We need a system where a) renewables generate the energy, b) batteries help smooth the system and where c) gas turbines or engines provide capacity rather than generate much energy.
Getting rid of the last 5 per cent of non-fossil electricity generation is the most difficult. But doing it through nuclear power is unachievable. We would need something like green hydrogen, produced from renewable energy, and kept in storage.
There are other possible solutions, and no doubt they will develop as technology progresses. But of course, apart from putting together demonstration schemes, we do not need to do this in the next few years. What we do need to do now is, as well as rapidly expanding renewable energy, is to expand electrification into the low hanging fruit of decarbonisation. That means, as first stops, electrifying heat and transport. Building more nuclear power plant merely wastes the meagre funds that are being currently spent on decarbonisation.