The new designs are not going to be available for many years. They have to be proved in operation, particularly if they involve new chemistry like MSRs.
By the time they're proven, renewables will have expanded to global dominance and likely run down their experience curves to cost points that even Gen IV nuclear will find very hard to beat.
New nuclear designs are a hedge against renewables suddenly stopping getting cheaper. An insurance policy, but hopefully one that won't be needed.
Newer designs are fundamentally stable and fail in an inherently safe manner. Much, much less surrounding infrastructure and a greatly reduced need for system level fixes to problems since the catastrophic issues have been designed out.
It will take some time to turn the ship, but it is our best chance for producing 24 hour scalable power that is also carbon safe. Just search "modern nuclear reactor design" and start honestly reading the literature with an open mind.
A couple of random articles (plenty more available): https://www.technologyreview.com/s/512321/safer-nuclear-powe... http://science.time.com/2013/08/05/amidst-economic-and-safet...
Plenty of great information out there for anyone interested in letting go of their preconceived ideas and exploring the amazing work that is happening now.