Gill A. Pratt in the Bulletin of the Atomic Scientists:
On March 12, 2011—the day after a powerful earthquake and tsunami struck the Fukushima Daiichi Nuclear Power Station—a team of plant workers set out to enter the darkened reactor buildings and manually vent accumulated hydrogen to the atmosphere. At first, the workers made progress inside the buildings, but soon their dosimeters showed they had reached their maximum emergency radiation exposure limits, and they had to turn back. In the days that followed, with vents still closed, hydrogen built up in each of three reactor buildings, fueling explosions that extensively damaged the facility, contaminated the environment, and drastically complicated stabilization and remediation of the site.
News of the earthquake galvanized those in charge of robotics programs at the US Defense Advanced Research Projects Agency (DARPA). Humanitarian assistance and disaster relief is a primary mission of the Defense Department, and DARPA had responded to a disaster before, sending robots whose development it had funded to New York City in the days after the 9/11 attacks. The robots found no survivors then, but perhaps this time, robots could help mitigate the evolving disaster.