# Nuclear physics anyone?



## diddi (Mar 20, 2011)

Can anyone shed some light on a bit of a grey area for me... 

The terrible events in Japan have prompted me to ponder: if there is a 'meltdown' in a reactor core, which presumably means that all the fuel accumulates at the bottom of the vessle before burning its way through, why does the fuel not exceed its critical mass and a undergo nuclear fission explosion?


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## Norie (Mar 20, 2011)

No expert but I think it's something to do with how 'enriched' the uranium is.


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## shg (Mar 21, 2011)

It doesn't have the density to reach critical mass. It's physically impossible for a reactor core to explode, ever, ever, ever.


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## Sandeep Warrier (Mar 21, 2011)

I think that the meltdown is precisely the reason why there is no nuclear explosion. The amount of Uranium/Plutonium used in the nuclear fuel cells is quite small (also called enrichment).

Because of low U/Pu enrichment, the fuel cells do not undergo an uncontrolled chain reaction that leads to a nuclear explosion.


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## Atroxell (Mar 21, 2011)

Also not a physicist, but...

After the accident, I did a LOT of surfing in an attempt to find out what was going on and what might happen.

It appears that, although any nuclear accident is not something to be taken lightly, this type of reactor can never truly have a "meltdown". A meltdown is where the fuel actually melts and cooks its way through the containment vessel. Even the Chernobyl "meltdown" only made it to the sub-floors of the building before stopping the burn. The reason why that happened was because there was not containment at Chernobyl. The melt left a melted pile of nuclear material called "the elephant's foot". Google it, there's pics... The radiation from that pile was so sever that it killed several robots before they were able to get one close enough to take a picture. Somewhere around 15 or 20K rads if I remember correctly.

I don't understand the precise details, but from what I read the light water in these reactors is actually part of the medium that controls the reaction. As water levels drop in the core, the sleeves (made of zirconium oxide) holding the fuel can heat up and melt, exposing the fuel, which could possibly drop to the floor of the vessel. But the material itself, a ceramic form of uranium, which from what I have read, is incapable of the heat levels of the Chernobyl reaction. Also, with the water level drop, they supposedly cool down on their own after a few weeks...

But when you factor in an earthquake, tsunami and fire, things probably get a bit more complicated. In all likelihood, at least some of the fuel has dropped to the bottom of the containment vessel. They really won't know for some time, as there are so many variables that have to be considered and eliminated before they can even go in to take a look.

Further, if these reactors should somehow find a way to "meltdown", their design is such that the fuel would burn through containment into a specially designed cavity under the reactor vessel that disperses the fuel to the point where the reactivity would diminish to the point of making it a "cleanup job". 

Luckily for everyone, they don't appear to be heading that way...

But again, I am not a physicist and there's always the chance that I have misunderstood or misinterpreted something, so there's my two cents...If there are any physicists out there, love to hear from a pro.


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## diddi (Mar 21, 2011)

sandeep.warrier said:


> The amount of Uranium/Plutonium used in the nuclear fuel cells is quite small



thats what i thought too, BUT last night on a reputable current affairs program a UK expert indicated that reactor 4 contains *98 Tonnes *of uranium. the hiroshima bomb contained 60kg of uranium which in physical size is about a 15cm (6") cube.

also it was stated that one of the reactors was running on plutonium, not uranium, which from my understanding is even more active than uranium.

the expert observed that should the reactor 'meltdown' then there would be an explosion, but that it would be due to overheating and the result would produce the equivanent of what is termed a 'dirty bomb' which is basically an ejection of radioactive waste which causes contamination rather than a fission chain reaction.  and that brings me back to my OP 

is it that the critical mass of the various isotopes is widely variable?

Luckily, as has been noted, it seems that the worst has passed.


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## shg (Mar 21, 2011)

The enrichment for uranium as fuel is much less than enrichment for weapons. The plutonium is a byproduct of the fission reaction, which is why it appears in spent fuel. The ability to extract it in reprocessing is why non-nuclear countries are 'encouraged' not to do their own reprocessing. 

At high temperatures (think uncovered fuel rods sprayed with water), the zirconium reduces the water, producing zirconium dioxide and hydrogen gas. The hydrogen looks for any excuse to explode.


