Some information about enriched uranium...

With all the talk and news about Iran and their ability to enrich uranium, I thought it might be useful to give a simplified explanation of what enriched uranium actually is, how it is used, and the differences between uranium enriched for fuel use, and uranium enriched for weapons use.

Uranium, as it occurs in nature, is made up of 3 different isotopes, each with different decay properties. Most (99.3%) natural uranium is U238, an isotope with 92 protons and 146 neutrons. Natural uranium also contains .7% U235, the isotope with 92 protons and 143 neutrons, and trace amounts of U234, the isotope with 92 protons and 142 neutrons.

For nuclear energy and weapons uses, it is the U235 that is the important isotope, because it is fissile. The U238 isotope, with its extra neutrons, tends to reflect neutrons. The U235, if hit by a single neutron, can absorb it then split, releasing energy and 2 or 3 more neutrons. These 2 or 3 neutrons will then crash into other U235 atoms, which split and release more neutrons. This chain reaction, where a single neutron produces energy and more neutrons to create more reactions, is nuclear fission.

Natural uranium, with its low concentration of U235, won't support the fission reaction. There are not enough U235 atoms for neutrons to crash into, and keep the chain going. In order to facilitate that fission chain, the concentration of the U235 isotope is increased. This is the uranium enrichment process. Enriched uranium is simply natural uranium which has been processed to increase the concentration of the U235 isotopes above the .7% concentration that it normally has. Because the U238 isotope is heavier than the U235 isotope (because of those extra neutrons), a gas centrifuge can be used to separate out the isotopes of different weights.

Now, when enriched uranium is needed to fuel a nuclear power reactor, the concentration of the U235 is increased to ~ 3.6%. For weapons grade uranium, natural uranium is highly enriched, so the concentration of U235 is 85%.

Uranium enrichment, even using gas centrifuges, is an energy and time intensive process. The equipment used to enrich NU to 3.6% for fuel use, is the same equipment that can be used to enrich it to 85% for weapons use. All that happens is that the enriched uranium is reprocessed over and over again, in a cascade of centrifuges, continually separating out the U235 from the U238. It is the same process to make nuclear fuel, it just takes a significantly more time, energy and raw materials.

Iran has confirmed they have a working 164 centrifuge cascade, and have enriched uranium. They've also announced that they've got 110 tonnes of Uranium Hexaflouride gas, the feedstock that goes into the gas centrifuges to begin the enrichment process. Iran well and truly does have the capability and the materials needed to produce weapons grade uranium, which could be used in a nuclear weapon. However, with that equipment, it will take 13 years of processing to make enough material for a single bomb.

For Iran to seriously pursue the ability to enrich uranium to weapons grade, they will need a facility or facilities with thousands of cascading centrifuges, requiring huge amounts of electrical power to run. That type of facility, or facilities, would be exceedingly hard to build, power and run in secret.

What is not being spelled out in news reports of Iranian uranium (say that 5 times fast!) is the level of enrichment and the amount of enriched material that is being produced. Those are the key questions to ask. Without those details, reports such as this one Iran Could Produce Nuclear Bomb in 16 Days, U.S. Says are meaningless, and should be shown for what they are, scaremongering hype.

Sid

This is what I've been saying for a long time now. It took the Manhattan Project 4 years to produce enough U-235 to make 2 bombs-the one tested at Alamagordo and the one used on Hiroshima. The Nagasaki bomb used Plutonium. After Aug 9, 1945 we had shot our bolt-we had no more bombs and it would have taken months to make more.

that the Little boy -gun type uranium bomb-Hiroshima bomb was not tested.

The Fat Man-Nagasaki bomb-implosion-plutonium-was tested in the U.S. and the second one used on Nagasaki.

180

Thanks.

k&r

for one bomb?

With more uranium, centrifuges and energy, more bombs could be made faster. However, there's really no way they could do that without detection.

It would be far scarier to think that they had acquired old Soviet nukes or some such, which Valerie Plame probably would've detected, before she was outed by the White House, that is.

knew how? Or can somehow more than one centrifuge speed up the process which does not seem feasible.

but building, powering and running a large centrifuge facility in secret would, in my opinion, be very difficult.

Sid

That was the State Departments estimation in the ridiculous article about the 16 days.

