In 1979, one of two nuclear reactors at the Three Mile Island power plant near Harrisburg, Pennsylvania, suffered a partial meltdown. The second reactor was shut down 40 years later for economic reasons. Now, work is underway to restart that second reactor to produce electricity for a single customer, Microsoft. To learn what it takes to restart and ensure the safety of a nuclear power plant, and to explore the role of nuclear energy in a mix of renewable resources, we’ve invited back Dr. Elmer Lewis, professor emeritus of mechanical engineering at Northwestern University. Dr. Lewis is the author of the books “Nuclear Power Reactor Safety” and “Fundamentals of Nuclear Reactor Physics,” and he will soon publish his latest book, “Renewables or Nuclear, Which Should Lead in Curbing Climate Change?