Japanese Tsunami

[Dowly]

I've heard the culture is pretty much so that everyone tries not to draw attention to themselves.

[Platapus]

Originally Posted by UnderseaLcpl

Semantics. But thanks for explaining.

Not just semantics. With the control rods under the reactor it takes some power to raise them. Electric power or hydraulics but in any case power. And if the power supply is damaged or interrupted, it is hard to move the control rods. That is one of the weaknesses of BWR. With PWR reactors, the rods come down and can be "powered" by gravity in an emergency.


[/quote] If we knew that, why wasn't the reactor designed with more control rods, or why wasn't there a system installed to dump non-fissile materials into the core in the event of a power failure? Why not simply place a container full of dirt over the core that will release its contents upon loss of electrical current? I'm oversimplifying for the sake of brevity but you know what I mean, right? [/quote]

All great points, but remember these are commercial power plants. Someone has to pay for each engineering "improvement".

While it would be nice to think that safety to the public has no price, but it does. There is a limit on the expense. It is possible to design and build a nuclear reactor that is as close to 100% safe as possible. The problem is that it won't be able to generate enough electricity to pay for itself. Nuclear reactors are very expensive to build.

Then why design a system that would allow temperatures to increase to that point in the first place without flooding the reactor with neutron-absorbing materials? I figure I'm either missing something here or GE went ahead and designed a system that they knew was not failsafe...or perhaps they are simply incompetent.

I don't think they were either. It is very hard to design a nuclear reactor what would "fail safe" and still be capable of producing electricity on a commercial level. Remember that vast majority of nuclear reactors that have ever been produced have operated without any incident.

I would favourably compare the safety record with nuclear reactors with the safety record with hydro dams (they fail) and TPPs (they explode and burn). Nuclear reactors are actually pretty safe. They are similar to commercial aircraft accidents, they don't happen often, but when they do, they are pretty bad and hence newsworthy.

http://www.world-nuclear.org/info/inf06.html

One question that I do have, which meshes with your concerns is the lack of safety rods. I would like to know why these reactors were not equipped with safety rods.

Control rods are used to control the fission. Safety rods are used to completely stop the fission in an emergency. If I were king, I would insist that all reactors have a system of independent safety rods capable to halting the fission despite any void coefficient changes.

But that costs money, and it is hard to justify the money to prevent something that rarely happens.

Look at commercial airliners. Why did they change from seats rated for 9gs for seats rated for 6g even though studies show that seats need to be able to withstand more than 6g in an accident?

Or why did the airlines remove the locking armoured cockpit door in the 1990's?

Because the risk did not justify the cost. Or more accurately, the probability of the risk did justify the certainty of the cost.

[razark]

Originally Posted by Platapus

Not just semantics. With the control rods under the reactor it takes some power to raise them. Electric power or hydraulics but in any case power. And if the power supply is damaged or interrupted, it is hard to move the control rods. That is one of the weaknesses of BWR. With PWR reactors, the rods come down and can be "powered" by gravity in an emergency.

Some co-workers and I were discussing this earlier. Why would the reactor be designed like this? The safety factor of being able to drop the control rods in an emergency would seem to outweigh any need for having them rise from the bottom.

Also, would the control rods be able to be raised by an automatic system, such as a spring, with the control system actively holding them back?

[Skybird]

Originally Posted by razark

Some co-workers and I were discussing this earlier. Why would the reactor be designed like this? The safety factor of being able to drop the control rods in an emergency would seem to outweigh any need for having them rise from the bottom.

Also, would the control rods be able to be raised by an automatic system, such as a spring, with the control system actively holding them back?

German Die Welt reports that the two chief designers of the reactor admitted that nobody took into account the possibility of earthquakes beyond 8.0 or tsunamis, and that instead they just copied design plans by General Electric without thinking a second thought about it.

http://www.welt.de/vermischtes/artic...spanne-zu.html

Die Konstrukteure hätten im Wesentlichen Pläne der US-Firma General Electric kopiert, sagte der Ingenieur. Die darin vorgesehenen Sicherheitssysteme seien aber nicht für ein Tsunami-gefährdetes Kraftwerk konzipiert gewesen. Trotzdem habe man die Konstruktion fast eins zu eins übernommen. "Wir waren nah dran, ignorant zu sein. Wir haben nicht geprüft, ob die vorgesehenen Maßnahmen ausreichten“, sagte Oguro.

[ASWnut101]

Originally Posted by UnderseaLcpl

If we knew that, why wasn't the reactor designed with more control rods, or why wasn't there a system installed to dump non-fissile materials into the core in the event of a power failure? Why not simply place a container full of dirt over the core that will release its contents upon loss of electrical current? I'm oversimplifying for the sake of brevity but you know what I mean, right?

Well first, the reactor is normally full of water and steam under very high pressures (around 950-1000 psi). Trying to drop large amounts of any loose material would be very difficult due to the pressure differential, and the fact that liquid water is flowing upwards through the core would mean little "dirt" would actually reach the core and stay there.

