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– Larry Weiler
Former U.S.-Russian arms control negotiator
August 7, 2018
Iran Raising Uranium-Enrichment Level

Peter Crail

Iran has moved nearly its entire stockpile of low-enriched uranium (LEU) to a plant where it has begun further enrichment to up to 20 percent, a Feb. 18 report by the International Atomic Energy Agency (IAEA) said. Tehran’s move has escalated international tensions over its nuclear program, putting it in a position to dramatically reduce the time in which it can enrich a significant amount of material to weapons grade.

Iran claims that the additional enrichment is aimed at refueling a research reactor in Tehran that operates on about 19.75 percent LEU and is expected to run out of fuel later this year. (See ACT, November 2009.)

The new IAEA report indicated that, on Feb. 14, Iran transferred about 1,950 kilograms of LEU from its commercial-scale enrichment facility at Natanz to a much smaller pilot enrichment facility at the same location in order to carry out the enrichment to 20 percent. The transferred amount represents more than 90 percent of the total estimated stockpile Iran has produced since it began large-scale enrichment in 2007.

The percentage of enrichment refers to the concentration of the fissile isotope uranium-235, the isotope appropriate for nuclear weapons or nuclear power, in the material. Nuclear power reactors typically use uranium enriched to about 4 percent. Weapons-grade enrichment levels are generally around 90 percent, although nuclear weapons can also be produced using uranium enriched to about 80 percent. The IAEA defines highly enriched uranium (HEU) as uranium enriched to levels of 20 percent and higher.

The majority of the enrichment work needed to get to weapons-grade HEU levels, however, is carried out while enriching to LEU levels. A Feb. 8 Institute for Science and International Security (ISIS) report says that “producing 3.5 percent enriched uranium is about 70 percent of the way to weapon-grade uranium in terms of enrichment efforts.” The authors say that if Iran enriched its entire stockpile of LEU to 20 percent, “it would be going most of the remaining way toward the production of weapon-grade HEU.”

Two days after Iran began its initial steps to further enrich LEU, President Mahmoud Ahmadinejad announced during a Feb. 11 public rally commemorating the 31st anniversary of the Iranian Revolution that Iran had produced its first batch of 20 percent-enriched uranium. He also boasted that Iran had the capacity to enrich to much higher levels if it desired. “We have the capability to enrich to more than 20 percent and to more than 80 percent, but because we don’t need to, we won’t do so,” he said.

Expanding on Ahmadinejad’s claim, Atomic Energy Organization of Iran (AEOI) Director Ali Akbar Salehi told Reuters Feb. 11 that Iran not only has the capability of enriching to far higher levels, but doing so “is a legal right” reflected in IAEA agreements and the nuclear Nonproliferation Treaty (NPT).

Article 4 of the NPT says the parties are entitled to “the fullest possible exchange of equipment, materials and scientific and technological information for the peaceful uses of nuclear energy.” Under Article 4, the pursuit of nuclear energy is an “inalienable right,” but it must be “in conformity with” Articles 1 and 2, which contain nonproliferation commitments for the nuclear-weapon and non-nuclear-weapon states.

The February IAEA report expressed concern, however, that Iran might be engaged in efforts to develop a nuclear warhead, which would violate its nonproliferation commitment under Article 2.

Moreover, the UN Security Council has adopted five resolutions calling on Iran to suspend all enrichment-related activities and is currently holding discussions on a potential sixth. The council has asked the IAEA to report on Iran’s compliance with this demand.

Raising Enrichment in One Cascade

The IAEA reports that only one 164-centrifuge cascade at the pilot enrichment facility is capable of enrichment to 20 percent. A cascade is a collection of centrifuges used to carry out the enrichment process.

Using that cascade, Iran began enriching about 10 kilograms of its LEU to 20 percent between Feb. 9 and 11, but started that process before agency inspectors arrived. A brief Feb. 10 IAEA report on the transfer and further enrichment of the material noted that, although the IAEA requested that Iran wait for the IAEA to adjust safeguards at the pilot facility before it began feeding LEU into the centrifuges, agency inspectors were informed when they arrived at the facility Feb. 9 that Iran had already begun doing so the previous evening “for purposes of passivation.” Passivation is a process by which small amounts of the material are introduced in the centrifuges to prepare them for enrichment.

The Feb. 18 IAEA report said that Iran provided “insufficient” time for the agency to adjust safeguards before running the centrifuges with LEU. Pierre Goldschmidt, former IAEA deputy director-general for safeguards, said in a Feb. 18 e-mail that Iran “should have waited for the agency’s green light” before starting the feed, regardless of the purpose.

Salehi said Feb. 11 that the cascade is capable of producing about 3 to 5 kilograms of 20 percent-enriched uranium each month. Because that was “already more than enough” for the research reactor’s needs of 1.5 kilograms per month, he indicated that Iran would not use more than one cascade for the additional enrichment. However, given the operating performance history of Iran’s centrifuges, the cascade is more likely to produce about 1.25 to 3 kilograms per month, the ISIS report says.

When asked by Reuters how much of Iran’s stockpile would be used to produce the fuel, Salehi replied, “[W]e will adjust it,” noting that 10 kilograms of 3.5 percent LEU produces 1 kilogram of 20 percent-enriched uranium.

