Explaining Bibi's Red Line (With a Bit of H.S. Chem.)

Uranium enrichment: Reaching the 20% U235 is the uphill-tough-sledding part. To then go from 20% U235 to 90% U235 is really the downhill-easy-run part. And Israel is a one bomb country.

Mark Langfan

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Mark Langfan
Mark Langfan

This essay will attempt

1) to explain what Bibi’s Iranian “Red-Line” actually means,

 2) to show why Bibi's Iranian Red-Line is reasonable, and

 3) enable a reader using only trivial math to actually calculate the Iranian Red-Line status from the newspaper. To do this, one needs to first see what Bibi has actually said, read some additional news reports and expert analysis, and then add some basic high school chemistry principles.


1. On January 11, 2012, former IAEA Iranian weapons expert Mr. Olli Heinonen, wrote in an article titled “The 20 Percent Solution”:

“Over the last few days, Iran has begun operating two enrichment cascades at Fordow. Furthermore, Iran is completing installation of two additional cascades, with their planned operation already announced. Once the four cascades at Fordow, in addition to the two Natanz ones, are operating, Iran will be able to produce 15 kg of 20 percent enriched UF6 (uranium hexafluoride) per month. This process uses as feed 3.5 percent enriched uranium, which is produced currently at a rate of 140 to 150 kg UF6 per month at Natanz.”. .

“If Iran decides to produce weapons-grade uranium from 20 percent enriched uranium, it has already technically undertaken 90 percent of the enrichment effort required. What remains to be done is the feeding of 20 percent uranium through existing additional cascades to achieve weapons-grade enrichment (more than 90 percent uranium). This step is much faster than the earlier ones. Growing the stockpile of 3.5 percent and 20 percent enriched uranium, as Iran is now doing, provides the basic material needed to produce four to five nuclear weapons. With IR-1 centrifuges, it would take half a year to go from 3.5 percent enriched uranium to weapons-grade material for the first nuclear device. More advanced centrifuges would cut the time required in half. If, however, IR-1s are using 20 percent enriched uranium as a feed, 250 kg UF6 with that level of enrichment can be turned to weapons-grade material in a month's time.”

2. On September 27, 2012, PM Netanyahu said at the UN General Assembly:

“This is a bomb; this is a fuse. In the case of Iran’s nuclear plans to build a bomb, this bomb has to be filled with enough enriched uranium. And Iran has to go through three stages. The first stage: they have to enrich enough of low enriched uranium. The second stage: they have to enrich enough medium enriched uranium. And the third and final stage: they have to enrich enough high enriched uranium for the first bomb. Where’s Iran? Iran’s completed the first stage. It took them many years, but they completed it and they’re 70% of the way there. Now they are well into the second stage. By next spring, at most by next summer at current enrichments rates, they will have finished the medium enrichment and move on to the final stage. From there, it’s only a few months, possibly a few weeks before they get enough enriched uranium for the first bomb.”

3. Iran has disclosed to the International ATOMIC Energy Agency (IAEA) and which the IAEA has confirmed, in the IAEA Board of Governors Report dated 30 November 2012, the IAEA stated:

“10. Since Iran began enriching uranium at its declared facilities, it has produced at those facilities approximately:

• 7611 kg (+735 kg since the Director General’s previous report) of UF6 enriched up to 5% U-235, of which: 5303 kg is presently in storage; 1226 kg has been fed into the Pilot Fuel Enrichment Plant (PFEP) and 1029 kg has been fed into the Fordow Fuel Enrichment Plant (FFEP) for enrichment up to 20% U-235; and 53 kg has been fed into the Uranium Conversion Facility (UCF) for conversion to UO2; 14 and 232.8 kg (+43.4 kg since the Director General’s previous report) of UF6 enriched up to 20% U-235, of which: 134.9 kg is presently in storage; 1.6 kg has been downblended; and 96.3 kg has been fed into the Fuel Plate Fabrication Plant (FPFP) for conversion to U3O8.15.”

4. On February 10, 2013, Myra MacDonald and Fredrik Dahl reported in Reuters the following:

“While scientists differ about how much uranium is needed to have the ability quickly to make a bomb, analysts say the Israeli figure is believed to be 240 kg of uranium enriched to 20 percent; at that concentration, the material is nine tenths of the way to the weapons-grade of about 90 percent, since most of the unwanted isotopes have been separated out by then.”