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## diddi (Mar 21, 2011)

OK, so heres my latest take on the subject.

it seems that reactor grade uranium is about 5% U-235 which is the highly reactive bit and the rest is U-238 which actually slows the chain reaction effect exhibited by the U-235.

U-238 does not support chain reaction decay because it absorbs neutrons, but does not re-emit them (ie the product of the reaction is a single atom) whereas U-235 fissions into Kr and Ba and releases more neutrons than it absorbs which is therefore self propogating.


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## chuckchuckit (Mar 25, 2011)

In my opinion (not a nuclear guru) the real problem all along has been, if there is a serious breach all personel would have to be totally evacuated from the plant. There would be no one to cool down "the other reactors" and many if not all six reactors could each overheat and breach their containment also.

Was watching for this early on, glad they have "perhaps" cooled enough now so there may not be such an event. Think the after effects are still going to be worse than most think. Too bad they don't error on the side of caution, instead of continually moving out the evacuation perimiters and trying to down play it, or avoid initial panic.

Chernobal had to use robot bulldozers to finish the job burying the core area due to no containment. And heard that even today the radiation levels around those still quarantined robot bulldozers is extremely high.


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## chuckchuckit (Mar 25, 2011)

Zirconia Oxide trivia...

Many moons ago (back in the 1970's) I worked for a small company that made at that time, the best oxygen analyzer in the world. It was based upon a Zirconia Oxide ceramic tube that was heated to 750 degrees centegrade. Had platinum electrodes pasted to inside and outside of the tube. The outside of the tube had stable room air, and inside the tube we would flow an inert (non-explosive) gas that had the unknown amount of oxygen. This would create an exact voltage differental instantly which represented the differental oxygen concentration in the gas inside the tube compared to the outside of the tube air. Extremely fast, and extremely accurate. Provided you kept the temperature stable on the hot end of the Zirconia tube. And kept the temperature of the analog calculating circuitry stable too, as we were pushing the electronics of analog circuits to their max back then to get the high precision measurments we were getting.

The Zirconia Oxide ceramic tube was a little bit bigger than a person's finger. Extremely strong for a ceramic as we would have to cut them with diamond saws using water to keep the saw cool.

But once heated to 750 degrees centegrade, if we wanted to work on the Zirconia tube for any reason, we had to let it slowly cool for a couple days in its containment housing, or it would immediatly crack if exposed to room air anywhere near the heated end.

I have a hard time imagining pouring water on those reactor Zirconia tubes filled with hot uranium etc does not crack them. Especially once they are exposed to air and thus the zirconia surface temperature is raised with huge temperature gradients through them. Our Zirconia tubes had huge temperature gradients also from the hot 750 degree celsius tip, to the other end closer to room temperature. But this was not a problem as long as the "temperature changes were not made quickly". Otherwise they would crack open every time.

I would think most all those reactor Zirconia tubes are cracked that were exposed and then had much colder water directly sprayed on them in those cooling ponds. And maybe also inside the reactor itself if they were exposed and then cooled too quickly. Their leaking radiation remaining inside containment hopefully. It has got to be quite a mess in all those reactors by now as I am sure all of them had exposed hot zirconia at one time or an other, that they desperatly tried to cool down with water cracking or even shattering their Zirconia enclosures.

Been a while since I have thought about Zirconia, but this brought back a lot of old memories.


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## diddi (Mar 25, 2011)

So what you're saying is that we are probably not hearing a very true assessment of the likely degree of damage and lack of containment of radioactive material. No wonder their foods and water are being affected as is being reported...


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## chuckchuckit (Mar 25, 2011)

I think it is much worse than they are saying which we will find out more about as time goes on.

But worse than that is the potential for escallation of radiation is far beyond what most people even suspect. I think they are just gambling that it will not get out of control. Enough time has past to where maybe it won't from here on, but I think it was way more dangerous there in the beginning than was ever even hinted to.

They may have been afraid of starting a mass panic (39 million people in the Tokyo area), but I think that is not the main reason for such down playing. It is rather a sweeping under the rug approach and even corruption without concern for the possible consequences that has always happened with their nuclear facilities.

