By Sarah McFarlane, Timothy Gardner and Susanna Twidale WASHINGTON/LONDON (Reuters) – U.S. firms developing a new generation of small nuclear power plants to help cut carbon emissions have a big problem: only one company sells the fuel they need, and it’s Russian. That’s why the U.S. government is urgently looking to use some of its stockpile of weapons-grade uranium to help fuel the new advanced reactors and kick-start an industry it sees as crucial for countries to meet global net-zero emissions goals. “Production of HALEU is a critical mission and all efforts to increase its production are …