“’Israeli officials, in private, widely use the 240 kg figure,’ said Shashank Joshi, a Research Fellow at Britain’s Royal United Services Institute (RUSI). ‘The figure is so specific and so widely used that they must understand the implications of drawing this red line: that Iran is free to produce anything up to that amount, but that producing any more would force Israel to choose between humiliation or war.’”

5. On February 18, 2013, PM Netanyahu further explained that:

“They say it. They move forward. They’re progressing. They’re getting closer to the red line that I had set at the UN. They’re building rapid centrifuges: that is centrifuges that enrich uranium needed to make nuclear bombs at three times the pace so that they could cross that red line and get to a high enrichment to a sufficient amount of 90% enriched uranium within a much shorter time. They’re doing all that. So far, they’ve not been stopped. And the sanctions themselves – even tougher sanctions – will not stop them.”

6. Finally, on February 21, 2013, BBC News reported that:
“Iran had informed the IAEA in a letter on 23 January that it planned to introduce a new model of centrifuge called the IR2m, which can enrich two or three times faster than current equipment.”

Explanation and Analysis:

Given these news reports, in short, Bibi clearly meant his “Red-Line” to mean Iran’s having 240 kilograms of Uranium Hexafluoride (UH6) gas enriched to a 20% U235 level (“medium enriched uranium”) so that the Bibi-described “second stage” would be “completed.”

“Completed,” as Bibi meant it, in the sense that there would be enough of the medium enriched uranium 20% U235 stockpile from which the Iranians could then quickly further enrich enough 90% U235 enriched uranium (“highly enriched uranium”) to arm one uranium Hiroshima-type gun-type nuclear bomb.

Therefore, given this further information, more specifically, this article will attempt to explain why Israeli Prime Minister Netanyahu considers his Iranian "Red-Line" to be Iran's having stockpiled approximately 240 kilograms (kgs) of UF6 Uranium Hexafloride gas where the UF6 gas containing 20% U235 isotope/80% of the U238 isotope, and why Bibi’s Iranian Red-Line is reasonable.

Remember, U235 is the uranium isotope that is more atomically “fragile” than its U238 cousin, and hence, good for making a uranium gun-type nuclear bomb. Consequently, it is bad for Iran to have enriched that much of the specific U235 isotope to a much higher pre-weapons-grade 20% concentration.

So, what is 240 kgs of UF6 gas containing 20% U235? And why is this amount of stockpiled UF6 gas the likely magic "Red-Line" across which Israel fears Iran will quickly obtain a nuclear bomb?

Let’s get really basic. What does "UF6 20% U235" mean to begin with?

 Firstly, UF6 gas is the gaseous medium through which one relatively easily enriches and separates the various uranium isotopes from each other by spinning the UF6 gas containing the mixed uranium isotopes through high speed centrifuges. In nature, mined naturally occurring uranium ore usually contains about combined average amounts of .7% of U235 and 99.3% of U238. The enrichment goal for a nuclear bomb is to change the natural state of uranium from low235/high238 to weapons-grade state of high235/low238 by repeatedly, in a cascade, separating and enriching the higher grade of U235. When mined in nature, the relative percentages of natural uranium containing both U235 and U238 isotopes is about 1 U235 atom for every 150 U238 atoms. After high level enrichment to the weapons' grade, the ratio is approximately 10 U235 atoms for every 1 atom of U238.

How difficult is it to first enrich UF6 with .7% U235 to UF6 with 20% U235? And then how hard to go from 20% U235 UF6 to 90% U235 UF6?

To accomplish this enrichment of the U235 uranium isotope, the atomic scientists chemically bind one uranium atom to 6 fluoride atoms which then becomes Uranium Hexafluoride or UF6 gas (which stands for one atom of Uranium for every six atoms of fluoride which form one molecule of Uranium Hexafluoride) under certain pressures. In the gaseous UF6 form, the heavier and lighter uranium isotopes are easier to separate from each other by spinning the UF6 gas in high-speed centrifuges. In this process of enriching the U235 isotope from its heavier U238 isotope cousin, the original UF6 gas first contains the same U235/U238 ratio as natural uranium. But as the enrichment process proceeds, the enriched UF6 gas slowly contains a much greater ratio of U235 to U238 and hence a greater percentage of the UF6 contains the U235 atom.

