In March 2011, Japan was hit by a devastating tsunami killing 20,000 and triggering a nuclear meltdown. Survivors and witnesses tell their extraordinary stories.

Concluding the two-part documentary about the 2011 earthquake in Japan which triggered a meltdown at the Fukushima Daiichi Nuclear Power Plant. Here, nuclear experts explain what went wrong at the power plant. Among the many contributing factors, two of the most critical were also the most shockingly simple.