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1. Fukushima Daiichi Nuclear DisasterThe massive earthquake and tsunami that struck Japan's northeast coast on March 11, 2011, triggered a nuclear crisis of proportions unseen since the Chernobyl meltdown of 1986. After electricity was lost, flooding destroyed the crucial backup generator to run the cooling system needed to control the decay heat of the nuclear fuel at the coastal Fukushima Daiichi Nuclear Power Station.

(Related: "Japan Reactor Crisis: Satellite Pictures Show Damage")

(Related Quiz: Energy News 2011)

Within hours, hydrogen buildup sparked explosions, and with outer containment lost and partial meltdown inside three of the six reactors, workers began a weeks-long epic struggle to bring Fukushima under control. (Related: "A Rare Look Inside Fukushima Daiichi")

The accident transformed not only the immediate energy landscape of Japan, but also the long-term energy plans of countries all over the world. (Related: "Energy Short Japan Eyes a Renewable Future") At the start of 2011, nuclear energy was said to be on the cusp of a "renaissance." Fukushima Daiichi slammed the brakes on that movement.

Germany shut down eight of its 17 nuclear reactors within days of the tsunami, and soon the country decided to ditch nuclear entirely by 2022. European engineering firm Siemens said in September that it would exit the nuclear power plant business. In India, protests against plans to build the world's largest nuclear plant widened after Fukushima, but the government has insisted that nuclear will be necessary to meet its goals for expanding electricity access and limiting greenhouse gas emissions.

At year's end, conditions inside Fukushima Daiichi have stabilized, but Japanese officials face a host of challenges ranging from radioactive decay inside the reactor to hot spots detected far from the restricted zone. Here, radiation experts dispatched by the International Atomic Energy Agency in October examine Unit 3.

(Related: "India Maps Out a Nuclear Future, Amid Opposition")

(Related: "Is Armenia's Nuclear Plant The World's Most Dangerous?")

—Josie Garthwaite
Photograph courtesy Giovanni Verlini, IAEA

Pictures: Top Energy Stories of 2011

It was a year of shattered faith in nuclear power, and in the West, eroding support for renewables. But the East's relentless growth shaped the world of energy in 2011.

December 1, 2011