On March 11th 2011, a major earthquake with arecorded magnitude of 9.0 caused a giant tsunami to crash into FukushimaDaiichi Nuclear Power Plant which caused significant damage including causing manynuclear reactors to meltdown. When the earthquake hit, the nuclear reactors allautomatically shutdown, however the external power supply of the nuclearreactor was destroyed by the earthquake.
There were emergency generators inplace to provide the needed electricity that was lost, but then the tsunamiflooded these generators and caused them to fail as well as damaging theseawater pumps for both the main condenser circuits and the auxiliary coolingcircuits, such as the Residual Heat Removal cooling system. After this, thereactor operators switched to emergency battery power. The batteries weredesigned as a backup system to provide power for cooling the core for 8 hours- after8 hours, the batteries ran out, and the residual heat could no longer becarried away. In order to keep the core cool and relieve pressure levels,operators had to start venting out steam and gases. Some of the gases wereradioactive fission products, but they existed in small amounts.
Although someof these gases are radioactive, they did not pose a substantial risk to publicsafety- even to the workers on site- and were a better option than the risk ofnuclear meltdown. A Nuclear Emergency was declared, and the FukushimaPrefecture issued an evacuation order for people within 2 km of the plant and onMarch 12th the Prime Minister extended the evacuation zone to 20 km. Despite the efforts of the operators, allthree cores significantly melted in the first three days after the disaster.The nuclearaccident achieved a rating of 7 on the International Nuclear Disaster Scale (INDS)resulting from high radioactive releases between the fourth and sixth daysfollowing the event. 7 is the highest rating on the scale which puts this majoraccident on the same scale as Chernobyl. Over 100,000 people were evacuatedfrom their homes and there have been no reported deaths or cases of radiationsickness from the meltdown.
The biological effects potentially caused by thisdisaster and the release of radioactive materials are vastly unknown, however,some studies have revealed the impacts of ionizing radiation from the FukushimaDaiichi Nuclear Power Plant. One such study, on the pale grass blue butterfly, foundreduction in size, slowed growth, morphological abnormality, and high deathrate both at the contaminated site and among butterflies that were bred in alaboratory with parents collected from the site.