Major Earthquake & Tsunami in Japan

[G.T.Ace]

That's not an extent threat, merely a putative one. And since "another Chernobyl" is fundamentally impossible in a non RBMK reactor, quite an imaginative, putative one at that.

The chemicals from the Ichihara fire are already up there, already causing damage. The radiation levels detected in inhabited areas as a result of Fukushima I are not medically significant.

It's still a threat and yes another "Chernobyl" is unlikely, but it could be worse than Chernobyl on a level we cannot even imagine, it could be less dangerous too, no one can predict that. Not saying the Ichihara fire is good, but it's just a really small danger compared to what could happen in Fukushima, not even close.

EDIT:
And yes, I know all the stuff with the graphite, which caused the radiation to travel that far, but even half the area from back then would be worse than Chernobyl. The radiation only needs to spread 300 km and it would be a complete disaster.

 

[ironcobra]

The chernobyl disaster was caused when an explosion tore open the reactor vessel and exposed the fuel and it's GRAPHITE (huge difference between this and the japanese reactors here) moderator were exposed to air allowing them to burn openly and disperse huge amounts of material into the air. Even IF the reactor vessel of reactor 2 is damaged enough to expose the fuel the lack of catastrophic damage and burning graphite means that there is NO comparison to chernobyl. What is possible right now is a full meltdown which could contaminate the surrounding ground and possibly even oceans for a long time to come.

I still believe Nuclear is a safe efficient method for energy production and I wish those that are blindly saying no nuclear would get their facts straight before blindly following the rest of the crowd.

I thought they said the rods were exposed at times during the first few days and there have been numerous explosions are you aware what happens when the rods fuse together and incase the inner rods? They have already dumped sea water in there which makes hydrogen(explosive)? You guys are undereducated on power if you think nuclear is the best power source we have, no containment blah we build con contain that kind of power!! We have geothermal hotspots everywhere on this planet that will provide infinite power to us, natures nuclear power remember, is it iceland that uses this?? How about solar farms? How about Tidal Power/Energy? Its propaganda like this from nuclear and oil companies claiming there is no threat from there programs(Japan,Gulf of Mexico?) that keep these clean sources of limitless power from being used. We will not make it much further as a human race until we realize mother nature has provided us with an unlimited amount of power dont you think??

 

[Famine]

ironcobra - there have been no explosions involving fissile material nor primary containment at Fukushima I. The explosions you have seen have been caused by seawater used for cooling heating up and forming hydrogen gas - which is then ignited. The buildings which were damaged are not for protecting the outside world from the reactors, but protecting the reactors from the outside world - weatherproofing.

That's not to say no radiation has leaked or that no meltdowns have occurred (incidentally "meltdown" does exactly what it says on the tin - it melts down. Not "explodeup"), but that the explosions you have seen were not radiologically important.

It's still a threat and yes another "Chernobyl" is unlikely

No, the key word is "impossible". What occurred at Chernobyl cannot occur at Fukushima.

As above, that's not to say that there won't be a significant release of radiation of some variety at some point - what occurred at Three Mile Island might occur here - but that a Chernobyl-type accident is not possible.


The carcinogens released by the Ichihara fire are, on the other hand, real and present. And carcinogenic.

 

[G.T.Ace]

Let me rephrase this: What happend at Chernobyl cannot happen there, but the effects it could have could be (could could could....) worse than what happend in 1986. Actually, there were already accidents (at least one) which were already worse, but just haven't really affected more poeple so far.

Like I said, the radiation only needs to travel 200-300 km and would hurt more people than the Chernobyl accident.

 

[ironcobra]

ironcobra - there have been no explosions involving fissile material nor primary containment at Fukushima I. The explosions you have seen have been caused by seawater used for cooling heating up and forming hydrogen gas - which is then ignited. The buildings which were damaged are not for protecting the outside world from the reactors, but protecting the reactors from the outside world - weatherproofing.

That's not to say no radiation has leaked or that no meltdowns have occurred (incidentally "meltdown" does exactly what it says on the tin - it melts down. Not "explodeup"), but that the explosions you have seen were not radiologically important.



No, the key word is "impossible". What occurred at Chernobyl cannot occur at Fukushima.

As above, that's not to say that there won't be a significant release of radiation of some variety at some point - what occurred at Three Mile Island might occur here - but that a Chernobyl-type accident is not possible.


