U.S. to announce scientific breakthrough on fusion energy -sources

WASHINGTON, Dec 12 (Reuters) - The U.S. Department of Energy will announce on Tuesday that scientists at a national lab have made a breakthrough on fusion energy, the process that powers the sun and stars that one day could provide a cheap source of electricity, two sources with knowledge of the matter said.

The scientists at Lawrence Livermore National Laboratory in California have achieved a net energy gain for the first time, in a fusion experiment using lasers, one of the people said. The FT first reported the experiment.

Fusion works when nuclei of two atoms are subjected to extreme heat of 100 million degrees Celsius (180 million Fahrenheit) or higher leading them to fuse into a new larger atom, giving off enormous amounts of energy.

But the process consumes vast amounts of energy and the trick has been to make the process self sustaining and to get more energy out than goes in and to do so continuously instead of brief moments.

If fusion is commercialized, which backers say could happen in a decade or more, it would have additional benefits including the generation of virtually carbon free electricity which could help in the fight against climate change without the amounts of radioactive nuclear waste that today's fission reactors produce.

Running an electric power plant off fusion presents tough hurdles however, such as how to contain the heat economically and to keep lasers firing consistently. Other methods of fusion use magnets instead of lasers.

Energy Secretary Jennifer Granholm is slated to hold a media briefing on Tuesday at 10:00 a.m. EST (1500 GMT) on a "major scientific breakthrough."

The department has no information ahead of the briefing, a spokesperson said.