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Fukushima sequence disaster

On Mac 12 this year, Generation II of nuclear power plant has proved it shortage of facing

nature with that lead to the explosions which happen to be at Japan Nuclear Power Plant,

Fukushima Daiichi. It was reported that 4 of 6 boiling water reactor were affected due to the

earthquake and tsunami that hit Japan. Soon after the debacle in Fukushima, the public hasgrown more nervous about anything radioactive. Fukushima Daiichi is a complex design that

has 6 boiling water reactor or BWRs as a primary system and began to operate from 1970s.

BWR in Fukushima Daiichi used Light Water Reactor as a coolant since the ordinary water is

distinguished from heavy water reactors which use deuterium oxide or D2O instead of H2O.

The person who directs the Union of Concerned Scientists Nuclear Safety, David Lochbaum

explained that his organization concern about the time taken for the cooling system to operate

back after the attack take part[www.nationalgeography.com].

The cooling system is out of control more than 72 hours and the workers were extremely

facing a challenge in getting the water to replenish into the tank. Water cannot be replenished

with fire truck or pump because the cooling system relies on active operation of the plantsown pumping system. Failure in providing electricity had cause major problem to stop the

water pump into the cooling system. Although 72 hours had been provide to get rid the

problem but it still not enough to avoid the damage it had created.[2 Josie Garthwaite,

National Geography News, news.nationalghegraphi.com, march 16].

Fukushima has its own backup system that design to handle nature disaster as earthquake and

tsunami. The backup power supplies suppose to provide power to generate pump for cooling

system. There were 3 type of power supplied in advance to help overcome this event which isexternal power supply, 2 unit diesel generator and emergency batteries. Japans already

expected this nature disasters would hit their country and build their nuclear plant with a good

safety aspect. Unfortunately, this thoughtful design cannot resist what is destiny to be.

What happened is, Fukushima Daiichi safety plan work as it should be when the disaster take

part which is automatically shutdown all the reactors. At this moment, the control rods have

been inserted into the core for the nuclear reaction stopped. At this point, the cooling system

has to remove the residual heat which is about 7% of the full power heat load under normal

operating condition [http://web.mit.edu/nse/].Unfortunately, the earthquake and tsunami come

in sequences which lead to the power failure.

When the earthquake hit, it has destroyed the external power supply that will generate backup

system to keep the coolant pump working. Without external power supply the cooling system

is not working. Then diesel generator started taking control for the first hour before largetsunami rammed the generator diesel and flooded it into failure.

One of the fundamental tenets of nuclear power plant is defense depth design.To achievereactor safety, the nuclear industry has adopted a strategy called "defense-in-depth."With this approach, a series of independent barriers are established between theradioactive material in reactors and the environment. Most of these barriers consist ofpassive, or physical design elements built to prevent the release of radioactivity.

It was applied to this 40 years nuclear plant so it can withstand severe catastrophes, but

tsunami that crashed in Fukushima was beyond all expectation. In other word, the defense

depth design not helping Fukushima Daiichi prevent it nuclear plant from rammed by naturedisaster. The generator was located 10m above sea but the tsunami that attack is 14m above

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see. This showed the weak point of Fukushima design with insufficient design against

tsunami and the generator insufficient protected against flooded.

When the diesel generators fail to execute electricity, reactors operator switched to emergency

batteries which can provide power for 8 hours. However, 8 hour the batteries ran out and the

residual heat cannot be carried out away. This is a terrified moment for every nuclear plantexists.

Without power supply to cooling down the core, operators need to use all cooling capacity to

remove the heat. To achieve it, they need to maintain the fuel rod by keeping the temperature

below 1200c and make sure the pressure at a manageable level. They also need to release the

steam which contains other gases in the reactor to the atmosphere by time to time to control

the pressure. Gases that released contains small amount of radioactive but they did not harm

to the public safety neither to the workers safety in site.

In order to keep the rod not exceed 1200 degree celcius, there were generators transport to the

site and restored some power. They even inject the sea water to ensure the rod is covered by

water. Although the reactor had been shut down, boric acid- neautron absober (contains in

sea water) is added as a conservative measure to ensure the reactor stays shut down. Boric

acid is also capable of trapping some of the remaining iodine in the water so that it cannot

escape, however this trapping is not the primary function of the boric acid.[

http://news.nationalgeographic.com]

The water used in the cooling system is purified, demineralized water. The reason to use pure

water is to limit the corrosion potential of the coolant water during normal operation. Injecting

seawater will require more cleanup after the event, but provided cooling at the time.

As reported 4 reactor was effected by earthquake and tsunami. It meant by reactor 1, 2, 3 and

4. An updated on 7 october 2011 was released by Tokyo Electric Power Company in their sitewhich mention that all the reactor have been shut up. They also give the track after the

disaster til now. They mention that reactors 1 and 3 had an explosive and release smoke. It

was assumed to be hydrogen explosion. On the other hand, reactor 4 also have an explosion

that damage the 5th floor roof top of the reactor building. [http://www.tepco.co.jp]

Chief Cabinet Secretary Yukio Edano told reporters there is a "possibility" of a meltdown at

the plants No. 1 reactor, adding, "It is inside the reactor. We can't see." He then added that

authorities are also "assuming the possibility of a meltdown" at the facility's No. 3 reactor.[

http://edition.cnn.com, By the CNN Wire Staff, March 13, 2011

How the explotion began? Hydrogen gas is extreamly combustible. So, when the fuel rod

exceed 1200 degreee celcius, it will started the reaction between zircaloy and water. This

reaction produce hydrogen gas which is extreamly combustible. As mention earlier, to

maintain the pressure in the vessel, operators had to release the gases to the atmosphere. They

believe that, the gas release contribute to the explosion when there is enough hydrogen gas

reacts with oxygen in the air. This explosion seems to occur outside of the pressure vessel. In

fact, there is possible explosion happend inside the chamber since there were no precense of

air inside the pressure vessel. Without oxygen, there will no chance hydrogen could create

explotion.

Nuclear power plant is an era of a new energy and with the world facing crisis in powerconsistency, they will trying to find solution from this incident to be repeated. The incident in

http://edition.cnn.com/http://edition.cnn.com/

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Fukushima Daiichi has have spread the doubt of having nuclear power plant. A lot of anti-

nuclear organization raising their voice for not letting any new nuclear power plant being

developt.

was note by all other country whose have nuclear power plant. Extra precaution and safety

design were applied to the future nuclear power plant. This incident did not ending the era of

nuclear power plant, but it give a new breath to it in developing technology and concept to

give better safety structure in the future.