They may have averted a massive tragedy with this nuclear facility, but doubt they are fully out of the woods yet. Many people there are undoubtably sacraficing their lives (literally) to try and avoid the worst case. If it weren't for them I think there for sure would have been a massive tragedy perhaps beyond the effects from the earthqauke and Tsunami combined.


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## B0Z0 (Mar 26, 2011)

diddi said:


> Can anyone shed some light on a bit of a grey area for me...
> 
> The terrible events in Japan have prompted me to ponder: if there is a 'meltdown' in a reactor core, which presumably means that all the fuel accumulates at the bottom of the vessle before burning its way through, why does the fuel not exceed its critical mass and a undergo nuclear fission explosion?


Once again, I am just a layperson but this is my understanding of the reason why the meltdown won't cause a nuclear explosion:
In a nuclear bomb, there are three explosions. The initial catalyst is a chemical explosion around the plutonium that compresses the plutonium to a point that starts the fission explosion, the fission explosion then triggers the third part of the bomb which a fusion fuel and this third explosion is what gives the bomb its power as it uses the surrounding environment as its fuel ie fusing two hydrogen atoms into helium and releasing excess energy.

In a meltdown there is no catalyst to make the plutonium start the fission process (plus the plutonium is not as enriched as in a nuclear weapon) and if there was then there would have to be a fusion fuel that requires the fission process as its catalyst for the meltdown to resemble a nuclear explosion. 

The problem with a meltdown is the invisible-to-the-eye radioactive material that can escape into the environment if it is not contained. There won't be a destructive force emanating from ground zero but there will be unstable atoms released into the air that can affect those atoms around it until it has enough half lives to become stable.


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## diddi (Mar 27, 2011)

the typical U-235 or Pu-239 bomb does not require hydrogen to be self sustaining. for plutonium, even a weakly enriched sample with say, 15% Pu-239 has a critical mass well under 20kg.  this corresponds to a cube less the 10cm wide.

in certain fission bomb designs a small H-fusion reaction is the SECOND stage of triggering, not the third.  this increases the initial bombardment of neutrons on the fissionable fuel to reduce wastage.


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## diddi (Mar 28, 2011)

i hear in todays news, evidence of major containment problems in Japan, with the discovery of plutonium outside the reactor along with highly deuterated water puddles. makes one wonder what the true extent of the problem is...


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## Expiry (Mar 30, 2011)

I know nothing about Nuclear power, which will become apparant with this question, I'm sure.

Is radiation a byproduct of nuclear power, or is it the radiation that produces the energy?

Basically, what I'm asking is, why can't we use ALL of the power (radiation) that is created which would therefore mean there's no such thing as nuclear waste?

I have a feeling this is a stupid question.


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## diddi (Mar 30, 2011)

the uranium in the nuclear fuel is a mixture of 2 different types.  one is U-235, and the other U-238.  if you have been following the thread, you will have noted that both are discussed.  U-235 is the highly reactive part of the fuel and is responsible for all of the nuclear energy production.

in a normal reactor there might be about 4% U-235; all the rest, at least initially, is U-238. enery is produced when the U-235 atoms split into parts. a large atom of uramium can break up into 2 smaller atoms...

eg  uranium-235 -> barium + krypton + lots of energy (as radiation)

this reaction is caused by smashing the U-235 with a neutron. one of the byproducts of the reaction is more neutrons, which flood into the fuel and cause the reaction to continue without re-triggering.

many of the neutrons don't hit another atom of U-235 since there is anly a small percentage present. the rest is U-238. when U-238 is hit by a nuetron, the neutron is absorbed and so U-239 is produced, but nothing else. this slowly turns into plutonium over a period of weeks.

so to answer your question...  after a period of years, there are the following materials in the reactor:

U-235  (still to be used)
U-238  (still to be used)
U-239, Np-239 (intermediate steps towards plutonium)
Pu-239 (material identical to that used in Nagasaki bomb 1945)
Ba, Kr, Cs, Rb, I, etc  (all radioactive products from U-235 splits)

there is a huge amount of left over material, virtually all of which is radioactive (ie it can undergo another nuclear reaction), and that is what the anti nuclear proponents complain about.  also, every country with nuclear reactors for electricity generation is breeding plutonium as a by-product which can used in nuclear weapons.