Second, BWRs have a steam dryer directly above the reactor core. This is the primary reason why the control rods are inserted from the bottom, as there's a bunch of crap blocking insertion from above. It would also have the effect of blocking any safety material dropped from the top.

Then why design a system that would allow temperatures to increase to that point in the first place without flooding the reactor with neutron-absorbing materials? I figure I'm either missing something here or GE went ahead and designed a system that they knew was not failsafe...or perhaps they are simply incompetent.

The reactor is flooded with neutron absorbing materials in emergency situations. A boric acid solution, to be specific. Doesn't change the fact that there's upwards of 10 Megawatts of heat inside the pressure vessel not caused by fission between fuel elements. The reactor was built with all of the failsafes and safety systems shared by other third-generation BWRs.

One question that I do have, which meshes with your concerns is the lack of safety rods. I would like to know why these reactors were not equipped with safety rods.

Control rods are used to control the fission. Safety rods are used to completely stop the fission in an emergency. If I were king, I would insist that all reactors have a system of independent safety rods capable to halting the fission despite any void coefficient changes.

Because the fission is completely stopped by the control rods alone. A full scram of the reactor will stop fission. If all of the rods are not raised, the boric acid injection system will start.

The remaining decay heat comes from fission processes within the fuel elements themselves, and is impossible to just stop. You can prevent the elements from interacting with each other, but the rest is all internal.

[razark]

Originally Posted by Skybird

... they just copied design plan by General Electric without thinking a second thought about it.

I find the lack of considering ANY situation requiring an emergency insertion of control rods a mind-blowingly stupid oversight.

Edit: I am referring to everyone involved in the design, both the original designers, and those that copied it.

Originally Posted by ASWnut101

Second, BWRs have a steam dryer directly above the reactor core. This is the primary reason why the control rods are inserted from the bottom, as there's a bunch of crap blocking insertion from above. It would also have the effect of blocking any safety material dropped from the top.

Ah. That explains that part.

[krashkart]

Originally Posted by Biggles

While the world concentrates on the nuclear disaster, victims of the tsunami and the earthquake elsewhere are having major problems with the winter. Several elderly civilians have died from the cold, according to Swedish newspapers.

This picture breaks my heart, every time I see it...

If Fukushima Dai-ichi were a coal- or gas-fired plant nobody would care about it. But since it's a nuclear power plant, the imaginable possibilities overshadow the human tragedy that's already in place.

[papa_smurf]

Latest from BBC news:
Cable reaches Japan nuclear plant

Engineers at Japan's stricken Fukushima nuclear power plant have successfully connected a power line to reactor 2, the UN's nuclear watchdog reports.
Restoring power should enable engineers to restart the pumps which send coolant over the reactor.

[RickC Sniper]

Originally Posted by Skybird

German Die Welt reports that the two chief designers of the reactor admitted that nobody took into account the possibility of earthquakes beyond 8.0 or tsunamis, and that instead they just copied design plans by General Electric without thinking a second thought about it.

http://www.welt.de/vermischtes/artic...spanne-zu.html

I don't have the source handy, but I recall reading that these plants were designed to withstand an 8.2 earthquake, and this earthquake was SEVEN times more powerful than an 8.2.

The reactors withstood the earthquake just fine. It was the tsunami wiping out their power that caused this mess.

[papa_smurf]

Originally Posted by RickC Sniper

I don't have the source handy, but I recall reading that these plants were designed to withstand an 8.2 earthquake, and this earthquake was SEVEN times more powerful than an 8.2.

The reactors withstood the earthquake just fine. It was the tsunami wiping out their power that caused this mess.

Think it was re-classified as a magnitude 9.0 once all data had been collected.

[RickC Sniper]

Why are you guys going on about the control rods and their design?

The control rods moved into place automatically when the quake was felt, and that shut down the plants. Residual heat was the problem they could not deal with when they lost cooling ability.

[Takeda Shingen]

Originally Posted by Type941

on thing i gotta say - looking at how japanese people handle themselves in light of this disaster (the dignity, no looting, no robbing, crime hikes, agression, etc) - it's extremely admirable and gives hope humanity has a chance. Because really all are animals deep down and fact that they have so much bravery and dignity in face of this it's unreal.

Just comparing this to the looted car dealerships in Egypt or looting of Iraq Museum or Katrina looting in New Orleans... we're may be not all the same underneath after all.

Absolutely. Could you imagine if this had happened stateside? Talk about total societal breakdown.

[Oberon]

Originally Posted by krashkart

If Fukushima Dai-ichi were a coal- or gas-fired plant nobody would care about it. But since it's a nuclear power plant, the imaginable possibilities overshadow the human tragedy that's already in place.

This... *sigh* So very much this...

[Reece]

Originally Posted by krashkart

If Fukushima Dai-ichi were a coal- or gas-fired plant nobody would care about it. But since it's a nuclear power plant, the imaginable possibilities overshadow the human tragedy that's already in place.

I quite agree mate, The guy in the picture probably lost his wife and family, house, everything, not much to live for, and that is only one example!

[Gargamel]

Not sure if this is legit or not, as the source is a comedy web-lolz site, but it wouldn't really surprise me if the Japanese were really this effecient.