The US Department of Energy is set to reveal a “major scientific breakthrough” this week after scientists were reportedly able to produce a fusion reaction that created a net energy gain for the first time. The development — a major milestone in the pursuit of limitless clean energy — was made recently at the government-funded Lawrence Livermore National Laboratory in California, sources told the Washington Post. The net gain reaction, which is considered to be a “holy grail” of zero-carbon power, is a major step towards being able to create a technology one day that could offer a clean and virtually limitless supply of energy. Energy Secretary Jennifer Granholm is expected to announce the results of the fusion experiment at a media event on Tuesday. A lab official said researchers were still finalizing their findings and nothing would be confirmed until the scheduled event.