This paper depicts the power system adequacy with respect to nuclear strategies by coupling investment with dispatching. The long-term energy model POLES simulates the Paris Agreement worldwide and is soft-linked with a power market model applied to France, EcoNUK. The nuclear flexibility is described by cycling frequency and amplitude, constrained by reactors minimum rated power and half-hour ramping rates. Results in 2050 show that the French power system made of 26% nuclear and 71% renewables in POLES needs deeper and longer flexibility with nuclear and gas in EcoNUK, due mainly to higher granular time-steps than the prospective model; and that reactors perform more deep cycles than allowed by their license (230 instead of 200). We show that scenarios with high shares of renewables build on the arbitrage between nuclear and gas, notably during peak loads in winter and night periods. Meeting the double target to reduce nuclear and carbon emissions requires more renewables, hence significant gas and nuclear power for adequacy, facing the dilemma nuclear versus emissions. Coupling short-term operation with long-term investment indicates that nuclear flexibility varies with the time-step of intermittency modeling, so scenarios need to include reactors constraints to reach an informed decision on renewables and nuclear.