

Another solution would be adding some intelligence to water heaters. Have a temperature control valve on the output where you set the temperature, and program the water heater get to 160-180°F when electricity is cheap. This would be a thermal battery that would easily level out demand for electricity for heating water.
This has been done for close to a century in wind or run of river hydro heavy countries (as well as some coal ones).
The water heater has a buffer tank and is attached to a meter that only runs when a signal is sent across the power line. This stores about 20kWh for a 300L tank.
Modern insulation would allow going up to a few m^3 for a couple weeks’ worth.
Even if you could magically increase the number of nuclear reactors started before 2012 tenfold to keep up with wind and solar, you’d have to triple uranium mining overnight to fuel them for the first time.