The U.S. Nuclear Regulatory Commission says American nuclear plants need to be better prepared for the sudden and continued loss of electric power. Above, the Limerick Generating Station, a nuclear power plant in Pottstown, Pa. Stan Honda/AFP/Getty Images hide caption
Workers at the Fukushima Dai-ichi nuclear power plant spray a substance to help reduce dust on April 1. Experts say it's likely that workers at the plant could have reduced the severity of the accident if they had made different decisions during the crisis. TEPCO hide caption
This March 24 aerial photo shows the extent of damage at the Fukushima Dai-ichi nuclear power plant in Japan. The 40-foot-tall tsunami destroyed the electrical and cooling systems, resulting in meltdowns at some of the reactors. Air Photo Service/AP hide caption
Workers at the Fukushima Dai-ichi nuclear power plant spray a substance to help reduce dust on April 1. The cleanup operation at the facility could take more than a decade. TEPCO hide caption
Manholes poke out from the ground in Urayasu, Japan, due to the liquefaction triggered by the 9.0 magnitude earthquake. The phenomenon, which allows sand and water to rise following ground shaking, was particularly pronounced in this area as a result of the long duration of the March 11 quake. Koki Nagahama/Getty Images hide caption
TEPCO workers spray synthetic resin over the ground at the plant to prevent radioactive dust from spreading beyond the premises. AP hide caption
In November 1940, just months after its completion, a large section of the Tacoma Narrows Bridge crashed into Puget Sound in Tacoma, Wash. The bridge collapsed under high winds — a failure that shocked engineers at the time. AP hide caption
A TEPCO employee points at a crack discovered April 1 in a maintenance pit on the edge of the Fukushima Dai-ichi nuclear nuclear power plant in northeastern Japan. AP hide caption
Japan Self-Defense Force officers in radiation protection suits hold a blue sheet over patients who were exposed to high levels of radiation at the Fukushima Dai-ichi nuclear power plant on March 25. A team of experts at Japan's National Institute of Radiological Sciences have helped treat injured workers. Jiji Press/AFP/Getty Images hide caption
A power station worker monitors one of the reactors in the control room of England's Oldbury Nuclear Power Station in 2006. Matt Cardy/Getty Images hide caption
Cows that consume feed, grass or water contaminated with radioactive iodine-131 can concentrate the element in their milk. Peter Elvidge/iStockphoto.com hide caption
The facilities at the Fukushima Dai-ichi nuclear power plant were designed to withstand strong earthquakes and tsunamis, but not to the strength and size experienced on March 11. Air Photo Service/AP hide caption
Japanese Buddhist monk Tanaka Tokuun, who was evacuated from Fukushima prefecture, looks over an instrument measuring radiation levels at a hotel on March 17. Buddhika Weerasinghe/Getty Images hide caption
A Tokyo Electric Power Co. worker looks at gauges in the control room for Units 1 and 2 at the Fukushima Dai-ichi plant, Wednesday. AP Photo/Nuclear and Industrial Safety Agency hide caption
Many of the sensors and cameras at the nuclear power plant were disabled by explosions, so plant operators are turning to highly maneuverable robots to get a better idea of what's going on in areas where it's far too radioactive for workers to venture. iRobot hide caption
