What is downblending, the process at the heart of Trump’s Iran agreement?
In the memorandum of understanding signed by the U.S. and Iran to end the war, Tehran has pledged never to develop a nuclear bomb in
In the memorandum of understanding signed by the U.S. and Iran to end the war, Tehran has pledged never to develop a nuclear bomb in return for U.S. sanctions relief and access to a $300 billion development fund. Beyond that commitment, the MoU offers few details on how the U.S. and Iran intend to solve the nuclear dispute. Iran still possesses hundreds of kilograms of highly enriched uranium and retains the technical capacity to produce more. While the modalities of a final agreement are to be negotiated in the second phase of talks, the MoU states that both sides have agreed to take steps to downblend Iran’s uranium stockpile. U.S. President Donald Trump said last week that the U.S. would “go and get” Iran’s highly enriched uranium “at some point” and “dilute” (downblend) it either in America or in Iran. Paragraph 8 of the MoU states: “The Islamic Republic of Iran reaffirms that it shall not procure or develop nuclear weapons... The two parties also agreed to resolve the disposition of stockpiled enriched material pursuant to a mechanism... with the minimum methodology to be down-blending on site under the supervision of the International Atomic Energy Agency.” Downblending is a technology used to make uranium less pure. It is difficult to purify uranium, and highly pure uranium can be used to make nuclear bombs. So downblending removes the amount of uranium-235 available to make a bomb and increases the time required to do so.
This duration, called the breakout time, is a cornerstone of modern nuclear non-proliferation. Thus, the international community’s trust in Iran’s promise to not pursue a nuclear weapon depends on how well it implements downblending in the coming months, among other factors. Uranium in nature consists mainly of two isotopes: uranium-238 and uranium-235. Of these, only uranium-235 is fissile, meaning it can sustain a nuclear chain reaction. However, the natural concentration of uranium-235 in uranium is only 0.72%. The remaining 99.28% is uranium-238. Purification means enriching the concentration of uranium-235 to higher levels. Downblending is the opposite of enrichment. Here, enriched uranium is mixed with depleted (opposite of enriched) or natural uranium to produce uranium with less than 5% uranium-235. E.g. the 2015 Iran deal allowed Iran to enrich uranium up to 3.67%. Uranium of this purity can be used in some simple reactors to produce electricity but not to make a bomb. The enriched uranium feedstock is usually stored as the compound uranium hexafluoride (UF6), which is a solid at room temperature. In the first step, the steel cylinders containing UF6 are placed in an industrial oven called an autoclave and heated to 80-110° C, turning the compound to gas. Gases are easier to mix than solids. Second, another source of uranium called the blendstock is prepared. It can have 0.7% uranium-235 (natural uranium), 0.2-0.3% (depleted uranium), 1% uranium-235 (slightly enriched) or a different level.
The BriefWire