Iran could produce fissile material for nuclear weapons through two methods. The first is to enrich uranium to weapons-grade enrichment levels at facilities currently under construction at Natanz and perhaps in other facilities in Iran. The second method is to reprocess spent nuclear fuel or irradiated uranium targets to separate out plutonium.
While much recent analysis has focused on Iran’s uranium enrichment capabilities, not as much is known about the potential second pathway to an Iranian nuclear bomb. To remedy that shortcoming, this assessment examines Iran’s capability to separate plutonium by investigating its past studies, experiments, and practices. It also attempts to forecast Iran’s future capabilities to produce plutonium, and consider how these may be detected.
At the outset, it is important to note that mere possession of uranium enrichment or plutonium reprocessing capabilities does not imply a nuclear weapons program. Such capabilities are necessary, but not sufficient, conditions for an indigenous nuclear weapons program. This observation highlights the continuing need for periodic inspections of a state’s nuclear capabilities.
According to Article IV of the nuclear Non-Proliferation Treaty (NPT), states in good-standing with the NPT are entitled to have access to these capabilities for a peaceful nuclear program. However, whether states that want to build an indigenous complete nuclear fuel cycle should actually be allowed to do so is open to interpretation. For example, International Atomic Energy Agency (IAEA) Director General Mohamed ElBaradei has recently raised the issue of how to provide access to peaceful nuclear technology while erecting high barriers to nuclear weapons development.
If Iran were to develop a complete nuclear fuel cycle, it would possess the potential to break out of a peaceful program into nuclear weapons production. Acquisition of reprocessing equipment and skills as well as the other components of the fuel cycle would clearly signal a latent nuclear weapons capability.
Reprocessing methods and scale of the facility
Reprocessing can employ a number of different methods to separate plutonium from spent nuclear fuel. However, all commercial scale reprocessing plants now use the PUREX process, a type of solvent extraction process, because it offers many advantages over other methods. Advantages include relatively simplified chemical engineering, involving continuous, all liquid flows of chemicals, and efficient separation of uranium and plutonium from the spent fuel. Solvent extraction processes require five essential steps, including spent fuel storage, fuel decladding and dissolution, separation of uranium and plutonium from the highly radioactive fission products contained in the spent fuel, separation of uranium from plutonium, and purification of uranium and plutonium. Mechanical methods, such as shearing, can remove or declad the spent fuel. Dissolving requires a strong acid, such as nitric acid. To separate the uranium and plutonium from the other elements of the spent fuel, PUREX uses tri-n-butyl phosphate (TBP) as solvent and odorless kerosene, or a similar chemical compound, as a diluent. Acquisition of TBP serves as a key indicator of the PUREX process. Although the PUREX technique provides efficient separation of plutonium on an industrial scale, simpler methods might offer a proliferator the means to hide a clandestine, smaller-scale reprocessing facility.
Obviously, a proliferator would not be able to hide a reprocessing facility on the scale of La Hague, where the huge French reprocessing facility is located. However, modestly sized facilities could go undetected for relatively long periods depending on access to inspectors and the frequency of inspections. The North Korean reprocessing plant built for handling the spent fuel generated by the relatively small 5 MWe (25 MWth) reactor gives a sense of scale for a small nuclear weapons program. With that reactor and reprocessing facility (a six story building 192 meters long and 27 meters wide), North Korea was able to produce about one bomb’s worth of plutonium annually.
While satellite observations using visual techniques could indicate suspect activities around small reprocessing facilities, definitively revealing reprocessing through remote sensing usually requires detecting krypton-85, a radioactive gas that is released when spent fuel is chopped up. However, the farther away from the facility, the more difficult it is to detect krypton-85 because of dissipation of the gas. On-site inspections would, of course, enable unambiguous determination of reprocessing, but obtaining this access typically demands a high level of cooperation between the IAEA and the state in question.
