S3A Maggy Wang

What happened?

Tsunami resulting from magnitude 9.0 earthquake damages nuclear power plant in north-east Japan.

before & after

What happened?

The plants has suffered three explosions and two fires since the crisis began Friday March 11.

What happened?

IAEA says two workers are missing at the site and at least 20 have fallen ill due to possible radiation contamination.

* IAEA International Atomic Energy Agency ( 聯合國 ) 國際原子能機構

How Japan's nuclear crisis unfolded?

How Japan's nuclear crisis unfolded?

The quake causes serious damage at Tokyo Electric Power Company's (TEPCO) Fukushima Daiichi nuclear power plant, about 65 kilometers south of Sendai.

How Japan's nuclear crisis unfolded?

But when the tsunami hits, flood water swamps the generators, causing them to fail. The reactors begin to heat up.

Reactor Basics

Reactor Basics

At the heart of a nuclear reactor is the reactor vessel, a large steel tank filled with water.

Reactor Basics

It's loaded with 12-foot-long fuel rods made of radioactive pellets encased in zirconium alloy.

鋯 Zr9140

Reactor Basics

These ceramic fuel pellets are usually made of enriched uranium 235, which is incapable of creating a nuclear explosion.

鈾 U23592

Reactor Basics

Reactor No. 3 at the Fukushima Daiichi plant used more toxic mixed-oxide (MOX) fuel rods, which contain a mixture of uranium and plutonium that is reprocessed from spent uranium.

鈾 U23592 鈽 Pu239

94

Reactor Basics

The fuel rods are loaded vertically into the reactor vessel in a precise grid pattern known as the reactor core.

Reactor Basics

Nuclear fission, or the splitting of atoms, is initiated. As each atom splits, it gives off large amounts of energy in the form of heat and radiation.

Reactor Basics

It also sends free neutrons toward other atoms, causing some of those atoms to fission. This can lead to a chain reaction.

連鎖反應

Reactor Basics

Rods that absorb neutrons control this chain reaction. When the control rods are present, neutrons are absorbed and the reaction slows. When the rods are removed, the reaction increases.

Normal operation

The speed of the chain reaction and the temperature of the fuel are also controlled by the water in the reactor vessel.

Normal operation

The heat generated by the nuclear reaction boils the water in the reactor vessel, turning the water into steam.

Normal operation

This steam flows out of the reactor vessel through pipes to steam turbines. As the steam turns the turbines, generators connected to the turbines spin and generate electricity.

渦輪機

Normal operation

The steam then travels to a condenser unit, which cools the steam, turning it back into water.

冷凝器

Normal operation

This water is pumped back into the reactor, where it is used again to control the reactor temperature and reaction speed.

Meltdown

If, however, the nuclear reaction or reactor temperature races out of control, a meltdown can occur.

* Meltdown: a serious accident in which the central part of a nuclear reactor melts, causing harmful radiation to escape 核反應堆核心熔毀（導致核輻射泄漏）

Meltdown

The fuel pellets normally operate at a temperature of 1,400 ℉

If the temperature continues to rise, the fuel rods can eventually melt. This melting can release large amounts of radiation and even vaporize the core.

( 使 ) 蒸發、汽化

The Earthquake and Tsunami

The three reactors shut down automatically in a matter of seconds when the quake struck.

The Earthquake and Tsunami

Even though the control rods were fully inserted to slow the fission chain reaction to a stop, the reactor was still extremely hot.

The Earthquake and Tsunami

This is known as decay heat, which will be present for months or even years. Cool water is still needed to keep the reactor fuel from overheating and possibly melting.

The Earthquake and Tsunami

The Earthquake and Tsunami

When the earthquake, the water pumps lost power. Emergency diesel generators began to power the pumps.

However, the tsunami that soon followed damaged the diesel generators.

The pumps then operated on emergency battery power, which lasted for 8 hours before being exhausted.

The Earthquake and Tsunami

The water pumps shut down, and workers at the plant were left with no effective way to continue to cool the reactors and prevent the fuel from melting.

The Explosions

The Explosions

The Explosions

Officials in Japan say the explosions at the three reactors were likely caused by a buildup of hydrogen gas, which is the highly flammable.

1

The Explosions

One CNN contributor suggests that some of the zirconium fuel casings in the reactor may have burst.

The zirconium can react with water to produce zirconium oxide and hydrogen. When this occurs, the hydrogen gas needs to be vented. As the hydrogen is vented and encounters oxygen in the surrounding air, the two can recombine explosively

2

The Explosions

Another theory suggests that radiation causes water in the reactor to separate into hydrogen and oxygen.

Normally, these gases would be carried away to a re-combiner that would turn them into water. But, with the lack of water circulation, the hydrogen built up until it had to be vented into the area of the building above the reactor. When enough hydrogen built up, the explosion occurred

3

Fire

Japanese officials say fire was discovered in a storage pond used for spent nuclear fuel rods in the reactor No. 4 building on Tuesday, March 15.

Exposed Fuel Rods

Helicopters began dumping massive amounts of seawater Thursday morning in order to cool the fuel pool.

Experts believe that boiling steam rising from that pool, which contains at least partially exposed fuel rods stored after being removed from the reactor, may be releasing radiation into the atmosphere.

How bad is “bad”?

Japan's Nuclear and Industrial Safety Agency raised the level for the crisis at the Fukushima Daiichi nuclear plant Friday from a 4 to 5 .

How much is “too much”?

four main types of ionizing radiation:Alpha particlesBeta radiationGamma raysX-rays

離子化的

How much is “too much”?

An average person receives about 3.1 millisieverts per year from natural sources.

Japanese officials say they had measured radiation rates of up to 400 millisieverts per hour between reactor units No. 3 and No. 4.

希弗是輻射劑量的單位， 1 希弗表每千克組織中沉積了 1 焦耳的能量。1 sievert = 1 J/kg1 希弗 =1000 毫希弗； 1 毫希弗 =1000 微希弗。

Now

WHO says there's no immediate health risk from contaminated food.

Smoke emerged from two of the damaged reactors Monday evening, officials say.

Tokyo Electric: No plans to spray mortar into damaged reactor.

灰泥

Should nuclear power be rejected?

There are three basic principles that govern the limits and utility of energy. The first two laws of thermodynamics tell us that when it comes to energy production, we cannot win, and we cannot break even.

熱力學

Should nuclear power be rejected?

We will always battle the transformation of energy from one form to another, and have it dissipated by forces beyond our control.

Should nuclear power be rejected?

But the third law is most daunting, for it states that the first two laws must proceed until all that remains is inaccessible.

In other words, if we are to survive, we have no choice but continue to play the game.

Ronald K. Chesser is director of the Center for Environmental Radiation Studies at Texas Tech University and has long researched the effects of the Chernobyl nuclear accident.

Don't be too hasty to reject nuclear power.

Source

http://edition.cnn.comhttp://www.columnpk.com/tag/ja

pan-news-in-urdu/http://www.abc.net.au/http://www.rohinews.com/