Thursday, 17 March 2011

Major nuclear accidents around the world, What relationship & causes earthquakes & Tsunamis? Water to cool reactor in Japan!




 Major nuclear accidents around the world





BEIJING - The Fukushima No.1 nuclear power plant in northeast Japan started to leak radioactive material after an hydrogen explosion, which was caused by a devastating earthquake and ensuring tsunamis, occurred Saturday afternoon.


The following are major nuclear accidents around the world since the former Soviet Union set up the world's first nuclear power plant in 1954:


On Oct. 10, 1957, a fire broke out at the Windscale nuclear reactor (later renamed Sellafield) in northwest England, destroying the core and releasing a cloud of radioactive material. The sale of milk and other produces from nearby farms were banned for a month. Scores of people later developed cancer and died because of exposure to radiation.


On March 28, 1979, a partial core meltdown occurred at Three Mile Island in the United States due to its cooling system failure, in the most severe nuclear leak accident in the country which forced the evacuation of at least 150,000 local residents.


On April 26, 1986, the No.4 reactor at the Chernobyl nuclear plant in the former Soviet Union exploded, causing the worst nuclear disaster in history. The explosion killed 30 people on the spot, released more than eight tons of highly radioactive material, contaminated 60,000 square km of land, and caused more than 3.2 million people to be affected by radiation.


On April 6, 1993, a tank containing radioactive liquid exploded at the Tomsk-7 Reprocessing Complex in the Siberian region of Russia. A total of 10 square km of land was contaminated by radioactive material and a number of nearby villages were evacuated.


On Sept. 30, 1999, a nuclear accident occurred at a nuclear fuel plant at Tokai village, Ibaraki prefecture, Japan, killing two workers, exposing dozens of people to radiation and forcing the evacuation of local residents.


On Aug. 9, 2004, four workers were killed and seven others injured by a steam leak at the No.3 reactor at Kansai
Electric's Mihama power plant, 350 km west of Tokyo, Japan.



Relationship between earthquakes, tsunamis

BEIJING - An 8.9-magnitude earthquake struck northeastern Japan on Friday afternoon, the largest temblor ever recorded by the Japanese Meteorological Agency. The earthquake triggered a tsunami that swamped hundreds of kilometers around the epicenter.

The following is a brief introduction of the relationship between earthquakes and tsunamis.

A tsunami is a series of destructive waves, sometimes tens of meters high, caused by the displacement of a large volume of water, usually an ocean. With gigantic energy and fast movement, the waves are catastrophic to the affected coastal areas.

Tsunamis are usually triggered by earthquakes, volcanic eruptions and underwater explosions, landslides and other mass movements. Underseas earthquakes have generated nearly all the major tsunamis in history.

Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of temblor associated with the earth's crustal deformation.

When these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position.

However, undersea earthquakes do not necessarily lead to tsunamis.

Statistics from the China Earthquake Administration show that of the past 15,000 undersea tectonic earthquakes, only about 100 generated tsunamis. Some experts hold that only earthquakes of above 6.5 magnitude and with a focal depth of less than 25 km underground can cause tsunamis.

Sometimes even strong earthquakes, such as the 8.5-magnitude qukae that occurred near Sumatra in 2005, do not trigger tsunamis because the quake intensity can be largely compromised by the great focal depth, experts say.

In addition to the earthquake magnitude, global climate change may also have a bearing on the occurrence of tsunamis.

According to experts from the China Meteorological Administration, the 2004 tsunami that struck Southeast Asia was partially linked to the rising sea level caused by global climate change.


What causes earthquakes?

The earth has four major layers: the inner core, outer core, mantle and crust.

The crust and the top of the mantle make up a thin skin on the surface of our planet. But this skin is not all in one piece -- it is made up of many pieces like a puzzle covering the surface of the earth.

Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other. We call these puzzle pieces tectonic plates, and the edges of the plates are called the plate boundaries.

The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults. Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving.

Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake.

Helicopters dump water to cool reactor in Japan

TOKYO - Japan's Self-Defense Force are dumping water on the damaged No 3 reactor by helicopter following the plant's operator Tokyo Electric Power Co (TEPCO) failing to cool it sufficiently on Wednesday and Thursday.
Helicopters dump water to cool reactor in Japan
A video grab show a helicopter is dumping water on a stricken reactor in Japan to cool overheated fuel rods inside the core on March 17, 2011. [Photo/Xinhua]  
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The plan was originally shelved as it was deemed too dangerous in light of the high levels of radiation, but following the rising heat of the reactor the government decided the water drop by the helicopters would be the best way to deal with climbing hydrogen levels.

The GSDF Ch-47 helicopters can carry up to 7.5 tons of water and have also started dumping water on the No 4 reactor as well.
Meanwhile, a Tokyo police unit is primed to use a water cannon truck to cool down a spent fuel rod pool in the No 4 reactor at the quake-stricken Fukushima Daiichi nuclear power plant.

The police announced that the ground operation will involve spraying water from outside of the reactor and is due to start on Thursday morning.

Following Friday's devastating earthquake and tsunami in northeastern Japan, the temperature has been rising in the building that housing the No 4 reactor and its spent fuel storage pool, as cooling systems failed.

The building was rocked by a hydrogen explosion on Tuesday as well as a fire early on Wednesday adding to complications and raising concerns the fuel rods will melt and release radiation.

The police will aim their high pressure cannons at a hole in the wall of the damaged No 4 reactor housing structure to target the fuel storage pool.
Helicopters dump water to cool reactor in Japan
A video grab show helicopters are dumping water on a stricken reactor in Japan to cool overheated fuel rods inside the core on March 17, 2011. [Photo/Xinhua] 

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