That report is a reasonable snapshot of knowledge at the time, but it was published in 2014 and some of the underlying data dates back to 2000. You can see the data sources that went into the technology-specific metrics in Annex II:

https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5...

"The data on nuclear power was taken from Lenzen (2008) and Warner and Heath (2012)."

"Photovoltaic power: Ranges are based largely on the reviews of Hsu et al. (2012) and Kim et al. (2012)."

"Wind power: The data is based on the review of Arvesen and Hert-wich (2012) and has been cross-checked with Dolan and Heath (2012) and Hertwich et al. (2013)"

Let's go back to the Hsu review cited for photovoltaic generation.

"Life Cycle Greenhouse Gas Emissions of Crystalline Silicon Photovoltaic Electricity Generation: Systematic Review and Harmonization"

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1530-9290....

If you look at tables 1 and 2, it's aggregating studies from the years 2000-2009. Most are from 2006 or earlier. Solar manufacturing has improved a lot and costs have fallen dramatically since 2006. At the same time, nuclear projects under development since 2006 in Europe or the USA have cost much more than originally planned.

China continues to build new reactors; it's an existence proof that new reactors can be built. But China also builds wind and solar farms cheaper than Europe or the USA. You can't get a Chinese energy project at Chinese domestic prices in either the USA or Europe.