The carcinogens released by the Ichihara fire are, on the other hand, real and present. And carcinogenic.

I am very aware of that, those explosions help to break contamination tho? and when these rods meltdown into the ground whats to keep it out of the ground water? Wont that then be absorbed by land/air? why are they reading dangerous levels in tokyo at times and then not, is the wind carrying it? I think so, i really believe the govt is not telling the real story here check that vid link i posted, there playing cartoons on tv and not the news. There hasnt been a meltdown yet at this type of reactor i agree but its the first time this type has been damaged right? So how do they or u know 100% there is no fallout from this type of reactor? There is obvisouly a leak to atomsphere already or there wouldnt be radiation detected 200km away in tokyo 200km!!! that is pretty serious already if it hasnt even melted down yet which is certain, because they can no longer get close hence dumping water on nuclear reactors from helicopters lol. funny but not very funny

 

[land sea air]

I thought they said the rods were exposed at times during the first few days and there have been numerous explosions are you aware what happens when the rods fuse together and incase the inner rods? They have already dumped sea water in there which makes hydrogen(explosive)? You guys are undereducated on power if you think nuclear is the best power source we have, no containment blah we build con contain that kind of power!! We have geothermal hotspots everywhere on this planet that will provide infinite power to us, natures nuclear power remember, is it iceland that uses this?? How about solar farms? How about Tidal Power/Energy? Its propaganda like this from nuclear and oil companies claiming there is no threat from there programs(Japan,Gulf of Mexico?) that keep these clean sources of limitless power from being used. We will not make it much further as a human race until we realize mother nature has provided us with an unlimited amount of power dont you think??

the rods were exposed to air within the core which is dangerous, but a very different situation than chernobyl.

I don't remember any propaganda in this thread, just facts about what has happened in japan vs what happened in Chernobyl.

Again, research this stuff a little bit before you come in here repeating a bunch of fear mongering nonsense.

 

[Dotini]

As above, that's not to say that there won't be a significant release of radiation of some variety at some point - what occurred at Three Mile Island might occur here - but that a Chernobyl-type accident is not possible.

Was there in fact any significant release of radiation at TMI?

 

[Famine]

Let me rephrase this: What happend at Chernobyl cannot happen there, but the effects it could have could be (could could could....) worse than what happend in 1986. Actually, there were already accidents (at least one) which were already worse, but just haven't really affected more poeple so far.

Like I said, the radiation only needs to travel 200-300 km and would hurt more people than the Chernobyl accident.

Just for reference, the peak radiation level recorded in Tokyo thus far is 0.9uSv/hr. If this level persists, the average resident of Tokyo will receive the same annual dose of radiation as a member of transatlantic flight crew - and it's one-twelfth the level considered medically relevant.

I am very aware of that, those explosions help to break contamination tho?

No.

and when these rods meltdown into the ground whats to keep it out of the ground water?

They don't melt down into the ground. They melt down onto a giant, massively thick concrete floor - if the melt breaches second containment, that is (considering second containment is a thick metal shell with a melting point of 2,200 degrees.

why are they reading dangerous levels in tokyo at times

They aren't. See the response I just gave to G.T.Ace.

There hasnt been a meltdown yet at this type of reactor i agree but its the first time this type has been damaged right? So how do they or u know 100% there is no fallout from this type of reactor?

Fallout? Nobody's set off a nuclear bomb you know - and reactors aren't bombs. When they have a runaway reaction, they melt. They don't explode and shower radiation everywhere. Nuclear bombs are quite hard to make, in fact.

There is obvisouly a leak to atomsphere already or there wouldnt be radiation detected 200km away in tokyo 200km!!!

That's probably due to the fire at the spent fuel store.

that is pretty serious already if it hasnt even melted down yet which is certain

It's certain?

 

[Griffith500]

The water bombing has apparently proved quite effective.

The Hydrogen can be formed easily without seawater - see thermal dissociation. In fact, during normal operation, Hydrogen is actively pumped into the reactor!

The problem was when the hydrogen mixed with oxygen in explosive proportions (see explosivity limits), which first happened outside the hermetically-sealed, nitrogen-flooded containment area. One explosion occurred in / near the suppression pool (which, under normal operation, uses electricity to scrub excess hydrogen from the vapour phase down into water again) which may have damaged it (reactor No. 2) - this is not part of the containment structure.

