Here’s What the U.S. Is Trying to Do With the Iran Nuclear Deal

The Iran nuclear deal won’t stop the country’s ability to make a nuclear weapon, but it will give us more warning time

World Nuclear Association

Iran has the technological ability to produce nuclear weapons. Yet, so far as we know, they have not done so. In a deal worked out over the weekend Iran has agreed to temporarily honor sanctions on its nuclear program in exchange for roughly $7 billion in relief. The deal is the first big step in efforts to curb Iranian nuclear proliferation in years, but the restrictions are a temporary deal—the sanctions will last just six months, hopefully giving politicians time to work out a longer-term agreement.

First off, here’s what Iran didn’t agree to do: Iran did not agree to stop enriching uranium from uranium-238—the type of uranium primarily found in raw uranium ore—into uranium-235, the kind used in most nuclear reactors and bombs. This is seen, by some countries, as a failure to fully curb Iran’s nuclear potential.

Here’s what Iran did agree to doIran agreed to not build any more centrifuges, the equipment used for enriching uranium. Iran also agreed to limit the scope of its enrichment program. Natural uranium is around 0.7 percent uranium-235, and Iran still going to enrich uranium to around 3.5 to 5 percent uranium-235, the level used for nuclear reactors. But it’s going to stop making 20 percent enriched uranium-235, and it’s going to cut down on the stocks of 20 percent enriched uranium it already has.

The deal is sort of complicated, and doesn’t really make much sense unless you know a little bit about nuclear enrichment. This graph from the World Nuclear Association is actually super useful for understanding what the U.S. is trying to do with the nuclear deal, once you know how to read it.

Along the left axis of this graph is the amount of work that you need to do to enrich uranium, from the natural level around 0.7 percent up to 90 percent, the enrichment level needed for nuclear weapons. That effort is measured in SWUs, or separative work units, the amount of work it takes to separate uranium-235 out from uranium-238. From low levels of enrichment, on the left, up to high levels on the right, you can see the slope taper off. This means that once your uranium is already enriched a little bit, it takes less work to enrich it even more.

So, since enriching uranium gets easier the more you do it, the U.S. is worried about something called a “nuclear breakout.” That is, if Iran has a lot of uranium enrichment capability, in the form of centrifuges, and big stockpiles of 5 percent- and 20 percent-enriched uranium, it wouldn’t take them long at all to to push for a nuclear weapons-caliber 90%-enriched uranium, if they did decide to develop a weapon.

Here’s what the deal really does: By limiting the number of centrifuges the country has, and making it knock down its stockpiles of 20 percent enriched uranium, the nuclear deal adds time to Iran’s nuclear breakout potential. The country could still push for a weapon, but with its handicapped supplies and production facilities, it would take it longer to do so—giving the rest of the world more time to notice and react.

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