The Department of Energy will make a major announcement Tuesday involving nuclear fusion, which has great potential as a sustainable, low-carbon energy source.

The department announced on Sunday that Energy Secretary Jennifer Granholm will make an announcement about a "major scientific breakthrough" made at Lawrence Livermore National Laboratory in California.

The Financial Times first reported the news on Sunday.

Nuclear fusion involves the release of a huge burst of energy.

"Nuclear Fusion reactions power the Sun and other stars," reads an explanation from the Energy Department. "In a fusion reaction, two light nuclei merge to form a single heavier nucleus. The process releases energy because the total mass of the resulting single nucleus is less than the mass of the two original nuclei. The leftover mass becomes energy."

The breakthrough comes from the National Ignition Facility, which used giant lasers to create conditions that briefly mimic the explosions of nuclear weapons. The scientists achieved a net energy gain for the first time in a fusion experiment using lasers, according to one of the sources.

It is considered a crucial discovery because controlling nuclear fusion energy was something not easily contained. It has been clear for years that the energy potential was there.

Nuclear fusion does not cause any environmental damage if contained properly.

Scientists hope one day it could provide a cheap source of clean electricity due to how much energy can be produced from a small process but the breakthrough does not mean the immediate availability of cheap fusion energy.

"Fusion has the potential to provide a near-limitless, safe, clean, source of carbon-free baseload energy," said Dr. Robbie Scott of the Science and Technology Facilities Council's Central Laser Facility Plasma Physics Group, and a contributor to the research. "This seminal result from the National Ignition Facility is the first laboratory demonstration of fusion 'energy-gain' – where more fusion energy is output than input by the laser beams. The scale of the breakthrough for laser fusion research cannot be overstated."