With contaminated water from Japan’s crippled Fukushima nuclear complex continuing to pour into the Pacific, scientists are concerned about how that radioactivity might affect marine life. Although the ocean’s capacity to dilute radiation is huge, signs are that nuclear isotopes are already moving up the local food chain.

The world’s worst nuclear reactor mishap in 25 years was caused by a massive natural calamity but compounded by what appear to be surprising mistakes by Japanese engineers. The result has been a fast-moving disaster that has left officials careening from one emergency to the next.

A leading U.S. expert on nuclear energy discusses some of the fundamental failures that led to the intensifying nuclear drama in Japan and looks at what might lie in store for nuclear power worldwide.

The disaster at the Fukushima-Daiichi nuclear power plant has highlighted the importance of nuclear energy to Japan and the power long wielded by the nuclear sector. But that influence now is sure to wane, to the relief of opponents who have fought for years to check nuclear's rapid growth.

To shift the global economy from fossil fuels to renewable energy will require the construction of wind, solar, nuclear, and other installations on a vast scale, significantly altering the face of the planet. Can these new forms of energy approach the scale needed to meet the world’s energy demands?

The U.S. has invested billions of dollars trying to create a controlled form of nuclear fusion that could be the energy source for an endless supply of electricity. But as a federal laboratory prepares for a key test, major questions remain about pulling off this long-dreamed-of technological feat.