Not everyone is happy to have nuclear energy in the mix at all. Personally, I'm not a great fan of nuclear fission (the existing nuclear technology) myself - I'm prepared to go along with it if it proves necessary/wise - a 'fill-in' position in the long-term picture. But I am in favour of nuclear fusion technology, which is much cleaner (much less radiation, and radiation half-lives of decades rather than centuries) and fundamentally safer - it's so difficult to maintain the fusion reaction over time that the 'default' setting if something breaks is for the reaction to stop immediately.
The issue we have, unfortunately, is that nuclear fusion is still decades away from commercial reality at scale, and so any new nuclear plants coming on stream over the next twenty years or so (say to 2050) are highly likely to be fission reactors rather than fusion reactors.
Controversy arises, therefore, over whether new fission reactor nuclear power plants are 'necessary', and how strong that necessity is depends on who you speak to. There is an argument that nuclear is not necessary at all, and sufficient low carbon energy can be obtained using other technologies. There are so many factors that impact on the argument that there can be numerous, equally valid, viewpoints on the desirable energy mix of the future. Here are just some of the factors:
- Cost (of generation) per unit of energy
- Cost of transmission/distribution
- Fuel availability and security of sources of supply
- Total energy demand estimates
- Whether an efficient and fair market exists for energy
- Mixture of public and private financing
- Size of capital investments and length of time of investments
- Risk appetite of private sector investors
- Waste storage (eg radioactive waste)
- Safety during operation
- Cost of energy to end-consumers - and to what extent it includes infrastructure investment costs
- Intermittency of energy generation and availability of cost-effective energy storage
- Monopoly or near-monopoly power among market participants
- Extent of distributed energy generation (reducing the need for expansion of the national grid)
- 'Capacity Margin' considerations