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## chuckchuckit (Mar 31, 2011)

It sounds like any one of those materials from a reactor could do serious harm (as we are starting to see with the reactors in Japan).

The unfolding accident in Japan is a serious concern worldwide. Water, soil, food chain contamination etc. It is unfortunate most people do not see the true danger of these materials getting into the hands of terrorists, and what they will do with it.

Not to mention the enriching of plutonium by terrorist supporters. Perhaps the Japan accident will give a reason to not keep overlooking this event that some say is just a matter of time. At some point it will be too late.

"Why" this does not concern people "before it is too late", is a valid question...


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## diddi (Mar 31, 2011)

yes, it now appears that in Japan the exclusion radius is to be expanded and that the sea water is becoming considerably more contaminated.

the notion of terrorist access to fissile material is quite real. that is why there is so much concern about 'rogue nations' with terrorist sympathetic tendencies having ANY forms of nuclear development because the ever peaceful nuclear power plant is also a plutonium breeder, and whilst Pu bombs are more difficult to make over U-235, 'where there's a will...' to coin a cliche.


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## chuckchuckit (Apr 1, 2011)

And terrorists have proven many times that they like to wait until they can “set them all off at once” for maximum effect. Perhaps 19 will be their goal?
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Even if only one dirty radiation bomb or plutonium device is detonated in a city or port (hidden in an incoming ship), it would start a mass panic of living and dying “contaminated people and vehicles” spreading radiation as they flee in all directions. Detecting more hidden nuclear bombs or radiation devices not detonated yet in other cities might be difficult as radiation would already be spread everywhere.
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Perhaps people are not concerned enough to actually do something about stopping this real threat that would likely destroy civilization as we know it, because it does not seem real (yet). Instead of a person “taking the time” to think things through for themselves, it is easier to just let “the media experts” tell us.
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I would say that our decades and generations of “media entertainment absorption” have blurred the lines between fantasy and reality. Hollywood can even turn nuking one of our cities into “entertainment”. If “everything” becomes entertainment, we can lose the capacity to know the difference between reality and fantasy, and truth or lies. Including losing the capacity to be able to fear true danger, when it is right before us. Because it all seems like entertainment. If we do not like what is entertaining us, we just change the channel.
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Very slowly it has taken decades and generations to get to this point. We are headed for big trouble, and it seems we may have lost the capacity to even know it. “Instead” of looking the other way and pretending it is not real, it will instead take courage, and speaking out about it. Perhaps even the “combined courage” of the people of many nations. And then actually do something about it, by literally putting a stop to it. Before one day very soon, it will “most certainly” be too late.


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## Dryver14 (Apr 9, 2011)

Stop it chuck,

you will have me walking arund in a lead lined suit!.

I am sure people are trying to stop terrorists obtaining any kind of nuclear material, one thing I am sure of is that if they do they wll not wait until they have 19. 1 will do, the dilema will be do they hit NewYork, Washington, Israel or London.

The power stations are going nowhere though and with real expectations of oil running out in the next 20 years even anti power station people will convert once the lights go off and more will be built, Ive not read into this power source but are they just big steam generators?


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## diddi (Apr 9, 2011)

yeh, the nuclear fuel generates heat which in turn is used to produce steam. same principle as coal or gas but different fuel source. each one has the same basic flaw, and that is they all produce byproducts which are undesirable, so we are forced to elect which we believe is the lesser of 2 evils, CO2 or radioactive waste.  or we can all work smarter on sustainable 'green' power sources and make more efficient use of what we have.