If a proliferator had little or no concerns about radiation safety or in meeting industry standards of plutonium extraction efficiency, a so-called “simple and quick” reprocessing plant could offer the necessary capability to separate enough plutonium for a small nuclear arsenal. In 1975, Dr. Theodore Taylor, a former U.S. weapons scientist, provided a reality check on such a plant. Before the U.S. Congress, he testified, “A commercially competitive nuclear fuel reprocessing plant … is a highly complex, sophisticated facility, costing at least several hundred million dollars. But a reprocessing facility designed only to extract plutonium for nuclear weapons could be much smaller, simpler, and less expensive. One could describe such a facility … that would require only a few months for construction and an operating crew of less than a dozen appropriately skilled people, using information that is widely published and materials and equipment that are commercially available worldwide.”
In 1977, an Oak Ridge National Laboratory report described a conceptual design for a “simple and quick” reprocessing method. Soon thereafter, the U.S. General Accounting Office (GAO) analyzed the credibility and policy implications of the report and method. The GAO assessment found that “without time constraints many non-nuclear-weapons nations have, or could acquire, the technical capability to build and operate reprocessing plants as envisioned in the Oak Ridge memorandum, and such nations could recover weapons-usable plutonium from spent nuclear fuel.” 
Experts consulted by the GAO disagreed over how quickly a nation could build such a plant. While the Oak Ridge report estimated a construction time of 4 to 6 months, other analysts pointed out that the total required time would have to factor in recruiting technical expertise, training, acquisition of equipment, and determination of a suitable site. Taking these into account, the total time span could stretch from 19 months up to 30 months. Still, most of the activity might escape detection for much, if not all, of this time. Nonetheless, the Department of Energy (DOE) assessed that “the risk of detection would begin at the time of a national decision to construct a secret plant and would involve many steps before the plutonium could be used for a nuclear explosive device.”
From the perspective of a developing nation that could tap highly-technically trained people and a relatively advanced infrastructure in certain industries, such as petroleum production, the GAO report illuminates how credible a “simple and quick” reprocessing plant would be for Iran. According to the GAO, the Oak Ridge memorandum points out that “some materials could be acquired from a small industry such as a winery, dairy, or oil refinery.” Obviously, Iran has decades of experience in the oil industry. However, many experts emphasized that this type of reprocessing facility would have a low chance of successful operation unless technically experienced people were available to run it. As discussed below, Iran over the past three decades has trained a cadre of nuclear scientists and technicians who have learned the skills needed for reprocessing.
Origins of Iranian reprocessing
Iran’s first reported experiences with reprocessing technology occurred during the late 1970s. During that time scientists had assembled a laboratory scale facility at the Amirabad, now Tehran, Nuclear Research Center (TNRC), and conducted “wet run” experiments using plain water. The research center was established at the University of Tehran in 1968 to conduct numerous experiments and to operate the TRR 5 MWth, pool type research reactor, which was supplied by the United States in 1967.
As early as the 1970s, scientists working at the TNRC apparently pursued the PUREX process because open source evidence indicates that they began to experiment with chemicals, systems, and equipment inherent to this process. For example, in 1975, A. Owlya, a staff member at the Institute of Nuclear Science and Technology, University of Tehran, reported on a study to use TBP as a diluent to extract cerium III. The study considered the purification of radiocerium using the liquid-liquid extraction method. In 1986, H. Amirian of the Esfahan Nuclear Technology Center (ENTC) reported that he researched the role of uranium concentration and free acidity in uranium mass transfer from aqueous to organic phase and vice-versa, using a pump-mix type mixer-settler with a purification capacity of 2 kg U/day for a 30% tributylphosphate/n-dodecane-uranyl nitrate-nitric acid water system. Knowledge of and experience with mixer-settler systems can help with production of key components of reprocessing plants.
After 1987, few Iranian studies were published regarding Iran’s isotope production or reprocessing research. However, in 2001 such publications re-appeared. For instance, scientists from the Amirkabir University of Technology and Jaber-Ibn-Hayan Research Laboratory (JHL) published a study on the separation of iodine-131 (I-131) from natural uranium fission product mixtures. They stated that this isotopic separation was accomplished by sorbing the I-131 on special platinum-charcoal sorbent and desorbing by buffer solution. High radiochemical and chemical purity is obtained by this method. Important parameters such as temperature, distillation rate, sorbing, and desorbing rates and I-131 separation yields have been investigated. Commercial applications of I-131 include treatment of some types of cancer. In 2002, researchers at Amir Kabir and the Atomic Energy Organization of Iran (AEOI) described the production of molybdenum-99 (Mo-99), which is a “workhorse” isotope used in nuclear medicine for diagnostic purposes. While these recent investigations did not involve plutonium separation from spent fuel or irradiated targets, the research provided additional knowledge and skills that would be necessary for developing and operating a reprocessing facility.