"Weapons-Grade Uranium

Rademaker said the technology to enrich uranium to a low level could also be used to make weapons-grade uranium, saying that it would take a little over 13 years to produce enough highly enriched uranium for a nuclear weapon with the 164 centrifuges currently in use. The process involves placing uranium hexafluoride gas in a series of rotating drums or cylinders known as centrifuges that run at high speeds to extract weapons grade uranium."
http://www.bloomberg.com/apps/news?pid=10000100&sid=aduNTcpDuDd4&refer=germany

There's a complex unit called the Separative Work Unit (SWU) that is used to do the calculation, but I didn't try to confirm the time given in the article. I'm not sure that we've got all the information needed to do the calculation ourselves.

Sid

Seems reasonable.

I agree on the power needs - they would easily be detected.

But I expect a baby nuke (perhaps even smaller than the Pakistan early tests) will be set off in the next 36 to 60 months - and more likely toward the 36 end of the range).

The decision point will come when we detect that all or most of the 54,000 centrifuges now in country are turned on, or more likely when enough have been turned on for long enough to get a small bomb. If real inspections are going on at that point we could tell if they had just developed a nuke power plant industry base, or if they were wasting the people's money on a few bombs.

I guess we can only hope for the best outcome, as we sure as hell can not change that outcome with our current defense posture.

They've got 164 on hand, and plans to build 3000 next year have been submitted to IAEA. The enrichment facility is big enough to hold 50,000 centrifuges. I think that's where the State Department pulled the number from.

Sid

:-)

Because the weights of U235 and U238 are so close, after one run through the centrifuge there is still a lot of 238 in the 235 section, and some 235 still mixed with the 238, so you need to run it them through the centrifuge again.

Later on, as the uranium gets more and more highly enriched, you have to use smaller and smaller batches in order to prevent accidentally getting a critical mass of U235 in your centrifuge.

I don't know what the critical mass is, although I expect it's easy for a chemist or physicist to calculate, but let's say it's 50kg. If natural uranium is only .7% U235, then in order to get enough U235 in one spot to use in a single bomb you need to start with 7,143kg of natural uranium, assuming the centrifuge process is 100% efficient; since it is not 100% efficient, the time and material needed is correspondingly greater.

at an unknown level of enrichment, probably closer to the 3.6% level assuming they are enriching it for fuel. It will still take years to make enough fuel to charge a reactor core with enough fuel to sustain a reaction.

straight.

180

Even the fairly small reprocessing plant Iran has now is detectable. There is significant ancillary equipment and infrastructure required to support even a small reprocessing endeavor. That's why it's not easy to hide such activities. A full scale weapons-grade reprocessing plant would be very obvious, especially if Iran attempted to bury it. The excavation alone would draw worldwide attention. The total impracticality of burying such a plant would probably eliminate that option since its location would be known by everybody regardless. We're talking about acres and acres of cascaded centrifuges here, on the order of tens of thousands of them. It's something you just cannot hide.

and people don't want to be bored with complicated facts

and Halliburton doesn't make any money from diplomacy

and the Frat Boy Messiah can't be a war preznet hero without a war

and we need to help Jesus start the end times

so all of your facts don't mean squat.

:sarcasm: (Well, actually it's probably not sarcasm. They--neocons and MSM-- actually think that way, I believe.)

If the Iranians were to use the enriched Uranium as fuel to power a reactor in order to produce Plutonium, it would also be quickly detected due to the different thermal signature between a reactor being used for power generation and one being used for Plutonium production.

Any links you can share?

:)

With a bit of help from wiki to refresh the old memory, it's been a few years since I did any of this stuff.

http://en.wikipedia.org/wiki/Enriched_uranium

Sid

The 164 vs 50,000 ? Where was that from?

This yahoo article from Tuesday:
http://news.yahoo.com/s/ap/20060411/ap_on_re_mi_ea/iran_nuclear

"Tuesday's announcement does not mean Iran is immediately capable of doing either. So far it has succeeded only in getting a series of 164 centrifuges to work in the enrichment process. Thousands of centrifuges are needed for a workable program."

snip

"Speaking before the president, Iran's nuclear chief — Vice President Gholamreza Aghazadeh — told the audience that Iran has produced 110 tons of uranium gas, the feedstock that is pumped into centrifuges for enrichment"

The "16 days article" here: http://www.bloomberg.com/apps/news?pid=10000087&sid=awSzbHpjozAo&refer=top_world_news

had this:

"``Natanz was constructed to house 50,000 centrifuges,'' Stephen Rademaker, U.S. Assistant Secretary of State for International Security and Nonproliferation, told reporters today in Moscow. ``Using those 50,000 centrifuges they could produce enough highly enriched uranium for a nuclear weapon in 16 days.''"

snip

"Iran has informed the Vienna-based International Atomic Energy Agency that it plans to construct 3,000 centrifuges at Natanz next year, Rademaker said."

