November 27, 2020

The Majlis has approved a law requiring the Atomic Energy Organization of Iran (AEOI) to produce at least 120 kilograms of 20 percent enriched uranium annually at the Fordo nuclear site.

The Joint Comprehensive Plan of Action (JCPOA) limits enrichment to 3.67 percent.  Since breaching that cap, Iran has enriched uranium up to 4.75 percent.  If Iran does enrich to 20 percent, that means it will be 97 percent of the way to 90 percent enrichment, which is the preferred level for nuclear weapons.

The new law also requires the activation of 1,000 IR-2M centrifuges in the underground section of the Natanz nuclear facility, the installation and activation by April 2021 of 1,000 advanced IR-6 centrifuges at the Fordo nuclear site and the immediate reactivation of the IR-40 Arak heavy water reactor facility.  The only centrifuges Iran has been using until now are the old and slow IR-1 models.  The JCPOA doesn’t allow newer and better models to be used now.

The legislation is a “major step” that will “force” the United States and the European Union to revoke their sanctions against the Islamic Republic, according to a report on state television.

The law also calls for Iran to stop its voluntary implementation of the Additional Protocol—which gives the International Atomic Energy Agency (IAEA) access to many locales in Iran—if banking relations with Europe and the volume of oil purchases by the EU does not return to pre-sanctions levels.

If the parties to the 2015 nuclear deal fulfil their undertakings, the government is required to submit a proposal to the Majlis for Iran’s reciprocal action, the new law states.  That means that the Rohani Administration could not automatically resume compliance with the JCPOA if the Biden Administration rejoined the agreement

But why is enrichment to 20 percent a full 97 percent of the way to 90 percent enrichment?  That sounds counter-intuitive.

The answer is that the hard work of enrichment comes at the start of the process; it gets much easier the further along one goes.

The table below shows what is involved to reach weapons-grade.

Natural uranium contains only 0.7 percent U-235, the type of uranium needed for weapons.  Most of natural uranium is U-238, which is useless for weapons purposes.

“Enriching” uranium involves getting rid of excess U-238 and concentrating the amount of U-235.  A centrifuge spins at great speed to spin off the heavier U-238 atoms and leave the lighter weight U-235 atoms.

The first line of the table below shows 1,000 atoms of natural uranium split between 7 atoms of U-235 and 993 atoms of U-238.

At its Natanz plant, Iran’s centrifuges spin for long periods to get rid of 800 atoms of U-238.  The result is 200 atoms remaining of which the original seven U-235 atoms are now 3.5 percent of what remains.

Centrifuges can then take 3.5 percent enriched uranium and spin some more in order to get rid of another 164 atoms of U-238.  That leaves just 36 remaining atoms of which the original seven are U235 or just short of 20 percent.

The last line shows that only 28 more atoms of U-238 need to be spun-off in order to reach 90 percent enrichment or weapons-grade uranium.

Eighty percent of the effort needed to reach weapons-grade was expended just going from natural uranium with 0.7 percent U-235 to 3.5 percent enrichment, which is the concentration needed for a plant generating electricity.

Another 17 percent of the effort to reach weapons-grade is expended in the second step to reach 19.75 percent concentration—the concentration required for the small Tehran reactor that makes medical isotopes.

At that 19.75 percent concentration, the centrifuges have already spun off 97 percent of all the useless U-238 atoms.  Only another very small effort—amounting to just 3 percent of all the effort needed—is required to go the remainder of the distance and produce weapons-grade material of 90 percent U-235.

Uranium enrichment

U-238          Total           U-235          U-238              %

Spin-off      atoms          atoms          atoms          U-235

Natural       —                1000               7             993               0.7  %

Natanz        800               200               7             193               3.5  %

Fordo          164                 36               7               29             19.75%

?                28                   8                7                  1             90     %

To reach weapons-grade:

Spin off 800 =   80% of effort

“     “    164 =   17%  “      “

“     “      28 =     3%   “      “

Total      992 = 100%  “      “