Iran steps over the line on nukes — what’s the next step for Trump?

Just what is enriched uranium? Iran said Monday it has exceeded a key limitation on its stockpile, to which it had agreed in 2015 as part of the Joint Comprehensive Plan of Action (JCPOA). A fierce policy debate on what to do about Tehran’s behavior is in prospect. 

To understand at least some of the technical issues, the following is a layperson’s guide:

The nuclear physics: Natural uranium combines two slightly different types, known as isotopes. For every thousand atoms, 993 of those are uranium-238 and the other seven are uranium-235, a slightly smaller-sized particle. Enriching uranium means increasing the proportion of uranium-235 by getting rid of uranium-238 atoms. 

Starting from the proportion of 993-to-7, when the ratio becomes 190-to-7 the material is said to 3.67 percent enriched. This uranium is suitable for many power reactors and is, or at least has been, one of the limits to which Iran agreed under the JCPOA.  

The engineering: The most efficient way to enrich is by using high-speed centrifuges. Think of a top-loading washing machine, although perhaps only nine inches in diameter and much taller, around six feet. Water is squeezed out of the laundry by spinning. In a centrifuge, the slight difference in weight of the uranium isotopes causes them to separate during the spinning. Repeated multiple times, through groups of machines known as cascades running 24/7, enrichment is achieved.

Making an atomic bomb: Simply put, the greater the time spent spinning, the greater the enrichment. A rule of thumb is that 5,000 centrifuges of the basic type used by Iran, known as IR-1, will produce enough enriched uranium for one bomb in six months. Enrichment level for a bomb is 90 percent — meaning the ratio of uranium-238 to uranium-235 has switched from 993:7 to 1:7.

How much uranium-235 is needed for one bomb? The answer is about 55 pounds, the size of a large grapefruit. But the more interesting question is: How much natural uranium is needed to produce this amount of enriched uranium? That answer is about 10,500 pounds. Iran has its own reserves of natural uranium, which can be mined, so acquiring this is not a particular problem for Iran.

Iranian Foreign Minister Mohammad Javad Zarif told the news agency ISNA that the country has gone beyond an agreed limit of 660 pounds (300 kilograms) of low enriched uranium, a figure that includes uranium compounds such as uranium hexafluoride, which in gaseous form is used as feedstock in centrifuges.

Also in prospect is an Iranian announcement to enrich to 20 percent, a ratio of the uranium isotopes of 35:7 — disturbingly close to the level needed for a nuclear weapon.

Yet another possibility is that Iran may withdraw from the Nuclear Non-Proliferation Treaty (NPT), which it signed up to during the shah’s era, which entitles it to peaceful nuclear technology in return for forsaking nuclear weapons. (Tehran officially claims, implausibly, that it has never had a nuclear bomb project. Withdrawing from the NPT does not, as such, contradict this position, but it does free Iran from the treaty’s constrictions.)

How can Washington respond? The Obama administration, ridiculed now by the Trump White House for agreeing to the JCPOA, at one point worked with the Israelis to sabotage Iranian centrifuges using the Stuxnet computer program. This had an effect similar to one turning off and on a washing machine in mid-cycle. But that merely delayed, rather than stopped, Iranian engineers.

At the very least, the International Atomic Energy Agency, the world’s nuclear watchdog, should be pressured to conduct closer inspections of Iranian sites. (I was once given a tour of an enrichment plant; it could fit in a building the size of many U.S. neighborhood supermarkets.) Also, the IAEA should monitor more closely the Iranian capacity to produce plutonium, technically superior to highly enriched uranium as a nuclear explosive but more challenging to obtain.

President Trump appears to be putting his faith in sanctions, rather than military action. The battleground for the immediate future may turn out to be Twittersphere, with Iranian pronouncements vying with presidential tweets to win public support.

The latest surprise ingredient perhaps is President Trump’s weekend meeting with North Korean leader Kim Jong Un. The North Koreans have a far more advanced nuclear program than Iran’s, having mastered both uranium enrichment and plutonium reprocessing, tested weapons several times, and developed missiles capable of carrying such warheads as far as the continental U.S.

These are all skills that the U.S. tried but failed to stop Pyongyang from acquiring. Supreme Leader Ali Khamenei in Tehran may be hoping that his country can persevere through sanctions and other pressures to win a similar level of achievement. It is doubtful, though, whether he wants to develop a Kim-style personal relationship with Trump.

Simon Henderson is the Baker Fellow and director of the Bernstein Program on Gulf and Energy Policy at the Washington Institute for Near East Policy. Follow him on Twitter @shendersongulf.