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## chuckchuckit (Apr 10, 2011)

For some, it may require finding their courage to even be able to think things through.
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Iraq was developing nuclear weapons and Israel stopped them by bombing the Iraq nuclear facility in 1981 (see Link 1).
<o></o>
The Iraq nuclear weapons program had to be stopped again more than 10 years later, during the Bush administration by the USA and other countries during the Gulf War (see Link 2).
<o></o>
Libya was developing nuclear weapons and was stopped during the Bush administration. Libya turned over their Nuclear Weapons developments around the same time the war in Iraq began (see Link 3).
<o></o>
Iran currently “is” developing nuclear weapons and no one is stopping them.
<o></o>
“When” Iran has nuclear weapons the suicide bombing terrorists will have nuclear weapons. “When” they detonate the first one in a major city, then “everyone” will want to stop them.
<o></o>
It then will become “everyone’s” most important concern. More important than the economy. More important than the environment. Even more important than the latest Hollywood movie. Almost everyone at that time will try to find their courage. But it will be too late.
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“Now” is the time to find the courage. Not then. Because “then” it will be too late.
<o></o>
Link 1: http://en.wikipedia.org/wiki/Osirak_Nuclear_Reactor
<o></o>
Link 2: http://www.fas.org/nuke/guide/iraq/nuke/program.htm
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Link 3: http://articles.cnn.com/2003-12-19/world/libya.nuclear_1_british-inspectors-nuclear-program-libya?_s=PM:WORLD
<o></o>
<o></o>


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## Dryver14 (Apr 11, 2011)

chuck,

I sort of agree with you but i still stick with the point that as long as the lights are on people wll lean towards "a blind eye" as far as this power source is concerned.

Had we put as much money into alternative power which will be needed to save lives as we had to save banks we could probably solve the issue.


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## diddi (Apr 12, 2011)

Another earthquake, and the disaster level is raised to 'Critical'. yet there is precious little about what is happening. i know it could cause panic, but surely every deserves to be informed.


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## WaterGypsy (Apr 12, 2011)

Dryver14 said:


> chuck,
> Had we put as much money into alternative power which will be needed to save lives as we had to save banks we could probably solve the issue.


 
While I'd like to think we could solve all our problems with alternative energy sources I realise that is pretty much a pipe dream .... I found this link a little while ago and it makes interesting reading - its a pity the politicians can't / won't think as clearly about the subject

http://www.withouthotair.com/


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## Dryver14 (Apr 12, 2011)

Thats a good read WaterGypsy,

I get that my statement about the problem being solved was maybe a little rash but not entirely without cause as in, the level of the ability to relsolve anything is often driven by the motivation to resolve it in the first place. Economics drive everything at the moment but i envisage a change,

I have often used the comment..

"what?, you mean I can have better summers in the future and all I have to do is sacrifice Norfolk".

When Nations put their minds to do something it generally gets done, take the space race for example.

I'm rambling now..... I refer the honorable gentleman to my earlier answer,

People will not care what the power source is as long as the lights stay on.


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## WaterGypsy (Apr 12, 2011)

Dryver14 said:


> Thats a good read WaterGypsy,
> "what?, you mean I can have better summers in the future and all I have to do is sacrifice Norfolk".


 
ROFLMAO ..... sorry Norfolk I do like you really


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## diddi (Apr 12, 2011)

that looks like an interesting read.  i'll have a better look when i have a few spare hours.


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## chuckchuckit (Apr 21, 2011)

Green Power’s Latest Advocate
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He still works for the same boss he has always worked for.
<o></o>
Why would he and his boss be so excited about getting everyone involved in Green Power?
<o></o>
The big diversion…?
<o></o>
http://www.foxnews.com/us/2011/04/19/charles-manson-reportedly-breaks-20-year-silence-talk-global-warming/
<o></o>
*Charles Manson Reportedly Breaks 20-Year Silence to Talk About Global Warming<o></o>*
Published April 19, 2011<o></o>
FoxNews.com<o></o>
Charles Manson broke a 20-year silence on the 40th anniversary of his conviction in the murders of eight people, including actress Sharon Tate, to speak out about the so-called perils of global warming, the U.K. Daily Mail reports. <o></o>
The 76-year-old cult leader, who in 1969 led his followers to murder eight people, spoke about the "bad things" being done to the environment in an interview Monday with Vanity Fair Spain magazine. <o></o>
"Everyone's God and if we don’t wake up to that there’s going to be no weather because our polar caps are melting because we’re doing bad things to the atmosphere," Manson reportedly said in a rambling jail cell interview from California’s Corcoran State Prison. <o></o>
"If we don’t change that as rapidly as I’m speaking to you now, if we don’t put the green back on the planet and put the trees back that we’ve butchered, if we don’t go to war against the problem..." he reportedly said. <o></o>
Manson also described himself in the interview as a "mean guy" and an "outlaw," according to the Daily Mail.<o></o>
"I'm everything bad," he reportedly said.<o></o>
Manson led the group known as the Manson Family, which in 1969 murdered eight people, including film director Roman Polanski's pregnant wife Sharon Tate. He is serving a life sentence for his role as the convicted ringleader in the gruesome murders.<o></o>
<o>*Click for more on the Charles Manson interview from the U.K. Daily Mail* 
</o>