Revelations to the IAEA
Since the fall of the Shah and the re-emergence of Iran’s stated nuclear power program, many western officials have claimed that the underlying intent of this program was to develop a nuclear weapon. Developing a nuclear weapon would run counter to Iran’s obligations as a signatory of the NPT. The allegations pointed to Iran’s interest in both uranium enrichment and reprocessing technologies. However, Iranian officials steadfastly denied wrongdoing.
Then in October 2003 after months of new revelations regarding Iran’s nuclear program, Iranian authorities reported that their scientists had conducted experiments in plutonium separation techniques. In a letter delivered to the IAEA on October 21, 2003, Iran acknowledged that between 1988 and 1992 reprocessing-related experiments took place, irradiating a total of 7 kg of UO2 pellets, typically for two weeks at a time using the TRR reactor, in connection with a project to produce fission product isotopes of molybdenum, iodine, and xenon. According to the letter, the plutonium was separated at TNRC in three shielded glove boxes. Of the 7 kg total irradiated UO2, 3 kg was processed to separate a small amount of plutonium. The separated material was then stored at JHL. In November 2003, IAEA inspectors examined the plutonium and the irradiated targets. According to the Iranian officials, the experiments were carried out to learn about the nuclear fuel cycle, and to gain experience in reprocessing chemistry. One interviewed reprocessing expert stated that these experiments may have been measurement tools for a larger facility in the future.
Iran has received assistance in developing its reprocessing capability from several different sources. In 1967, when the United States supplied the 5 MWth TRR reactor, it also supplied Iran with hot cells and training for their use. In 1975, France may have signed a Memorandum of Understanding (MOU) with Iran to build a nuclear research center at the ENTC. In the agreement, France was to supply Iran with a research reactor and a small reprocessing facility. It is not known if any elements of this agreement were ever implemented. In the early 1990s, Iran may have also sought reprocessing related equipment from companies in Argentina, China, and Europe. In 1992, China allegedly provided, “a supply” of TBP to Iran.
Iran’s chosen method of reprocessing
As was mentioned before, open source evidence points to Iran using the PUREX reprocessing technique. The use of TBP, experimentation with mixer settlers, and studies of the solvent extraction process all point to PUREX as the preferred method. The Iranians probably chose the PUREX process for a number of reasons. First, information on the PUREX process is abundantly available in the open literature. Second, the necessary equipment can be obtained as dual-use industrial items. Third, outsiders who have helped Iran develop their reprocessing program have experience in the PUREX process. Lastly, the Iranian technicians and students that learned about reprocessing overseas may have determined that PUREX was the best route for the end product desired.
Reprocessing facility: Probable size and location
Iran’s currently known reprocessing facility is located at the TNRC, probably within the same complex of buildings as the TRR research reactor. Co-location would facilitate a relatively trouble-free transport from TRR’s irradiation chambers to hot cells that connected to the facility. Iran received some of its hot cells from the United States when it acquired the TRR reactor in 1967. Hot cells are concrete-shielded chambers with a controlled atmosphere that can be used to work safely on radioactive materials. The chamber is equipped with remote manipulators or robotic devices for this purpose.
Iran’s laboratory-scale facility can separate approximately 600 grams of plutonium per year, according to a 1977 DIA report. This amount of fissile material falls far short of what would be required for a nuclear bomb; a state would need at least four kilograms of plutonium to build a fairly sophisticated first generation weapon. As was mentioned before, between 1988 and 1992 Iran conducted numerous experiments involving the irradiation of UO2 pellets and the separation of plutonium in the three glove boxes contained in one hot cell. Later, in 1992, these glove boxes were dismantled and stored in the Esfahan Nuclear Technology Center (ENTC). However, based on relatively recently published research papers, Iranian scientists conducted experiments in which isotopes were produced and separated, implying that hot cells, or at the very least glove boxes, were still in operation after 1992.