The hydrogen generated in the spent fuel pool at No.4 mixed with air (oxygen) immediately, and so posed a fire and / or explosion threat almost immediately.

 

[ironcobra]

the rods were exposed to air within the core which is dangerous, but a very different situation than chernobyl.

I don't remember any propaganda in this thread, just facts about what has happened in japan vs what happened in Chernobyl.

Again, research this stuff a little bit before you come in here repeating a bunch of fear mongering nonsense.

not sayin propaganda in this thread saying its out there right now saying these nuclear and fossil fuels are our only sources of power, they clearly are not and they should be stopped immediately we dont understand nuclear science enough to run it cleanly, if we are to avoid further destruction of our planet. Are u aware how much lobbying the nuclear/oil industry does with 100% support from our politicians and news. They will say anything to keep there precious money makers, and to say there will be no big impact to the whole nation of japan from this is irresponsible in my eyes there is 3000x times the amount of nuclear material at this plant then Chernobyl. Answer me this why is it leaking into Tokyo already if this isn't the airborne type of radiation? Do u know how many people live in Tokyo? Catastrophic already if u ask me, its just the news/gov isn't telling u yet

fear mongering...please this is a nuclear meltdown im not doing the fearmongering this is a real concern globally and to suggest otherwise is irresponsible..imo. Would u book a flight to Tokyo right now?

 

[HKS racer]

Its propaganda like this from nuclear and oil companies claiming there is no threat from there programs(Japan,Gulf of Mexico?) that keep these clean sources of limitless power from being used.

not sayin propaganda in this thread saying its out there right now saying these nuclear and fossil fuels are our only sources of power, they clearly are not

100% correct.

 

[Griffith500]

You know, technically, we don't understand biochemistry well enough to run our water treatment plants cleanly. Maybe they should all be shut down.

 

[FoolKiller]

This is a grown up conversation please go back to the playpen, this is a serious matter! and to see the irresponsible comments in this thread is disheartening, nuclear power is safe blah blah blah please

Grown-up conversation? You want to know what the only disheartening thing I see in this thread is?

A natural disaster has occurred. Thousands are dead thousands more are missing, they aren't even close to a clean-up yet and the situation at the power station is still unresolved. No one knows the full details of what is going on or what the ultimate outcome will be.

Instead of trying to find ways to help or anything some people have chosen to stand on the bodies of the dead and use this event to further their own agendas. I am appalled that politicians here in the states took to knee-jerk reactions in regard to looking at further regulating nuclear power while others have taken to using this to bash Obama's oil policy. It is bad enough to see men who have made careers out of being distasteful low lifes do it, but to see people on a site where I can feel a bit of a kinship with everyone do it makes me sick.

This thread was created to discuss the disaster and perhaps allow people to express their sympathies. To see that in the last 24 hours it has been turned into a debate about the safety of nuclear power is disgusting. We do have a thread discussing other forms of energy somewhere in here. Might be titled something about oil.

You have stooped to the level of a politician and followed the policy of "let no crisis go to waste." Fact is, as we are in a thread created for news about the disaster going on right now, in this context I do not give a frack about your opinion regarding the use of nuclear power. To bring it up in this thread is in poor taste and it does not belong. You are doing the Internet equivalent of pointing and laughing at the victims of this disaster and saying "I told you so!"

Take it to the appropriate thread, start your own thread, or just get a gorram life. I don't care. But it does not belong here.

EDIT: And while you are at it read the AUP again. Proper capitalization is expected and use of text speak, such as "u" is strictly forbidden.




Someone call the Westboro Baptist Church, I think I just found their eco-equivalent.

 

[land sea air]

Grown-up conversation? You want to know what the only disheartening thing I see in this thread is?

A natural disaster has occurred. Thousands are dead thousands more are missing, they aren't even close to a clean-up yet and the situation at the power station is still unresolved. No one knows the full details of what is going on or what the ultimate outcome will be.

Instead of trying to find ways to help or anything some people have chosen to stand on the bodies of the dead and use this event to further their own agendas. I am appalled that politicians here in the states took to knee-jerk reactions in regard to looking at further regulating nuclear power while others have taken to using this to bash Obama's oil policy. It is bad enough to see men who have made careers out of being distasteful low lifes do it, but to see people on a site where I can feel a bit of a kinship with everyone do it makes me sick.

