** Shares of U.S. nuclear sector companies rise premarket after President Donald Trump's speech in Davos
** "We are very much into the world of nuclear energy," says Trump
** Cos engaged in developing small nuclear reactors: NuScale Power SMR.N up 6.4%; Nano Nuclear Energy NNE.O gains 5.6%; Sam Altman-backed Oklo OKLO.N up 7.8%
** Uranium producers: Centrus Energy LEU.N, enCore Energy EU.O and Uranium Energy UEC.A gain between 2.9% and 4.5%
** Nuclear utilities: Vistra Corp VST.N gains 2%; GE Vernova GEV.N up 1.8%; Constellation Energy CEG.O rises 2.3%
(Reporting by Sumit Saha in Bengaluru)
((Sumit.Saha@thomsonreuters.com;))