At that ratio, Iran could produce about 195 kilograms of 20 percent-enriched uranium from the amount it transferred to the pilot facility. That amount would be enough to run the reactor at full capacity for more than 10 years, or about twice as long if Iran continued to operate it at lower power levels, as it has since the 1990s. Tehran has claimed that it needed 120 kilograms of the material to run the reactor.

The production of such a large amount of 20 percent-enriched uranium fuel for the Tehran reactor appears to contradict Iran’s stated intention of replacing that reactor once another research reactor under construction at Arak is completed. In 2006, AEOI’s then-director, Gholamreza Aghazadeh, told the Iranian Students News Agency, “Tehran’s reactor will be turned off by the time that Arak’s reactor is started up.”

Although initially slated for completion in 2009, the heavy-water Arak reactor is currently expected to be completed next year and begin operations in 2013. That reactor runs on natural uranium fuel, which does not need to be enriched. Iran has said it expects the process line for producing fuel for the Arak reactor to be completed this month.

The IAEA and UN Security Council have called on Iran to halt the construction of that reactor because of concerns it can be used to produce one to two bombs’ worth of plutonium each year. (See ACT, November 2006.)

In addition to having transferred an amount of LEU well in excess of what it claims to need for the Tehran reactor, Iran does not currently have the capability to convert the 20 percent-enriched uranium into the necessary fuel assemblies. According to the ISIS report, Iran could develop the means to create the fuel for the reactor, but “it would take some time to master the process” and would run quality assurance and reactor-safety risks.

The IAEA report indicated that Iran intends to install a process line at its uranium-conversion facility for research and development on producing LEU metal enriched up to 19.7 percent, presumably in preparation for fueling the reactor.

Fuel Swap Rejected?

Iran’s move to enrich LEU to 20 percent appears to rule out the possibility of reaching agreement on an IAEA proposal for Iran to swap much of its LEU stockpile for fuel for the Tehran reactor. Last October, Iran initially agreed “in principle” to a proposal under which France, Russia, and the United States would provide fuel for the reactor. Shortly thereafter, Tehran sought changes to the arrangement to provide “100 percent guarantees” it would receive the fuel, threatening to enrich to 20 percent itself if those changes were not accepted. (See ACT, December 2009.) Those changes included a simultaneous exchange of material on Iranian soil and export of the LEU in several shipments rather than all at once.

In January, after failing to respond to a Dec. 31 deadline by the West to accept the IAEA-brokered plan, Iran declared that it would proceed with enrichment to 20 percent in one month if its proposed changes were not accepted.

Both sides have said that a fuel swap is still on the table, but Iran is not willing to agree to the IAEA-brokered proposal, and the other parties have refused to accept Iran’s demands to stagger the LEU shipments or carry out a simultaneous exchange. Under the IAEA proposal, Iran would ship its LEU immediately, as a confidence-building measure, and would receive the fuel about one year later once it was manufactured.

Iran’s plan for further enrichment prompted several countries to question its motives. A Feb. 12 letter to Amano from the permanent representatives of France, Russia, and the United States to the IAEA stated that Iran’s additional enrichment was “wholly unjustified,” violated UN resolutions, and represented “a further step toward a capability to produce” HEU.

The letter also highlighted a number of provisions in the IAEA proposal, the text of which has not been made public, intended to give Iran assurances that it would receive the reactor fuel. Those assurances included placing Iran’s LEU in the formal custody of the IAEA, holding the LEU in escrow in a third country until Iran received the fuel, and making the exchange a legally binding arrangement.

Centrifuges More Efficient

As Iran prepares to increase the enrichment level of much of its LEU stock, it is continuing to increase the efficiency of the centrifuges operating at its commercial-scale plant.

Iran is currently enriching uranium in about 3,800 of the 8,600 centrifuges installed in that facility, down from about 4,000 enriching in November 2009 and a high of about 5,000 enriching last May, according to the IAEA report. In spite of the decrease in the number of operating centrifuges, its monthly LEU output remained steady at about 85 kilograms between May and November, increasing to about 113 kilograms between November and January.

The reasons behind Iran’s reduction in centrifuge operations are unclear, but experts and Western diplomats said in February that Iran has continued to face technical hurdles in consistently operating large numbers of machines.

Update: March 5, 2010

During a March 1 meeting of the IAEA Board of Governors, Iranian envoy to the agency Ali Asghar Soltanieh said that Iran had moved the vessel containing most of its LEU stockpile back from its pilot facility to its commercial-scale facility underground. The move suggests that Iran may not enrich the entire stockpile to a level of 20 percent.

Soltanieh appeared to indicate that Iran originally moved the 1,965 kilograms of LEU to the pilot facility because the material was stored in a single container vessel and moving the entire vessel was necessary to enrich any amount of the LEU further.

Iranian technicians “just moved the capsule because technically they needed it and they have put it back,” Reuters quoted Soltanieh as saying March 1. “We used the material which we needed for the Tehran Research Reactor,” he added.

IAEA officials contacted by Arms Control Today could not confirm that the move had occurred.