15 March 2011

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Understand Nuclear Meltdown what is Nuclear meltdown? What is Risk?

Understand Nuclear Meltdown what is Nuclear meltdown?
What is Risk?

Keywords, Tags – Nuclear Meltdown, Nuclear Meltdown Risk, Partial Meltdown, Full nuclear meltdown,Potassium Iodine Tablets Japan

Currently partial meltdown of nuclear fuel rods has occurred in three or two nuclear reactors at the Fukushima Daiichi power plant in Japan.

Definitions of nuclear meltdown –

The melting temperature of uranium dioxide is 5,189 degrees Fahrenheit (2,865 degrees Celsius)
uranium dioxide fuel rods are maintained at a temperature below their melting point.
"A meltdown is when the uranium dioxide fuel melts.
The term nuclear meltdown is not officially defined by the International Atomic Energy Agency or by the U.S. Nuclear Regulatory Commission.

Generally Nuclear meltdown is defined as overheating of the core of a nuclear reactor resulting in the core melting and radiation spreads.

When meltdown occurs radioactive materials could be released into the environment.
A core damage accident is caused by the loss of sufficient cooling for the nuclear fuel within the reactor core.

Meltdown is considered very dangerous situation as radioactive materials are released into the environment.
The term Meltdown refers to melting of the fuel in the reactor.

The plants at Fukushima are so called Boiling Water Reactors or BWR for short.
Boiling Water Reactors are similar to a pressure cooker.

The nuclear fuel heats water, the water boils and creates steam, the steam then drives turbines that create the electricity, and the steam is then cooled and condensed back to water, and the water send back to be heated by the nuclear fuel.

The nuclear fuel is uranium oxide with very high melting point of about 3000 °C.
The fuel is made in small brick like cylinders.
Then these are put into a long tube made of Zircaloy with a melting point of 2200 °C, and sealed tight.
The assembly is called a fuel rod.

The Zircaloy casing is the first containment. It separates the radioactive fuel from the rest of the world.
These fuel rods are then put together to form larger packages,
And a number of these packages are then put into the reactor.

All these packages together are referred to as “the core”.
The core is then placed in the “pressure vessels”.
The pressure vessel is the second containment.

The entire “hardware” of the nuclear reactor is encased in the third containment which is
Air tight very thick bubble of the strongest steel.

The purpose of the 3rd containment is to keep the core always and permanently cool.

This third containment is then surrounded by the reactor building.
The reactor building is an outer shell that is supposed to keep the weather out

Uranium contains unstable atoms, which spontaneously split into smaller atoms.
Subatomic particles are emitted that carry away energy.
This process is called radioactive decay.

Nuclear reactor power is derived from the fission chain reaction.

When uranium is collected together, the atoms cause a chain reaction.
The particles hit each other causing them to split and emit more particles; this continues this process is called as fission.
This process releases heat and blue glow called as Cherenkov radiation.

To slow down reaction of uranium in reactor a material such as graphite can be inserted into mass of radioactive material in order to slow down the reaction, to control the reactions.

What is core?
The uranium fuel rod assembly is called as core.
The core is kept in water to keep in cool and it also helps to control nuclear fission reaction.
With water the control rods are also inserted to control the reaction.

Because of some accident natural or human made if water circulation stops then the cooling system will stop.
After some time cooling water starts to boil in sealed containment vessel, pressure rises as there is no way to escape.

Here Consider pressure cooker which we use for making rice in that Pressure Cooker if water is kept boiling with no escape what will happen?

Now a day’s nuclear reactor gets shutdown automatically but even if reactor is turned off then also radioactive fission continue to produce heat.
These radioactive fission products are normally contained in the intact fuel elements and their heat generation decreases with time.

This is reason cooling is very important for reactors.

When reactor is shut down, water pumps not working the core keeps heating until the fuel rods melt.

As they start to melt radioactive materials may get released into the reactor vessel and containment building and environment.

Partial meltdown is where partial or say not complete core is uncovered.
When core is completely uncovered its called as full meltdown.

If adequate cooling is re-established at a partial core melting state, the reactor damage and additional discharge of fuel radioactivity content to the environment could be limited
Thus damage also gets limited.

Potassium Iodine Tablets and Radiation? Are they anti radiation?
It has been reported that Japan has distributed potassium iodine tablets to residents who may have been exposed to radiation from the nuclear power plants
Potassium iodine, or what’s known as KI, “is not an ‘anti-radiation’ drug
According to the U.S. Nuclear Regulatory Commission Potassium iodide helps protect against thyroid cancer a major risk following radiation exposure by reducing the amount of radioactive iodine absorbed by the thyroid gland
It doesn’t protect other organs, and it doesn’t protect against other radioactive materials.

Dr. David J. Brenner, director of the Columbia University’s Center for Radiological Research said to NY time’s iodine pills were protective, but were “a bit of a myth” because their use is based on the belief that the risk is from inhaling radioactive iodine. Actually, he said, 98 percent of people’s exposure comes from milk and other dairy products.

“The way radioactive iodine gets into human beings is an indirect route,” he said. “It falls to the ground, cows eat it and make milk with radioactive iodine, and you get it from drinking the milk. You get very little from inhaling it. The way to prevent it is just to stop people from drinking the milk.”

Reality views by sm –
Tuesday, March 15, 2011


Teamgsquare March 15, 2011  

nice piece of information.

SM March 15, 2011  

Team G Square,

Rama Ananth March 15, 2011  

There seems to be no end to the trauma unleashed by God and man.

sm,  March 15, 2011  


Irfanuddin March 15, 2011  

After Tsunami Situation is really very serious there as far as Nuclear Leakage is concerned ....

sm,  March 15, 2011  


OtienoHongo March 17, 2011  

Great piece of information. We read /hear these terms on the news and regurgitate them without understand what we are really talking about.

sm,  March 17, 2011