. Wind and solar are expected to contribute to about 12% of the French electricity production in 2020 and according to voluntaristic scenarios they could contribute to over 50% of the total electricity production by 2050. The increase of the non-dispatchable renewable share in the power system modifies the residual demand (which is equal to the demand minus non-dispatchable renewable production) pattern to more power ramping and higher variation amplitudes. To keep the system balanced, backup options are numerous, though scarcely considered exhaustively in power systems modelling. Besides peaking unit production-such as gas turbines-which is usually the preferred option, storage, demand (or supply) curtailment, interconnections and baseload (nuclear for instance) power modulation should also be considered, particularly in such a context of high non-dispatchable renewable penetration. In a French context of significant production of nuclear power, nuclear modulation is investigated as a feasible opportunity to facilitate renewable energy penetration. Available capacity is assessed based on realistic scenarios and through the use of residual load duration curves. The load modulation impact on the nuclear levelized cost of electricity is estimated, and nuclear backup option is compared to gas on economic and environmental terms. Gas backup is more competitive than nuclear in each of the studied scenarios, but including a carbon-tax could change the trends (as low as €20/tonCO2 in some cases). This advocates for such incentives to avoid the effective greenhouse gas release. Nuclear backup would be all the more competitive than power plants used are amortized.