It triggered a tsunami which swept over the main island of Honshu, killing more than 18, people and wiping entire towns off the map. At the Fukushima nuclear power plant, the gigantic wave surged over defences and flooded the reactors, sparking a major disaster.
Authorities set up an exclusion zone which grew larger and larger as radiation leaked from the plant, forcing more than , people to evacuate from the area. A decade later, that zone remains in place and many residents have not returned. Authorities believe it will take up to 40 years to finish the work, which has already cost Japan trillions of yen. It sits on the country's east coast, about km miles north-east of the capital Tokyo.
On 11 March at local time GMT the earthquake - known as the Great East Japan Earthquake, or the Tohoku earthquake - struck east of the city of Sendai, 97km north of the plant. Residents had just 10 minutes warning before the tsunami hit the coast. Overall almost half-a-million people were forced to leave their homes as a result of the earthquake, tsunami and nuclear accident. Systems at the nuclear plant detected the earthquake and automatically shut down the nuclear reactors.
Emergency diesel generators turned on to keep coolant pumping around the cores, which remain incredibly hot even after reactions stop. But soon after a wave over 14 metres 46ft high hit Fukushima.
The water overwhelmed the defensive sea wall, flooding the plant and knocking out the emergency generators.
Workers rushed to restore power, but in the days that followed the nuclear fuel in three of the reactors overheated and partly melted the cores - something known as a nuclear meltdown. The plant also suffered a number of chemical explosions which badly damaged the buildings. Radioactive material began leaking into the atmosphere and the Pacific Ocean, prompting the evacuations and an ever-widening exclusion zone. There were no deaths immediately during the nuclear disaster.
At least 16 workers were injured in the explosions, while dozens more were exposed to radiation as they worked to cool the reactors and stabilise the plant. Three people were reportedly taken to hospital after high-level exposure. Long-term effects of the radiation are a matter of debate. The World Health Organization WHO released a report in that said the disaster will not cause any observable increase in cancer rates in the region. Scientists both inside and outside Japan believe that aside from the region immediately around the plant, the risks of radiation remain relatively low.
On 9 March , ahead of the year anniversary, a UN report said there had been "no adverse health effects" documented among Fukushima residents directly related to the radiation from the disaster. Any future radiation-related health effects were "unlikely to be discernible", it said. But many believe the dangers are far greater, and residents remain wary.
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Don't have an account? Type : Nuclear power plant. Location : Ohkuma, Japan. Capacity : MW. Number of Units : Six. Current Status : Closed. Period of Operation : Units two, three, four and five had MW installed capacity each.
Units two and three were commissioned in and respectively, whereas units four and five were brought into operation in The unit six, with an installed capacity of 1,MW, was commissioned in The containment structure for units 1 to 5 was of Mark I configuration, whereas unit six featured Mark II containment structure.
The unit one reactor core contained fuel assemblies, while the units two, three, four and five were operated with fuel assemblies, whereas the unit 6 reactor core contained fuel assemblies. The function of the primary containment system is to contain the energy released during any loss of coolant accident LOCA of any size reactor coolant pipe, and to protect the reactor from external assaults. During normal operation, the dry containment atmosphere and the wetwell atmosphere are filled with inert nitrogen, and the wetwell water is at ambient temperature.
A small amount of hydrogen is routinely formed by radiolytic decay of water, and this is normally dealt with by recombiners in the containment vessel. They would be insufficient for countering major hydrogen formation due to oxidation of zirconium fuel cladding.
Apart from this, at low containment pressures hydrogen and other gases are routinely vented through charcoal filters which trap most radionuclides. If a LOCA occurs, steam flows from the dry containment drywell through a set of vent lines and pipes into the suppression pool, where the steam is condensed. Steam can also be released from the reactor vessel through the safety relief valves and associated piping directly into the suppression pool.
Steam will be condensed in the wetwell, but hydrogen and noble gases are not condensable and will pressurise the system, as will steam if the wetwell water is boiling. In this case emergency systems will activate to cool the wetwell, see below. Excess pressure from the wetwell above kPa can be vented through the m emission stack via a hardened pipe or into the secondary containment above the reactor service floor of the building.
Less volatile elements in any fission product release will plate out in the containment. The secondary containment houses the emergency core cooling systems and the used fuel pool. It is not designed to contain high pressure. The primary cooling circuit of the BWR takes steam from above the core, in the reactor pressure vessel, to the turbine in an adjacent building.
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