An energy start-up backed by Microsoft Corp. co-founder Bill Gates is in discussions with Toshiba Corp. on developing a small-scale nuclear reactor that would represent a long-term bet to make nuclear power safer and cheaper.<p>Toshiba said it is in preliminary discussions with TerraPower, a unit of Intellectual Ventures, a patent-holding concern partially funded by Mr. Gates. Intellectual Ventures, based in Bellevue, Wash., is run by a former Microsoft Corp. executive, Nathan Myhrvold.