This thread was created to discuss the disaster and perhaps allow people to express their sympathies. To see that in the last 24 hours it has been turned into a debate about the safety of nuclear power is disgusting. We do have a thread discussing other forms of energy somewhere in here. Might be titled something about oil.

You have stooped to the level of a politician and followed the policy of "let no crisis go to waste." Fact is, as we are in a thread created for news about the disaster going on right now, in this context I do not give a frack about your opinion regarding the use of nuclear power. To bring it up in this thread is in poor taste and it does not belong. You are doing the Internet equivalent of pointing and laughing at the victims of this disaster and saying "I told you so!"

Take it to the appropriate thread, start your own thread, or just get a gorram life. I don't care. But it does not belong here.



Someone call the Westboro Baptist Church, I think I just found their eco-equivalent.

Agreed, and for what it's worth sorry for my part in it.

 

[nk4e]

No form of energy production is risk-free or cost-free, and nuclear power is relatively safer than other forms of energy production. If safety were the only consideration (which it isn't), then I'd get rid of coal mining long before nuclear power. Coal mining costs thousands of lives every year, and has cost hundreds of thousands of lives over the last century - and that is just the direct cost (the number of people killed in the activity of mining coal). The resulting health and environmental costs of coal mining and usage can only be imagined, but you can be assured that these costs are significant. Oil and gas taken together would also have to go too. Even solar power is not environmentally neutral - while the energy is free, clean and abundant, the technology required to harvest it is expensive, and has numerous environmental impacts (such as those incurred harvesting the required materials to make solar panels etc.).

The fact is that we need energy to survive and there will always be some risks and costs that can only be minimised, and not eradicated altogether. Nuclear power, in that regard, is no different to any other energy source. The hazards may be different, and the costs of (rare) accidents might be (but also may not be) very high - but taken on balance, nuclear hasn't (and most likely never will) be as risky or as costly as our reliance on fossil fuels.

I wonder if the USA has supported alternative energy ways. Around L.A. I see giant fans and around Las Vegas, I have seen Solar Panels at the Edwards Air Base.

i agree but for sake of argument he said there has never been a nuclear meltdown did he not?? and ill wave my no nuclear flag whereever i want its my right in an opinion forum

I understand that you will wave your flag but like someone said. We are talking bout a tragedy and the Japanese Government ( including everyone else) are trying to stop a even like Chernobyl from happening again.

The United States of America
There have been at least six meltdowns in the history of the United States. All are widely called "partial meltdowns."
The partial meltdown at the Fermi 1 experimental fast breeder reactor required the reactor to be repaired, though it never achieved full operation afterward.
The Three Mile Island accident, referred to in the press as a "partial core melt,"[4] led to the permanent shutdown of that reactor.


This image of the SL-1 core served as a sober reminder of the damage that a nuclear excursion can cause.
The reactor at EBR-I suffered a partial meltdown during a coolant flow test on November 29, 1955.
The Sodium Reactor Experiment in Santa Susana Field Laboratory was an experimental nuclear reactor which operated from 1957 to 1964 and was the first commercial power plant in the world to experience a core meltdown in July 1959.
Stationary Low-Power Reactor Number One (SL-1) was a United States Army experimental nuclear power reactor which underwent a criticality excursion, a steam explosion, and a meltdown on January 3, 1961, killing three operators.
BORAX-I was a test reactor designed to explore criticality excursions. In the final destructive test of the reactor in 1954, a miscalculation led to the meltdown of a significant portion of the core and the release of nuclear fuel and fission products into the environment.[5]
[edit]The Soviet Union
Within the former Soviet Union, several nuclear meltdowns of differing severity have occurred.
In the most serious example, the Chernobyl disaster, design flaws and operator negligence led to a power excursion that subsequently caused a meltdown. According to a report released by the Chernobyl Forum (consisting of numerous United Nations agencies, including the International Atomic Energy Agency and the World Health Organization; the World Bank; and the Governments of Ukraine, Belarus, and Russia) the disaster killed twenty-eight people due to acute radiation syndrome,[6] could possibly result in up to four thousand fatal cancers at an unknown time in the future[7] and required the permanent evacuation of an exclusion zone around the reactor. The Chernobyl plant had containment buildings not constructed to a correct standard, allowing the concrete containment cap on the reactor to be ejected in the explosion.
[edit]Japan
Events currently unfolding as of March 16, 2011 may lead to partial or full meltdown of one or more of the reactor cores at the TEPCO Fukushima I Nuclear Power Plant.