Sorry 'bout the confusion.

Sid

I can only imagine the physicists spinning their heads at the M$M reporting on this. Disgusting and dangerous. :(

I know that people around here are generally skeptical of anything that the Bush administration is pushing, but thought it might be useful to give a bit of background about the topic. And as others have said on this and other threads, it would be exceptionally difficult to hide the type of facility needed for large scale enrichment efforts.

Sid

well, if they could get the air time. Perhaps I answered my own question. My sister is a Physics Professor at a Community College and she is also a repuke. If I talked to her I would show here your post and see if she got the clue. Maybe I will e-mail it to her. :evilgrin:

:)

Sid

When we made those first two bombs the processing of the uranium to make the weapon's materials consumed roughly 10% of all of the electrical energy produced in the United States during its production. Got that? Our chains of compressors were located in K-25, Oak Ridge, TN under a building roughly the size of any small town. You simply could not possibly build a similar facility anywhere on earth undetected. It would be roughly as hard to hide as a fart in a phone booth.

Might as well mention something else while the subject is hot. Yellow-cake. Yellow-cake, which is where the whole Plame affair began, is simply uranium ore at a just about the very lowest stage of refinement. It hasn't even been cast into metal ingots yet. You know the iron ore that filled the tanker Edmond Fitzgerald when it sank? Well, the stuff she carried was processed to about the same degree as Yellow-cake. Its just one step above raw ore and it takes a hell of a lot of it. Yellow-cake in the amounts needed to end up with a kilo or so of finished HEU (Highly Enriched Uranium) litterly fills freight trains - long ones. In trucks on the roads of anywhere from north Africa to the Gulf carrying that stuff in the amounts needed wouldn't very likely go undetected. It would probably almost equal the sheer volume of marijuana smuggled into the US every year.

One other point you failed to mention were naval nuclear reactors, which due to their small size, require weapons grade uranium in order to be viable for use in a maritime platform. It could be possible that if Iran was pursuing weapons grade uranium that they wanted it in order to upgrade their naval capabilities. Furthermore the best defense against potential American first strikes is an undetectable launch platform (along with nuclear warheads), the best choice there being an atomic powered ballistic missle launching submarine.

but that's more of an issue of "why" rather than "how". My thoughts were that it would be exceptionally difficult for Iran to secretly build the facilities and the power supply needed for full-blown production of quanties of HEU.

I think what you're saying is that there is another reason, other than weapons, for them to produce HEU, so they might not have to do it in secret. I hadn't thought of that.

Sid

However they would have to construct the nuclear plant on top of the enrichment facility and provide power that way. But since they don't even have enough centrifuges to make signifigant enrichment levels of uranium... I dunno, it's good to know that the reasons for any current action against Iran are BS and have scientific proof. My personal background is more on the operational side of the nuclear pipeline, rather than the fabrication.

Oh yeah, U-238 has a thermal microscopic cross section of 2.68 barns, while U-235 has close to 600 barns. Which if you performed a proper fuel loading could be used to make fairly strong quantities of Pu-239 due to the beta-minus decay reaction of U-239 being the most probable mode of decay and having a relativly short half life of a few hours. Then again Pu-239 bombs are more difficult to make due to the extra quantity of material, explosion physics, and detonator sophistocation involved.

Also, because the GD process was taking a long time to set up, another approach was pursued -- isotope separation by mass spectroscopy. Thousands of "calutrons" were built, using electromagnets built with silver wire (silver is a better conductor than copper) taken from US Treasury holdings in Fort Knox. This is an absurdly energy-inefficient approach, but the US pursued every approach simultaneously just to be sure of success. Gas centrifuges seem to be favored now; not sure whether it's because of greater efficiency, lower expense (for setup), or smaller size. But one should be cautious of comparing modern enrichment programs with the original process -- the best methods available today are sure to be a big improvement on a wartime, no-expense-too-great, crash program.

ON EDIT: Check out Richard Rhodes' "The Making of the Atomic Bomb". It's got so much detail it's scary. (Also "Dark Sun" for the H-bomb.)

recommend the ERD NOW . . here:

http://www.democraticunderground.com/discuss/duboard.php?az=nominate&forum=203&thread=422803