Iran’s future reprocessing capability
Undoubtedly, based on the openly available evidence to date, Iran is currently capable, even if just at a laboratory scale, of reprocessing spent nuclear fuel and irradiated uranium targets to acquire plutonium. However, to ramp up to a nuclear weapons program, Iran would need at least a modestly-sized research reactor or reactors to create the plutonium. In addition, it would require a reprocessing facility that could handle the spent fuel generated by a reactor. Iran still does not have the reactor capacity needed to support even a modest nuclear weapons program, but it has positioned itself on the threshold of acquiring these capabilities. Also, as discussed above, Iranian technicians have developed the reprocessing-related skills, but as of yet, Iran has not shown any evidence that it has a reprocessing facility that could support a full-fledged nuclear weapons program. However, developing such a facility would only require enough time and patience in acquiring the necessary equipment. Here again, Iran appears to be on the verge of obtaining this capability.
Iran’s plutonium production sources
Two nuclear reactors capable of producing plutonium are currently operating in Iran. The largest reactor of the two, the TRR light water research reactor with 5 MW of thermal operating capacity can produce an estimated 600 grams of plutonium annually. The second reactor is the Chinese-supplied 30 kW miniature neutron source reactor (MNSR) and can only produce tiny amounts of plutonium. Both reactors are under IAEA safeguards, and presumably, future reactors in Iran would also adhere to such safeguards.
Over the years Iran has attempted to purchase and even planned to construct various power and research reactors from several different sources. However, U.S. pressure has prevented most countries from following through with any agreements made with Iran. Therefore, Iran decided to construct a reactor independent of outside assistance.
In July 2003, Iranian authorities admitted to be working on an allegedly indigenous design for a 40 MW heavy water research reactor, and they plan to start building it in early 2004 in Arak. In a subsequent letter to the IAEA in October 2003, Iran indicated that it had consulted with some foreign experts about the reactor’s design. Also in Arak, Iran has already begun construction of a heavy water production facility, which would provide the necessary coolant and moderator for the new IR-40 research reactor. When this reactor is fully operational, it will be able to produce approximately 8-10 kg of plutonium or one to two bombs’ worth of nuclear material a year.
Because the IR-40 would have roughly about one and a half times the thermal power rating of the 5 MWe (or 25 MWth) reactor that produced plutonium for North Korea, the Iranian reactor would generate about 1.5 times the spent fuel of the North Korean facility. Thus, Iran would need a reprocessing plant about the size of, or perhaps a little bigger than, the North Korean reprocessing facility as long as Iran wanted the capability of reprocessing its spent fuel about as fast as the North Koreans manipulated their spent fuel. Although open source evidence does not point to the existence of an accompanying reprocessing facility at Arak, Iran noted in a November 2003 letter to the IAEA that it had plans to construct a building with hot cells at this site. Iran stated that the purpose of the hot cells would be to produce radioisotopes. The IAEA reported in November 2003 that “Iran has agreed to submit the relevant preliminary design information with respect to that building in due course.”
In principle, the Bushehr reactor, which is due to be completed in 2005 with Russian assistance, could provide another source of spent fuel for plutonium separation although Russia has indicated that it will not send Iran fresh fuel unless the two countries reach an agreement to return all spent fuel to Russia. This light water reactor has an electric power rating of 1,000 MW and a thermal power capacity of about 3,000 MW. (Russia and Iran intend to complete at least one other reactor at Bushehr with the same power rating.) If the reactor operates at 75% of the year, which is reasonable for a commercial power plant, it could produce a least a couple of hundred kilograms of plutonium annually. However, in a mode of operation that maximized electric power generation, the Bushehr reactor would produce reactor-grade plutonium containing 60 percent or less Pu-239, which is the most desirable plutonium isotope for weapons purposes, 25 percent or more Pu-240, 10 percent or more Pu-241, and a few percent Pu-242. Pu-240 has a high spontaneous rate of fission, and the amount of Pu-240 in weapons-grade plutonium generally does not exceed 6 percent, with the remaining 93 percent Pu-239. Higher concentrations of Pu-240 can result in pre-detonation of the weapon, significantly reducing yield and reliability.
