Nuclear power was supposed to save the planet. The plants that used this technology could produce enormous amounts of electricity without the pollution caused by burning coal, oil or natural gas, which would help slow the catastrophic changes humans have forced on the Earth’s climate. As a physicist who studied esoteric properties of subatomic particles, I admired the science and the technological innovation behind the industry. And by the time I started working on nuclear issues on Capitol Hill in 1999 as an aide to Democratic lawmakers, the risks from human-caused global warming seemed to outweigh the dangers of nuclear power, which hadn’t had an accident since Chernobyl, 13 years earlier.

By 2005, my views had begun to shift.

I’d spent almost four years working on nuclear policy and witnessed the influence of the industry on the political process. Now I was serving on the Nuclear Regulatory Commission, where I saw that nuclear power was more complicated than I knew; it was a powerful business as well as an impressive feat of science. In 2009, President Barack Obama named me the agency’s chairman.