 

[35mm]

Why? I don't think a No Nuclear avatar or flag is offensive at all.

I didn't mean literally a flag...

Still, if you want to know why, this is the reason:

To see that in the last 24 hours it has been turned into a debate about the safety of nuclear power is disgusting.

 

[Sureboss]

not sayin propaganda in this thread saying its out there right now saying these nuclear and fossil fuels are our only sources of power, they clearly are not and they should be stopped immediately we dont understand nuclear science enough to run it cleanly, if we are to avoid further destruction of our planet. Are u aware how much lobbying the nuclear/oil industry does with 100% support from our politicians and news. They will say anything to keep there precious money makers, and to say there will be no big impact to the whole nation of japan from this is irresponsible in my eyes there is 3000x times the amount of nuclear material at this plant then Chernobyl. Answer me this why is it leaking into Tokyo already if this isn't the airborne type of radiation? Do u know how many people live in Tokyo? Catastrophic already if u ask me, its just the news/gov isn't telling u yet

fear mongering...please this is a nuclear meltdown im not doing the fearmongering this is a real concern globally and to suggest otherwise is irresponsible..imo. Would u book a flight to Tokyo right now?

Firstly, type in full English please. Text talk looks horrible.

Secondly, there is NO nuclear meltdown, yet.

Thirdly, a freak event has caused this issue with nuclear power, not negligence. In fact the reality is that this event is testament to how safe nuclear power is. A massive earthquake and a very strong tsunami hitting a nuclear power plant and it hasn't completely failed?

There are always risks with energy production. Be it Nuclear, fossil, wind power, tidal power, etc. If you don't want Nuclear or any other energy production which has risks (which is all of them, in one form or another), then don't bother using any electricity, which you may find difficult.

It's a knee jerk reaction.

 

[G.T.Ace]

Just for reference, the peak radiation level recorded in Tokyo thus far is 0.9uSv/hr. If this level persists, the average resident of Tokyo will receive the same annual dose of radiation as a member of transatlantic flight crew - and it's one-twelfth the level considered medically relevant.

I know. Please don't get me wrong, I am not talking about the situation now, I just say the threat of what could happen there is huge.

I am watching Geiger counters inside of Tokyo all the time, I kinda had to laugh after they reported "high levels of radiation measured in Tokyo, 80x higher than normal" in the German TV (note, 15 or so hours after that peak they had once).

EDIT:

Hundreds of thousands of people have been evacuated from the areas worst affected by the earthquake and tsunami, with many now living in temporary shelters. The maps below show the extent of the evacuation.

http://www.bbc.co.uk/news/world-asia-pacific-12775846

 

[Dotini]

Just for reference, the peak radiation level recorded in Tokyo thus far is 0.9uSv/hr.

Elsewhere I have read the maximum cumulative radiation for a pregnant woman should not exceed 50mSv. At a rate of 0.9uSv/hr, how long would it take for the pregnant woman to receive the cumulative of 50mSv - a bit over 50,000 hours?

 

[Azuremen]

i dont need a piece of paper to know nuclear power plants are dangerous and the wrong path to energy freedom, now back to your playpen

Generally, being educated helps a profound amount in preventing you from looking ignorant. Which you have done several times now, talking about Chernobyl, explosions, and meltdown into the ground. You clearly have no idea how these systems work, nor the level of power they put out versus their general pollution levels. More so when compared to Coal power (a major source around the world) and the cost to human lives and health mining coal. Three Mile Island had a meltdown, and the radiation levels were completely trivial to the surrounding area. You are fear mongering, or so blind in your belief that you actually understand this stuff that you don't realize how out there you are.

Do you know what the bigger issue is? Japan powering itself without these reactors, not the radiation. Without power, they cannot provide services, interruptions are happening in Tokyo, and so on.

But please, make a new thread to discuss this, as it has gone far off track.

Elsewhere I have read the maximum cumulative radiation for a pregnant woman should not exceed 50mSv. At a rate of 0.9uSv/hr, how long would it take for the pregnant woman to receive the cumulative of 50mSv - a bit over 1000 hours?

1uSv = 0.001 mSv. 50/0.0009 = 55555.6 hours. Or 6.34 years.

Ninja Edit.

 

[Stevisiov]

Elsewhere I have read the maximum cumulative radiation for a pregnant woman should not exceed 50mSv. At a rate of 0.9uSv/hr, how long would it take for the pregnant woman to receive the cumulative of 50mSv - a bit over 50,000 hours?

