Uh-oh, Japan, this is bad

[Hosakawa Tito]

Japan is well known for disaster preparedness and it's strict building codes. They've spent billions over the years to develop and use technologies to limit the damage from earthquakes & tsunamis. The death toll will probably be lower because of this effort and foresight, but it really is shocking how puny our efforts can be compared to the natural forces that drive this planet.

[Xiahou]

I wonder why the reactors weren't SCRAM'ed once the quake hit?

[Beskar]

I wonder why the reactors weren't SCRAM'ed once the quake hit?

The quake damaged the equipment to do that.

[Cute Wolf]

a very tragic event, I just hope everything will be ok and not much damage is done. My pray for you as well

[Louis VI the Fat]

My condolences to all.


As Japan braces itself for a second quake, another nuclear plant has lost its cooling system.

This does little to promote nuclear energy. We may have to rethink its proliferation. You can build them with the latest safety measures, with the physics guaranteeing thast these new reactors are 100% safe, guaranteed!, but apparantly nuclear plants simply have a tendency to blow up.

[gaelic cowboy]

This does little to promote nuclear energy. We may have to rethink its proliferation. You can build them with the latest safety measures, with the physics guaranteeing thast these new reactors are 100% safe, guaranteed!, but apparantly nuclear plants simply have a tendency to blow up.

Yea I suppose we should ban Nuke power due to all the 8.9 earthquakes we get in France every year.

[rory_20_uk]

Look at the number of explosions of nuclear plants.

Look at the number of explosions at oil refineries - without 8.9 quakes causing them.

Nothing is 100% safe. As yet there has been little more than a minor leak and no one has died. Compared to other causes of deaths in the world there are more important things to be worrying about banning.

[lars573]

My condolences to all.


As Japan braces itself for a second quake, another nuclear plant has lost its cooling system.

This does little to promote nuclear energy. We may have to rethink its proliferation. You can build them with the latest safety measures, with the physics guaranteeing that these new reactors are 100% safe, guaranteed!, but apparently nuclear plants simply have a tendency to blow up.

Yes when they are hammered by 2 big earthquakes within a day of each other and the resultant tsunami. You have to realize that all large scale electrical generation not using moving water uses steam. A nuclear reactor replaces burning fossil fuels with Uranium/plutonium to heat the water into steam. Thing about steam is that it has a tendency to cause explosions when it goes uncontrolled.


Also the Fukushima I facility has 6 reactors. Unit 1 is what blew, unit 3 was/is in danger of going the same way. Those are the ones being filled with sea water and boric acid. Fukushima II SCRAM'ed as soon as the power went out.

[Tellos Athenaios]

This isn't a steam pressure problem. This is an energy transfer from the reactor into steam which isn't kept moving which means that locally so much energy is “stored” in the steam that the bonds of the atoms from the water molecules in the steam are dissolved and the elements separated. This creates hydrogen and oxygen, which rises to the top of the structure (having a lesser density than steam). Away from this energy source (heat emitted from the core) these elements react into water again, i.e. ignition of the hydrogen gas. The energy required to split the water molecules is released as it were, and since nearly all hydrogen will react with the oxygen within the smallest timeframe, the resulting explosion is very powerful.

Now this danger is fairly unique to BWR reactors, because the temperature and the pressure required to make the steam absorb so much energy and then this energy to make the molecules disintegrate into their component elements is a combination of factors that you don't get much elsewhere. In fact to produce hydrogen you typically need to resort to electrolyse, but this is a much more controlled reaction (and once the power is cut the reaction stops). Since hydrogen is most often undesired (because it is so dangerous in the presence of oxygen) research goes into substitutes for hydrogen producing solutions to avoid it entirely.

[Husar]

The quake damaged the equipment to do that.

In any reactor, a SCRAM is achieved by a large insertion of negative reactivity. In light water reactors, this is achieved by inserting neutron-absorbing control rods into the core, although the mechanism by which rods are inserted depends on the type of reactor. In PWRs, the control rods are held above a reactor's core by electric motors against both their own weight and a powerful spring. Any cutting of the electric current releases the rods. Another design uses electromagnets to hold the rods suspended, with any cut to electric current resulting in an immediate and automatic control rod insertion. A SCRAM rapidly (less than four seconds, by test on many reactors) releases the control rods from those motors and allows their weight and the spring to drive them into the reactor core, thus halting the nuclear reaction (by absorbing neutrons) as rapidly as possible. In BWRs, the control rods are inserted up from underneath the reactor vessel. In this case a hydraulic control unit with a pressurized storage tank provides the force to rapidly insert the control rods upon any interruption of the electric current, again within four seconds. A typical large BWR will have 185 of these control rods. In both the PWR and the BWR there are secondary systems (and often even tertiary systems) that will insert control rods in the event that primary rapid insertion does not promptly and fully actuate.

Seems pretty weird, guess the spring from above method is better than the pressure tank from below method then?
I also wonder why noone on any news I've seen mentioned that the mechanics for the control rods had failed, they all sound like the cooling system was/is the only problem here with no other way to keep the reactors cool.
Then there is the issue of the batteries and the emergency generators being apparently the only way to power the cooling system, one expert mentioned that our reactors here have those, plus a way to attach external generators that can be brought in from elsewhere, which makes a lot of sense.

I don't think this shows why nuclear energy is bad and shouldn't be used at all as some are screaming, I think it shows why more money should be invested into it to think about how we can use it safely, and yes, that means it should be possible to replace a lot of the vital parts with ones brought in from outside and why the emergency systems should be kept very simple or at least have very simple, manual secondary controls. Oh and perhaps why BWRs should actually be phased out ASAP.

That said it's a really tragic event that seems to have spawned more tragic events, I'm sorry for the Japanese and wish them the best for their way through and out of this.

[lars573]

Some perspective from a physicist:
why i am not worried about japans nuclear reactors/

He posits that the explosion at Fukushima I unit I was caused by super heated and irradiated steam being pumped into the reactor building, but fully outside the reactors outer concrete layer, to relieve pressure inside the reactor. But that it was so hot that it actually broke the hydrogen bonds* in the water and it separated into pure hydrogen and oxygen. And both being highly volatile and explosive gases, they went up.




*Having taken chemistry in high school I know that to be no mean feat. Hydrogen bonds are among the strongest in nature.

[Banquo's Ghost]

I've been watching the news of this disaster with increasing horror as we see more and more of the devastation revealed. The scenes from Minami Sanriki are cataclysmic - reminiscent of the photographs of Hiroshima after the bomb. Nothing stands. A town of 17,000 people is mud and sticks. Perhaps 10,000 of those people have also been obliterated.

There is a film taken of the wave - a black, roiling creature of demonic power that simply arrives and overwhelms the things of Man, unstoppably brutal. And I am reduced to tears by the pictures of a tired man staggering into yet another shelter on his seemingly endless search for his family, shoulders slumped under the increasing weight of his hopelessness, only for a shriek of recognition to herald his wife grabbing him in a hug. The happiness and relief was so poignant that I could no longer watch the screen - and how many will not find joy, but only the scant consolation of a mortuary slab, or worse, nothing but memories.

[Togakure]

Here is a link to a series of before-and after photos of areas hit by the tsunami. Draw your mouse across the "before" images from left to right to see the "after" image. Hard to imagine being in the middle of something like this.

http://www.abc.net.au/news/events/ja...eforeafter.htm