On Monday January 4, Iranian government spokesman Ali Rabii announced the resumption of 20% uranium enrichment activities at the Fordo underground plant, located near the city of Qom, 180 kilometers away. south of Tehran. A few days earlier, on December 31, Tehran had already notified the International Atomic Energy Agency (IAEA) of its willingness to wait for this degree of enrichment of uranium in isotope 235.
This level is well above the threshold of 3.67% set by the Vienna agreement, which had already been violated before: on July 8, 2019, a spokesperson for the Iranian atomic energy organization announced that he had “Passed the 4.5% threshold for uranium enrichment”.
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Return to a previous level of enrichment
By reaching the percentage of mineral enrichment practiced six years ago, before the Vienna agreement, Iran is seriously damaging the joint action plan (JCPoA, Joint comprehensive plan of action), wrested in a fierce struggle in July 2015 after twelve years of diplomatic negotiations in order to guarantee the peaceful (that is to say civilian) nature of the Iranian nuclear program.
However, the main objective of the group called “P5 + 1” (United States, Russia, China, France, United Kingdom and Germany) was first to put in place severe restrictions to ensure that the “Breakout time”, the time necessary to produce the quantity of enriched uranium necessary to manufacture an atomic weapon, ie at least one year over a period of ten years. Before signing, it was estimated to be a few weeks.
The agreement had already been strongly weakened by the unilateral defection of the United States, which, in May 2018, had preferred to reinstate economic sanctions. Through its uranium enrichment activities, two weeks before the end of the mandate of US President Donald Trump, Iran is trying to put pressure on the future administration of Joe Biden, with a view to a return of the United States. United in the agreement.
From “yellow cake” to enriched uranium
Relatively abundant, uranium is in fact essential for various civil and military nuclear techniques. The uranium atom exists in two forms, which differ only in the number of neutrons in their nucleus: they are isotopes. In its natural state, the uranium that is extracted is composed of more than 99%, by mass, of uranium 238 (which is written 238U) and 0.7% uranium 235 (235U). Only this last isotope allows a nuclear fission reaction.
To be used as fuel in a nuclear power plant and to produce energy – and even more so to be used in the manufacture of a bomb – uranium must be enriched. Extracted from mines, uranium is crushed and mixed with different products to release it in a more concentrated and more easily transportable form, called “Yellow cake” (yellow cake). It is then that the enrichment phase can begin.
The most common method is to inject uranium in gaseous form into a centrifuge. Isotope 235U being lighter than 238U (because it has three neutrons less), the separation between the two isotopes can take place. But for the content of 235When the desired proportion is reached, the process must be repeated many, many times. This is why the centrifuges are mounted in cascade: the gas passes through successive machines and increases its concentration.
Easier to go from 20% to 90% than from 3% to 20%
The process is long and tedious, in particular to reach the bar of the first twenty percent of enriched uranium. This threshold, which the Iranian Atomic Energy Organization (OIEA) claims to have reached on January 4, is symbolic: “Enriching uranium by 20% to 90% – which is the level required for a nuclear weapon – is much easier and faster than enriching it by 3% to 20%”, summarizes François Nicoullaud, former French Ambassador to Tehran and specialist in Iranian issues.
According to a law adopted on 1er December 2020 by the Iranian Parliament, the objective is to produce and store at “Less 120 kilograms per year of 20% enriched uranium”. However, to obtain a significant quantity of enriched uranium, it is necessary to have several thousand centrifuges. The Vienna Agreements had provided that Iran would keep only part of the centrifuges then in its possession – old models “Obsolete”, according to Mr. Nicoullaud. Since then, Tehran has however developed and installed new generation centrifuges.
A first version of this article was published on July 10, 2019, when Iran announced that it had exceeded the threshold set by the Vienna agreement.