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## chuckchuckit (May 3, 2011)

The below article is why terrorists cannot be allowed to have any nukes. No matter what it takes to stop them. The terrorists in that article are telling us straight out that they are going to nuke us as soon as they can. Even claiming now that they have a nuke hidden in a city they are going to detonate. Their goal can’t be any clearer than that.
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Those who think developing green power is more important than stopping Iran from developing nuclear weapons power, is helping the terrorists. Nothing would please Manson’s boss more than “diverting our attention away from terrorists getting nukes”. Manson’s boss (as he has tried before) will then proceed with his ultimate goal to destroy the human race. And we are allowing it. Because it is easier to feel good about going green, instead of finding the courage to stop the terrorists. Manson’s boss has always tricked people through their feelings and emotions. That’s how he does it.
<o></o>
See the “1938 Munich Agreement” sometimes also known as “Peace for our time” which is where Hitler signed the paper desiring peace. Hitler then made fools out of them all when soon after that he invaded Poland starting WWII. (See below Link 1 and Link 2).
<o></o>
The pacifists convinced everyone to look the other way while Hitler built his weapons. Then 60+ million people died in WWII. This time pacifism will likely get a billion or more killed when terrorists get nukes.
<o></o>
Iran has to be stopped from getting nuclear weapons. The cost now to do so is nothing compared to what it will cost if we don’t. According to the article below, it may closer to “too late” than we think. The article below is extremely clear.
<o></o>
http://www.foxnews.com/world/2011/05/02/11-mastermind-warns-nuclear-hellstorm-bin-laden-killed/
<o></o>
*9/11 Mastermind Reportedly Warned of 'Nuclear Hellstorm' if Bin Laden Killed<o></o>*
Published May 02, 2011<o></o>
| FoxNews.com
The self-proclaimed mastermind of the 9/1l terror plot told interrogators at Guantanamo Bay that Al Qaeda has a nuclear bomb somewhere in Europe and would detonate it if Usama bin Laden was ever captured or killed, The Daily Telegraph reported, citing WikiLeaks’ cables.<o></o>
Khalid Sheikh Mohamed, one of the top prisoners at the facility, called the plan a “nuclear hellstorm.” The report, which was first published late last month, said some detainees had comprehensive knowledge of Western countries’ nuclear defense.<o></o>
There was no immediate indication that bin Laden's killing last weekend by the U.S. would prompt Al Qaeda to carry out such a threat, or if it even has the capabilities.<o></o>
To be sure, cables show U.S. authorities uncovered a number of attempts by Al Qaeda to obtain nuclear materials, according to the report.<o></o>
The WikiLeaks cables about Guantanamo, obtained and detailed last month by several news organizations, illustrated how intelligence agencies employ information obtained by the 780 prisoners. Although some of the information is proved to be erroneous, still some appears to be actionable.<o></o>
Separately, a prisoner described as the 20th 9/11 hijacker said the terror group is seeking to recruit staff at Heathrow Airport in London and plotted major chemical and biological attacks against the U.S. 
<o></o>
Link 1: http://en.wikipedia.org/wiki/Peace_for_our_time
<o></o>
Link 2: http://en.wikipedia.org/wiki/Munich_Agreement


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## Joe4 (May 3, 2011)

We are wading dangerously close into the political realm here, which we do not allow (see this sticky here: http://www.mrexcel.com/forum/showthread.php?t=512003).

We ask that we keep politics out of it, or this thread/replies will need to be removed.


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