North Korea now has the capability to manufacture a nuclear warhead that can be placed on a rocket, a significant step forward in Kim Jong Un's efforts to develop nuclear missiles, a top U.S. commander told reporters on Friday.

Lockheed Martin Corp said Wednesday that it had made a technological breakthrough in developing a power source based on nuclear fusion, and the first reactors, small enough to fit on the back of a truck, could be ready for use in a decade. Tom McGuire, who heads the project, said a small team had been working on fusion energy at Lockheed's secretive Skunk Works for about four years, but were going public to find potential partners in industry and government.

The Soviet Union had successfully used underground nuclear explosions to snuff out fires at out-of-control natural-gas wells four times in the 60s and 70s. This was just one part of a large Soviet program to use nuclear explosions for a variety peaceful ends; the U.S. had a similar yet smaller program.

In the middle of last century, out in southern Idaho, amid the sagebrush and the steppes, the Navy kept a secret site. In that place—dry and arid, far from the sea and very much unlike it—scientists and engineers simulated a nuclear-powered submarine.

A sprawling new plant here in a former soybean field makes the mechanical guts of America’s atomic warheads. Bigger than the Pentagon, full of futuristic gear and thousands of workers, the plant, dedicated last month, modernizes the aging weapons that the United States can fire from missiles, bombers and submarines.

The operator of Japan's Fukushima nuclear plant said on Thursday that 100 metric tons of highly contaminated water had leaked out of a tank, the worst incident since last August.