Short answers, pulled from the story.
The Fukushima nuclear accident was caused by the 9.0 magnitude Tōhoku earthquake and the tsunami that followed on the 11th of March 2011. The tsunami waves, reaching 13-14 meters, overtopped the plant's 10-meter seawall and flooded turbine and reactor buildings, destroying emergency diesel generators and backup batteries and making it impossible to cool the reactors after shutdown.
At least 164,000 residents were permanently or temporarily displaced following the accident, with that figure peaking in June 2012. Ten years later, over 41,000 people from Fukushima were still living as evacuees. The evacuation was accused of causing more harm than it prevented; 51 fatalities were attributed to the evacuation itself, primarily among hospital patients and elderly nursing home residents.
Residents near the accident site received an estimated 12-25 millisieverts of radiation exposure in the year following the accident. The United Nations Scientific Committee on the Effects of Atomic Radiation found no adverse health effects among Fukushima residents directly attributable to radiation exposure. Insurance compensation was paid for one plant worker's lung cancer death, though no causal link to radiation was established, and six other people were reported to have developed cancer or leukemia.
Before the accident, nuclear power supplied over 25 percent of Japan's domestic electricity. All nuclear reactors in the country were shut down by 2013, reducing nuclear's share to less than one percent. Japan revised its greenhouse gas reduction target from a 25 percent decrease below 1990 levels to a 5.2 percent emissions increase by 2020. Fossil fuel imports increased so sharply that Japan ran a trade deficit for the first time in decades.
Three investigations concluded the accident was man-made and foreseeable. The NAIIC, the first independent investigation by Japan's National Diet in 66 years, found that TEPCO and the government failed to meet basic safety requirements and that the accident had roots in "regulatory capture" and a culture of obedience and reluctance to question authority. On the 12th of October 2012, TEPCO admitted it had failed to take necessary safety measures out of fear of lawsuits and public protests.
Plant management estimated the full decontamination and decommissioning program will take 30 to 40 years from the accident. TEPCO plans to remove all fuel rods from spent fuel pools in units 1, 2, 5, and 6 by 2037, and to extract molten fuel debris from reactor containments in units 1, 2, and 3 by approximately 2050. Japan's trade ministry estimated the total cost at 20 trillion yen, equivalent to 180 billion US dollars, as of November 2016.