Bibi’s “low enriched uranium” is 3.8% U235 UF6 gas. Bibi’s claim that once the “medium enriched uranium” level of 20% U235 UF6 gas has been reached, 90% of the total enrichment effort necessary to bring the uranium from .7% to weapons’ grade 90% U235 has been expended, jibs exactly with Mr. Heinonen’s published January 2012 analysis. Again, Mr. Heinonen stated that once the 20% U235 enrichment has been achieved, Iran “has already technically undertaken 90 percent of the enrichment effort required” to “produce weapons-grade uranium.” That's because, anti-intuitively, to go from .7% U235 to 20% U235 enriched uranium takes 90% of the total enrichment effort. But for the enrichment process to go from 20% U235 to 90% U235, it takes only 10% of the total enrichment effort.

 In short, reaching the 20% U235 is the uphill-tough-sledding part. To then go from 20% U235 to 90% U235 is really the downhill-easy-run part.

What makes uranium, U235? Or uranium, U238? And, how is the difference exploited in enrichment?

 So, 20% U235 UF6 gas really just means 20% of the UF6 gas contains the lighter U235 uranium isotope, and 80% of the UF6 gas contains the heavier U238 uranium isotope with the 3 extra neutrons in its nucleus. Both the U235 and U238 isotopes still both have 112 protons, U238 just has 3 extra neutrons where each extra neutron weighs about one atomic mass unit (AMUs). So the atomic weight of the U235 isotope is about 235 AMUs for each molecular unit of U235; the atomic weight of the U238 isotope is about 3 AMUs heavier than U235 for a total 238 AMUs per molecular unit of U238. This is because each neutron weighs about one AMU. The nuclear scientists exploit this slight difference in atomic weight between U235 and U238 to separate the two isotopes and enrich the U235 to a weapons' grade uranium percentage of 90% U235/10% U238.

The mixed U235/U238 UF6 gas is fed into the high speed centrifuges where the UF6 gas molecules containing the heavier U238 isotope spin outward faster than the UF6 gas molecules containing the lighter 235 UF6 isotope. The heavier U238 UF6 gas molecules are sucked out of the outside rim of the centrifuge and reprocessed upstream, while the lighter U235 UF6 gas molecules are sucked out from the center of the centrifuge to be fed downstream into the next centrifuge to be yet further enriched.

How much weapons-grade 90% U235 can you get from a kilogram of UF6 20% U235 gas, or more specifically, from 240 kilograms of UF6 20% U235?

The reason I plied you with all this basic high school chemistry science (which you have probably not seen since then) is that it is a vital jigsaw piece to understanding the real debate. That's because the key thing to understand is: What exactly does 240 kgs of 20% U235 UF6 gas represent and get you in terms of net-net actual 90% U235 weapons-grade bomb-type uranium?

The key fact is the molecule of UF6 simply means one atom of uranium (either the U235 isotope or the U238 isotope) is bound to 6 atoms of fluoride. Since fluoride has an atomic weight of about 19 AMUs for each atom of fluoride, you multiply 6 times 19AMUs for about 120 AMUs worth of the element fluoride are in one molecular unit of UF6. Add the 120 AMUs of fluoride to the approximate 235-238 AMUs of the element uranium (mix of U235 and U238) atom and you get about 337AMUs of atomic weight for one molecular unit of UF6 gas. Hence, the fluoride represents about one-third the actual weight of the resulting UF6 gas, and the mixed U235/U238 isotopes of uranium represent about two-thirds of the actual weight of the resulting UF6 gas.

