I'm not an expert on nuclear power, but I did like the comparison this Greenpeace video made that

Nuclear power is like smoking cigarettes to keep the weight off...

Why not use renewable energies instead? They're there for the taking!

The perspective in the video is a bit smoke and mirrors. It shows electricity ('power') as a 20-ish percentage of the energy mix, and nuclear as a portion of this.  It's important to realise that this is based on final energy use, i.e. delivered energy to consumers.

If we make the same graph based on primary energy, or greenhouse gas emissions, electricity would represent a larger part of the slice, around 35-40% of total.

If we look at the future energy mix, the demand for heat could be to a very large extent eliminated. Today, passive houses mean a 90% reduction of demand for space heating. 

So if we were to draw a picture based on primary energy consumption, in a future system where demand for heat is reduced dramatically, the pie chart will look very different, and electricity will be a major part of it.

In addition, the use of electricity in transport is expected to increase as well, through plug-in hybrids, electric vehicles and public transport.  

Can we do without nuclear? It would be good to see a plan for future electricity supply without nuclear in which the numbers add up.

Is nuclear power sustainable? Probably not today, but with future development on passive safety, advanced waste treatment and fast-neutron reactors and eventually fusion, it holds tremendous promise. The debate should not be 'nuclear or not', but 'nuclear under what conditions' and 'at what cost'.

A future society that truely masters the power of the atom will look very differently from a renewables-based society. But success is far from certain.