The Fukushima Daiichi nuclear power plant disaster was a meltdown of its three cores on March 11, 2011. The meltdown lasted three days. An earthquake followed by a 15-meter tsunami damaged the power supply and cooling system of the plant on the same day. The International Nuclear Event Scale gave a ranking of 7 for the tragedy.
Fukushima-Blog.com
March 11
Near Honshu, Japan, an earthquake with a magnitude of 9 striked. A 15-meter tsunami followed. Electricity was knocked out at the Fukushima Daiichi plant. Diesel generators cooled reactors 1, 2, and 3 by pumping water. They were shortly stopped by flooding. Within the reactors, water began to boil and the water level dropped. Pressure rose. The water level stayed above the fuel components.
March 12
Unit 1 experienced a pressure of 840 kPa, double the standard level. Steam was vented out to attempt to lower the buildup, but some radioactive material was inevitably released. Unit 1 exploded, releasing hydrogen gas. Potassium iodine tablets were ready to be used by workers to protect against iodine-131 from entering the body. A 20-km evacuation radius was placed around the site. Seawater and boric acid were filled into structures surrounding the reactor.
March 13
Steam was vented from Unit 3 to control buildup. All three reactors had dropping water levels. Injection of seawater into the plant began.
March 14
Mobile generators powered all reactors. A crew injected seawater and boron into Unit 1. Unit 2 was cooled through core isolation. A hydrogen explosion occurred at Unit 3. Radioactive material was blown out to sea by winds. Cold shutdown status was given to Units 1, 2, and 3.
March 15
Radiation levels dropped off. A fire broke out at Unit 4 from a pond of fuel storage. Radioactive material at doses of 400 millisieverts per hour was recorded as it traveled straight into the atmosphere.
March 16
Unit 3's pressure dropped. Unit 5's water level dropped. Fuel pools were rising to dangerous temperatures. At least 17 people experienced radiation exposure and two were missing.
March 17
Helicopters dropped water on Unit 3's used fuel rods, which contained plutonium-239. A power cable was connected to Unit 2.
March 18
Fallout reached California. The radiation levels were significantly below concerning levels.
March 19-20
Units 1, 2, and 3 were sprayed with seawater. Unit 1's containment structure was intact and pressure was stable. Units 2 and 3 were believed to have damaged vessels. The fuel pools of Units 3 and 4 were dangerously hot. Helicopters dumped water on them. Units 5 and 6 began to warm up. Water was pumped through them and the roofs were drilled with holes to prevent explosions. The Japanese government recommended citizens nearby to take iodine pills, as dangerous radioactive iodine-131 was found in milk and crops.
March 21
The containment structures of Units 2 and 3 were intact. Units 1 and 2 were about to receive power, and Units 3 and 4 already began receiving power.
March 22
Unit 2's fuel pools were rising in temperature. The power lines connecting to Units 1 and 4 may have been compromised, so that problem was being fixed. Water was continued to be sprayed onto other Units. Seawater near Fukushima was detected to contain high concentrations of iodine and cesium. The Japan Agency for Marine-Earth Science and Technology began sampling of seawater. 25 miles from the plant, radiation levels 400 times higher than normal were detected.
March 23
Efforts to restore plant power were under way. Iodine-131 was detected at 210 becquerels per liter in Tokyo, below the 300 becquerel limit for adults, but above the 100 becquerel limit for babies. Near Fukushima, shipping of contaminated vegetables ended.
March 24
In Tokyo, levels of radioactive iodine dropped to a safe level of 79 becquerels per liter. All six Units were being sprayed with water, but the most troublesome one, Unit 2, rose to 47 degrees Celsius. 17 workers received exposures greater than 100 millisieverts.
March 25
The 12-mile radius of evacuation is enforced. Unit 3, a reactor that utilizes threatening uranium and plutonium, was damaged. Testing of the thyroids of children led to no serious problem. Three workers traveled to a hospital for radiation sickness. Seawater was injected into Units 1, 2, and 3, and Unit 4 was being sprayed with seawater.
March 26-27
Workers switched from seawater to freshwater to pump into the Units. The temperatures and pressures of Units 1, 2, and 3 stabilized. Units 5 and 6 remained shut down. All six Units were connected to power. Gamma radiation doses in Tokyo ranged from 0.08 to 0.15 microsievert per hour, up to slightly above recommendations. 30-41 km from Fukushima, doses ranged from 0.9 to 17 microsievert per hour, higher than normal.
March 28
Efforts to restore electricity to the reactors began with draining water from the turbines. However, in Unit 2's turbine building, radiation doses of 1,000 millisieverts per hour were detected (four times the yearly limit for workers). Units 1 and 3 were draining contaminated water. A mile north of the drainage tunnels of Units 1, 2, 3, and 4, an agency found iodine-131 concentrations 1,150 times the allowed limit. No fishing has been allowed near the area.
March 29
The situation remained serious. The challenge of restarting power production remained daunting. Workers must remove and store sprayed water. Near the plant, soil samples indicated traces of plutonium.
March 30
Units 1, 2, 3, and 4 will have to be abandoned due to their heavy damage. Before this can occur, workers will have to cool spent fuel and store contaminated water to restore original cooling systems.