Consequently, we now apply this relative fluoride/mixed U235/238 uranium relative weight analysis to Bibi's Red-Line amount of 240 kgs of 20% U235 UF6 gas. So, you multiply 240 kgs of UF6 gas times 66% and that yields you about 160kgs of netted total mixed U235/U238 uranium where 20% is the U235 isotope and 80% is the U238 isotope. Therefore, you further multiply 160 kgs of the total netted uranium times 20% (or one-fifth) because the U235 is 20% of the total netted uranium. That net-nets you down to about 32 kgs of pure bomb grade U235. Since one only needs 90% U235 that means 160 kgs of 20% U235 net-nets you to about 35 kgs of 90% weapons-grade uranium. See graphic www.marklangfan.com/240kguh6bomb.html

It is widely assumed that you only need about 25-30 kgs of weapons-grade uranium to make one uranium gun-type Hiroshima type nuclear weapon. Hence in "nuclear proliferation lingo," 25 kilograms of 90% 235 uranium is called a "Significant Quantity" or “SQ" of weapons-grade uranium. Hence, you can make a quick calculation of the amount of weapons-grade U235 in any amount of 20% U235 UF6 gas by just multiplying the total 20% U235 UF6 gas kilograms by one-fifteenth or 1/15.

 How fast can 240 kg of UF6 20% gas be processed to get a bomb's worth weapons-grade U235?

In other words, what Bibi means by the "240 kgs of 20% U235 UF6 gas Red-Line” is if the Iranians get 240 kgs of 20% 235 UF6 gas, they can quickly spin and centrifuge that stockpiled gas out to make one nuclear bomb's worth of 90% weapons grade 235. To quote Mr. Olli Heinonen, the preeminent former IAEA nuclear weapons expert, if the Iranians are "using 20% enriched uranium as a feed [for the cascade of centrifuges], 250 kg of UF6 with that level of enrichment can be turned into weapon-grade material in one month."

How will the newly announced new generation of Iranian centrifuges affect this break out time?

What's worse is Iran announced the installation of a new generation of even faster and better centrifuges. Hence, the time needed to "breakout" from 20% U235 to the 90% U235 of one bomb’s worth of uranium to weapons-grade enrichment level would be about two weeks.

How much 20% U235 UF6 does Iran possess at this time?

So even assuming you believe the Iranians, and the IAEA, Iran had, as of 3 months ago, about 134.9 kgs of 20% UF6 stockpiled and ready to be spun to 90% U235 UF6 gas. The “diversion” of some of the 20% UF6 gas averted Iran from crossing what would have been Bibi’s Iranian Red-Line. Had Iran not voluntarily diverted 96.3 kg of their 20% U235 stockpile to fuel plate production, Iran would have already crossed the Bibi Red-Line. We don't really even know for sure if Iran diverted the U235 enriched UF6 gas. Let's just hope they did.

How much 20% 235 UF6 gas is Iran stockpiling per month?

As Mr. Heinonen stated, “once the four cascades at Fordow, in addition to the two Natanz ones, are operating, Iran will be able to produce 15 kg of 20% enriched UF6 (uranium hexafluoride) per month.” This “15 kg” a month number is field-confirmed because the IAEA report cites, “+43.4 kg since the Director General’s previous report,” which was 3 months before. So, the Iranian stockpiling rate of UF6 20% gas is about 15kgs a month.

After they get the 90% U235 UF6 gas, what do the Iranians need to do to actually build a final workable nuclear bomb?

Once the UF6 gas reaches the enriched 90% U235/10% U238, the atomic scientists then chemically decouple the uranium atom from the fluoride atoms to get a pure uranium metal of 90% U235 purity (10% U238). This is a technically trivial part of the process. It is this enriched metal that is then shaped, and put into the actual bomb mechanism, or "physic's package" as it is known. The Iranians are surely working on such an actual atomic bomb mechanism in parallel to their U235 enrichment so there isn't likely going to be a huge lag time at the final assembly phase where the enriched U235 metal is installed in the actual bomb mechanism. (And remember, in 1945, the US didn’t even test its first gun-type uranium bomb before it dropped it on Hiroshima. And, Iran has surely partnered with North Korea on its nuclear tests.)

Therefore, Bibi’s attempt to draw a Red-Line where Iran could be less than one month (or now two weeks) away from a nuclear bomb isn't war-mongering, but is peacemaking and prudent statesmanship. In fact, Bibi's line may even be too close to the point of no-return where Iran will one morning fire off a nuclear blast and tell the world it is a fully nuclear weapons' state.

And as Cong. Steve Southerland II(R-Fla.) correctly stated, “Israel is a one-bomb country.” So, even with one Iranian bomb, Israel’s very existence, along with its 6 million Jewish citizens, is at total risk.

For more information please visit http://www.marklangfan.com/