Friday, April 03, 2015

CNN Botches Uranium Enrichment Numbers

CNN logoEarlier today, the CNN network crawler put out incorrect information about Iran’s uranium enrichment.

The crawler stated that 3.67% is "roughly halfway to weapons grade." That is off by several magnitudes. The cited figure is actually well within the range of reactor grade, magnitudes away from weapons grade. Weapons grade uranium is enriched to at least 85%-90% U235, the fissile element.

Quoting the Smithsonian, "U-235, however, is fissile; it can start a nuclear reaction and sustain it. The 0.7% in naturally occurring uranium is not enough to make a bomb or even a nuclear reactor for a power plant. A power plant requires uranium with 3-4% U-235 (this is known as low-enriched or reactor-grade uranium).

Most importantly, a nuclear bomb needs uranium with a whopping 90% U-235 (highly enriched uranium)."

Here are our tweets reacting to this major error:








Indeed, facts matter.

UPDATE: NEI's Tom Kauffman just reached out with this additional comment:

It is physically impossible for a U.S. commercial reactor to explode like a nuclear weapon. The concentration of uranium-235 within the reactor fuel (3% to 5%) is far too low to be explosive and all U.S. commercial reactors are self-limiting. During power operations, when the temperature within the reactor reaches a predetermined level, the fission process is naturally suppressed so the power level cannot spike under any circumstances. And, by design, no one could intentionally or unintentionally alter a commercial nuclear reactor, its controls or its fuel to make it explode like a nuclear weapon.

A good reminder.

8 comments:

Bill said...

Doesn't seem off-the-wall to me.
According to the WNA, it takes 800 SWUs to enrich a ton of natural uranium to fuel grade, and 1300 SWUs to weapons-grade.

"The curve flattens out so much because the mass of material being enriched progressively diminishes to these amounts, from the original one tonne, so requires less effort relative to what has already been applied to progress a lot further in percentage enrichment. The relatively small increment of effort needed to achieve the increase from normal levels is the reason why enrichment plants are considered a sensitive technology in relation to preventing weapons proliferation, and are very tightly supervised under international agreements. Where this safeguards supervision is compromised or obstructed, as in Iran, concerns arise." http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Conversion-Enrichment-and-Fabrication/Uranium-Enrichment/

SteveK9 said...

Sadly we've become a 'war' country. We push for war, no matter what the question might be.

Pavel Podvig said...

It's not an error at all - in terms of separative work, 3.67% could well be half-way, depending on a number of choices regarding feed, tails assay, etc.

Jim Van Zandt said...

And if I remember correctly, enriching from 0.7 to 5 is much easier than from 70.7 to 75.

Anonymous said...

Enrichment is an exponential process with each cascade providing a fractional improvement. going from 0.72% -> ~5% is "about" half the SWU/ centrifuge stage required to get to HEU.

the same number of stages required to get to 5% would take 5% to 35%...




jimwg said...

NEI. PLEASE do an in-depth examination of nuclear energy and the media. I can't plead plainer than that about a hot-potato issue to most all nuclear blogs or orgs.

Gutsy thanks!

James Greenidge
Queens NY
(who witnessed shameful media lynching of Shoreham)

Anonymous said...

How many SWU are needed to enrich one kilogram of uranium from natural (0.7% U-235) to 3.7% U-235? Then, how many additional SWU are needed to go from 3.7% to 90%?

That's the question, and the answer is not intuitive.

Hint: It's not linear -- less SWU are needed to increase enrichment as the enrichment level of the original feed increases.

CNN might still be wrong; it seems unlikely that 3.7% is fully "half way" to 90%. But it's not directly proportionate to the percentage of enrichment.

Also, it's important to bear in mind that one need not have weapons-GRADE uranium (>90%) to make a nuclear bomb. Any high-enriched uranium (>20%) can be used; it's a question of the size of the critical mass. That's why HEU exists as a category in safeguards nomenclature in the first place.

Edwin Lyman said...

I'm sorry, but I don't understand the point of your objection.

CNN is referring to the relative quantities of separative work required to enrich natural uranium and 3.67%-enriched uranium to weapons-grade. In fact, 3.67% is more than halfway in terms of SWU requirements. It takes approximately 36% as many SWU to produce a given quantity of 90%-enriched HEU from 3.67%-enriched LEU as it takes to produce the same quantity from enriching natural uranium.

Moreover, nuclear weapons can be built with much lower enrichments. The technical definition of HEU is any enrichment greater than 20%. There are tradeoffs between the enrichment and the core weight, however.