Despite Threat to Breach Limits, Iran Remains Below the Nuclear Deal’s Caps

The International Atomic Energy Agency’s (IAEA) most recent report on Iran’s implementation of the 2015 multilateral nuclear deal indicates that Tehran continues to adhere to the accord’s limits—a positive development after President Hassan Rouhani announced that Iran would reduce compliance with the agreement.

Specifically, the Supreme National Security Council stated May 8 that Iran would no longer be bound by the stockpile limits on heavy water and low-enriched uranium (LEU) put in place by the nuclear deal, known as the Joint Comprehensive Plan of Action (JCPOA). According to the May 31 IAEA report, Iran remains below those caps—for now (see below for details). 

While it is positive that Iran appears to be exercising restraint and remaining in compliance with the JCPOA, its threats to violate the deal jeopardizes the future of the accord and risks reigniting a nuclear crisis. Similarly, attempts to exploit ambiguities and test the boundaries of the agreement—which Iran may be doing by installing additional advanced IR-6 centrifuges for research—are unhelpful (see below for details).

Iran’s threat to exceed limits set by the deal—made one year after U.S. President Donald Trump withdrew from the JCPOA and reimposed sanctions despite Iran’s compliance with the accord—was a predictable but worrisome response to the Trump administration’s campaign to systematically deny Tehran any benefit of remaining in compliance with the agreement. While Iran’s frustration with Trump's reckless and irresponsible pressure campaign is understandable, it remains in Iran’s interests to continue meeting its obligations under the JCPOA, cooperating with the IAEA, and working with the remaining parties to the deal to facilitate legitimate trade that bypasses U.S. sanctions.

Details from the May 31 IAEA Report

Low-Enriched Uranium Stockpile Remains Below Limit

The IAEA noted that Iran’s stockpile of uranium enriched to 3.67 percent uranium-235 was 174.1 kilograms as of May 20, a slight increase from the 163.8 kilograms recorded by the agency in February, but below the JCPOA’s limit of 202 kilograms (which corresponds to the quantity of uranium in 300 kilograms of 3.67 percent enriched uranium hexafluoride gas).

Iran could breach the LEU limit within weeks if Tehran decides to maximize the production capacity of the 5,060 IR-1 centrifuges allowed for enriching uranium under the JCPOA. Exceeding the limit of uranium enriched to 3.67 percent would reduce the so-called breakout time, or the time it takes Iran to produce enough fissile material for a nuclear weapon (currently around 12 months due to the nuclear deal). However, slightly breaching the 300-kilogram limit would not be an immediate proliferation risk, as Iran would need roughly four times that amount of uranium hexafluoride gas enriched to 3.67 percent to produce enough weapons-grade material (more than 90 percent enriched uranium-235) for one bomb.

Heavy Water Stocks Remain Below Limit

According to the IAEA report, Iran’s stockpile of heavy water was 125.2 metric tons as of May 26, below the 130 metric ton limit set by the deal. The stockpile is up slightly from the 124.8 metric tons reported by the IAEA in February.

Iran has the capacity to produce about five metric tons per quarter, but the IAEA noted that the heavy water production plant had been shut down from April 15-May 22. Iran also reported that it used two metric tons of heavy water since February for research activities overseen by the IAEA.

Given Iran’s heavy water production capacity, it is likely that Iran could breach the 130-metric-ton limit by the IAEA’s next report in late August. While any violation of the deal’s limits is a concern, excess heavy water does not pose a proliferation risk as it would be used to moderate Iran’s reactor at Arak, which remains unfinished.

IR-6 Advanced Centrifuge Installation Raises Questions

The IAEA report raises questions about whether Iran’s decision in April to install 20 additional IR-6 centrifuges at Natanz is consistent with limits set by the JCPOA and its accompanying confidential research and development plan submitted to the IAEA.

The IAEA reported that Iran has installed 33 IR-6 machines, of which 10 have been used for testing with uranium, and said that “technical discussions” regarding the IR-6 are ongoing.

According to the JCPOA, Tehran can test the IR-6 using “single centrifuge machines and its intermediate cascades.” The deal does not specify what constitutes an “intermediate cascade,” but states that after eight and a half years (July 2024), Iran can “commence testing of up to 30 [IR-6] centrifuges machines.” (JCPOA, Annex I, Section G, Paragraph 38.) Uranium can be fed into the test machines, but Iran cannot withdraw any enriched material.

An alleged copy of Iran’s confidential research and development plan leaked to the Associated Press in 2016 suggests that Iran can move from testing a cascade of about 10 IR-6 machines to a cascade of 20 machines approximately halfway through the eight-and-a-half-year period after implementation day, around April 2020.

While testing 10 IR-6 centrifuges with uranium appears consistent with the JCPOA and reporting on the leaked research and development plan, neither document appears to specify that Iran can install additional IR-6 machines. Iran may be trying to exploit ambiguities in the text to argue that it can have additional IR-6 machines installed but not operating. If the language is ambiguous, ideally the Joint Commission set up by the JCPOA to oversee its implementation will make a determination. But given the current tensions surrounding the JCPOA, attempts by Iran to push the limits on interpreting the text of the agreement risks further destabilizing the deal.

Additional Details

Iran also threatened May 8 to resume enrichment to levels above 3.67 percent uranium-235 and restart work on the unfinished heavy-water reactor at Arak after 60 days (around July 7), if the remaining parties to the deal are unable to facilitate sales of Iranian oil and banking transactions. The IAEA report states that Iran has not resumed work at Arak or enriched uranium above the 3.67 percent uranium-235 allowed by the JCPOA.

The IAEA report also noted that:

  • Iran is operating no more than 5,060 IR-1 centrifuges at the Fuel Enrichment Plant at Natanz and is enriching uranium to no more than 3.67 percent uranium-235, as required by the JCPOA. Since the last IAEA report, Iran withdrew 52 IR-1 centrifuges to replace broken machines.
  • Iran continues to provisionally implement the additional protocol to its IAEA safeguards agreement.
  • Inspectors have had access to all the sites in Iran that they have needed to visit.
  • Iran is adhering to the limit of 1,044 IR-1 centrifuges installed at the Fordow site and is conducting stable isotope research and development at that facility in line with JCPOA requirements.