0.9uSv/hr

Which is

21.6uSv/day

Which is

7884uSv/year

or

7.8mSv/year

So unless a pregnant mother is in pregnant for a period of 6 and a half years, then there shouldn't be an issue. And if someone is pregnant for 6.4 years, I would imagine the radiation dose is the least of their concerns.

I believe you have missed the difference between milli (m) and micro (u).

Unless I have missed something. Or my maths is more likely wrong.

[edit]Azuremen, our calculation different by a factor of two. What have I missed?

 

[Azuremen]

[edit]Azuremen, our calculation different by a factor of two. What have I missed?

Nothing much, I saw the error as well and just went through it all again. Windows Calculator did something funny when I divided by 365days/year.

My setup was 50mSv * (1000uSV/1mSv) * (1/0.9uSv/hr) * (1day/24hrs) * (1year/365day) = 6.34years

God that just looks confusing in that format Much nicer on paper.

 

[HKS racer]

I didn't mean literally a flag...

Still, if you want to know why, this is the reason:

What is disgusting? It's disgusting trying to say someone is not respecting Japanese victims because he is talking about the hazard of Nuclear. I have the maximum respect for them, and I'm concerned for their situation. Radiations (together with the oil refinery if you want) seems to be the main threats. Embassies are saying is better to leave Fukushima and Tokyo now. I can't see any logical reason why people shouldn't talk about that in this thread.

 

[Azuremen]

What is disgusting? It's disgusting trying to say someone is not respecting Japanese victims because he is talking about the hazard of Nuclear. I have the maximum respect for them, and I'm concerned for their situation. Radiations (together with the oil refinery if you want) seems to be the main threats. Embassies are saying is better to leave Fukushima and Tokyo now. I can't see any logical reason why people shouldn't talk about that in this thread.

at leaving Tokyo. Do you realize the scale of evacuating a metro area of over 30 million people? For, as the math shows, a trivial sum of radiation?

Radiations? Hazard of Nuclear? I am assuming these odd bits of grammar are from English being a second language? Read this. It translates radiation levels into eating bananas, as they are also radioactive.

The big issues here for Japan are food and shelter, and then powering their infrastructure.

 

[FoolKiller]

What is disgusting? It's disgusting trying to say someone is not respecting Japanese victims because he is talking about the hazard of Nuclear.

Turning a discussion regarding the events of a tragedy into a political soapbox is disgusting. This thread is not for debate on what kind of energy we should be using. That discussion has its place, hijacking this thread to do it is not where it belongs.

 

[G.T.Ace]

Read this. It translates radiation levels into eating bananas, as they are also radioactive.

Good that I don't like bananas.

 

[CodeRedR51]

I love bananas!

 

[ranhammerR34]

at leaving Tokyo. Do you realize the scale of evacuating a metro area of over 30 million people? For, as the math shows, a trivial sum of radiation?

Radiations? Hazard of Nuclear? I am assuming these odd bits of grammar are from English being a second language? Read this. It translates radiation levels into eating bananas, as they are also radioactive.

The big issues here for Japan are food and shelter, and then powering their infrastructure.

I wouldn't leave Tokyo for anything unless I'm heading to the South of Japan, somewhere like Kagoshima, for example. I bold highlighted the main point that Azuremen (Cody to some ) has made. That point is the most important point especially to Northeastern Japan that was rocked by the earthquake and THEN thrashed by the tsunami.

 

[Griffith500]

Good that I don't like bananas.

What's more interesting is that there is 240 times more Potassium-40 in the average person's body than there is in a banana. You pick up about 0.4 milligrammes every day (5.5 bananas' worth). Yum!

 

[Stevisiov]

Embassies are saying is better to leave Fukushima and Tokyo now. I can't see any logical reason why people shouldn't talk about that in this thread.

Embassy's are saying this as a precaution, the current threat of radiation to the inhabitants of Tokyo isn't significant currently, embassy's are probably suggesting this out of fear that the Fukishima incident significantly deteriorates.

The radiation levels would have to increase 10fold and maintain that level for a significant period of time before you should really have legitimate concerns about potential health risks. Even at those levels, an emergency evacuation of Tokyo would likely cost far more in terms human lives. Evacuating 30million people is no small operation, and that is before you factor in the danger of panic that such a move creates.