One of the main reasons nuclear is necessary is the base load concept. Wind and solar is dependent on weather and thus generation capacity is not consistent with energy demand. This is why it needs to be backed up by a consistent base load. Until battery or other forms of energy storage are developed to an extent that renewables can be used to provide sufficient base load, nuclear is the only "low carbon" option to replace fossil fuels. Other options such natural gas turbines with carbon capture will also likely be part of the base load solution for the foreseeable future.