In the short term, one would burn natural gas in turbines. The marginal cost of displacing this by using nuclear instead would lead to an enormous cost per unit of CO2 avoided, so high that most other uses of fossil fuels would be eliminated first (like, all use in ground vehicles).

In the long term, either non-fossil fuels burned in turbines (e-fuels like hydrogen or biofuels), or bulk thermal storage of renewable electricity. These both have lousy round trip efficiency (maybe 40%), but that's still cheaper than using batteries, because the capex per unit of storage capacity is far lower, and the cost of the RTE is low when there are so few charge-discharge cycles (as happens with seasonal storage); cost of seasonal storage is dominated by capex, which is why using high-capex batteries for it is such a bad idea.

Personally, I consider bulk thermal storage of cheap DC-coupled PV the most promising approach, as being pursued by Standard Thermal. They claim to be able to deliver 365/24/7 heat at 600 C for $3-5/GJ, which is competitive with Henry Hub natural gas.

> Then what would you use for seasonal storage?

Like Germany: coal and the energy provided by the rest of the EU. So Nordic countries hydro and nuclear, and some French nuclear.

While lobbying to make all those interconnections increase domestic prices for the providers.