Mark Jacobson (senior fellow Stanford University Precourt Institute for Energy and author of “The Solutions Project“, 100% renewable energy by 2050) claimed nuclear is being replaced by wind and solar, OnPoint podcast of December 3, 2015 (start listening at the 40:30 mark). He is likely referring to nameplate capacity, but not actual energy produced. When reviewing the USA’s Energy Information Administration stats and comparing electricity production for the entire years of 2014 and 2015, it is clear that when coal and nuclear are shut down, their production is replaced almost entirely by natural gas, which Josh Freed stated in that same podcast (39 minute mark).
This piece points out that wind and solar grew 20,659 MWh from the entire year of 2014 to the entire year of 2015. It does not mention that natural gas grew by 208,459 MWh during that same time period (although one can see that when viewing the graphics within the article).
Feel free to add to the conversation on twitter @tder2012