Construction of the Kalpakkam fast reactor in India. (International Atomic Energy Agency)
The New York Times had a forward-looking piece on the development of advanced nuclear reactors that gives an interesting overview of the status of technology in the United States, citing ongoing research at places like Argonne National Laboratory as the groundwork for eventual development of advanced reactors:
… if the world decides in the 2030s and 2040s that it is time to deploy a new fleet of reactors, those will be based on work done in the few labs like this over the next decade, experts predict.
That leaves out one salient point: Russia and India have built large advanced fast reactors. Full story