How did it happen (complete failure of cooling and reactors exploding)?
Although the earthquakes killed workers and wreaked havoc on the region, Japans’ nuclear plants were not compromised by the quakes. It was only the tsunami that caused Fukushima Daiichi 1, 2, & 3’s power and backup power to fail, allowing the meltdown to take place. (world-nuclearworld-nuclear.org)
Why was radioactive water released (purposely) into the ocean as stated in the article?
I found that although radioactive water was never “purposely” released into the ocean, it was known that it would likely end up there due to the failed ocean barrier wall. The water came from the necessity of cooling the overheated plants to prevent further meltdown and further contamination. The good news is that by 2012 the water within the Fukushima area was considered non-toxic to humans and aquatic species that live there. However, less is known about the effects on the ocean floor, where the radioactive matter is collecting in the sediment. (cnn.com)
What (if anything) has been done to further an international response team/plan for nuclear emergencies?
While my research turned up little results for international response development, countries have been developing their own response teams. China will have a national nuclear response team by the end of 2018 which will be made up of over 300 individuals and will meet the requirements for an international response team. This makes sense since China has more nuclear power plants than any other country in the world and expects to double its nuclear output over the next few decades. (firedirect.net)