According to the IPCC the median life-cycle CO2 emissions of nuclear energy are roughly the same as for onshore and offshore wind, and about a quarter those of utility scale solar PV. With the exception of hydropower in exceptional circumstances, and biomass, renewables and nuclear have low carbon intensity.
Claims that nuclear energy does not have a low carbon footprint, such as a 2015 article “False solution: Nuclear power is not ‘low carbon’” in The Ecologist, rely on a non-peer-reviewed study by Storm van Leewen and Philip Smith (sometimes referred to as the "Stormsmith" study). In a rebuttal of the "StormSmith" work, researchers from the Paul Scherrer Institute found that Storm van Leeuwen's estimate of the energy consumed by Uranium mining and milling in Namibia was higher than the energy consumption of the entire country.
An article on “The Energy Reality Project” blog discusses the StormSmith study. (Note that some of the links on the blog page no longer work.)