Nonetheless, in 1997, the U.S. Department of Energy warned that even reactor-grade plutonium could fuel nuclear weapons. A nation attempting to use this material for a nuclear bomb would have to surmount several engineering hurdles; however, according to the laws of nuclear physics, reactor-grade plutonium can be used to create an explosive nuclear chain reaction.
For the production of weapons-grade plutonium with lower Pu-240 concentrations, the fuel rods in a light water reactor, such as Bushehr, would have to be changed frequently, about every four months or less. Satellite monitoring and other means of detection would probably spot such abnormal operation of this reactor.
Two reprocessing pathways: A fork in the nuclear road?
Iran could try to pursue one of two reprocessing routes if it wanted to produce plutonium. Both pathways present unique challenges and limitations. First, as discussed above, within the next few years, Iran would likely have the large Bushehr nuclear power plant operating. This plant embodies the potential for dozens of nuclear weapons per year as long as Iran was willing to circumvent NPT restrictions, agreements with the IAEA, and the proposed agreement between Iran and Russia to ensure that all spent fuel from Busheher is returned to Russia. In order to handle the hundreds of tons of spent fuel, Iran would need a relatively large reprocessing facility. Iranian officials could try to justify this type of facility as legitimate within the letter of the NPT. Nonetheless, the United States and other like-minded nations would probably protest that this facility would raise too much alarm about Iran’s ability to develop a substantial nuclear arsenal.
However, if Iran had more modest nuclear weapons plans, it might travel down a second pathway by deciding to build a less conspicuous, or even a clandestine, reprocessing plant. The modestly-sized IR-40 heavy water reactor, which might be completed by the end of the decade, would produce sufficient spent fuel for plutonium separation in a small reprocessing facility. In addition, diversion of a relatively small amount of spent fuel from the Bushehr power plant could provide enough nuclear material for a handful of nuclear bombs. If Iran wanted to speed up plutonium reprocessing once it had a supply of spent fuel, it could choose a variant of this pathway, that is, the “simple and quick” reprocessing method.
While Iran has recently signaled positive intentions in opening up its nuclear program, it could continue to legitimately develop expertise and technology that would allow it to inch up to a nuclear weapons program. Therefore, keeping a close watch on the potential pathways to an Iranian nuclear bomb will continue to be important even after the IAEA has completed its initial assessment of Iran under a strengthened nuclear inspections regime.
Jack Boureston is Managing Director and senior research analyst at FirstWatch International (FWI), a private WMD proliferation research group in Monterey, California (http://www.firstwatchint.org). He has worked as a safeguards information analyst at the IAEA and researcher at the Monterey Institute’s Center for Nonproliferation Studies (CNS). Charles D Ferguson is a scientist-in-residence based in the Washington DC, office of the Center for Nonproliferation Studies.
About FirstWatch International (FWI)
FWI is a research consultancy that supports the nonproliferation efforts of government agencies, international organizations, and commercial enterprises. FWI serves its clients by conducting proliferation and WMD threat assessments. We use open sources to examine the proliferation potential of states, non-state actors, industries, and companies. More information about FWI and our past research projects can be found at our website http://www.firstwatchint.org or you may call/fax us at +1-831-372-5319.
 Mohamed ElBaradei, “Towards a Safer World,” The Economist, October 18, 2003.
 Theodore Taylor, Testimony before the House Subcommittee on International Security and Scientific Affairs, Committee on International Relations, October 28, 1975.
 U.S. General Accounting Office, “Quick and Secret Construction of Plutonium Reprocessing Plants: A Way to Nuclear Weapons Proliferation?” Report by the Comptroller General of the United States, October 6, 1978.
 Ibid, p. iv.
 Ibid, p. 2.
 Akbar Etemad, “Iran,” in A European Non-Proliferation Policy: Prospects and Problems, edited by Harald Müller (Clarendon Press, Oxford) 1987, pp. 206.
 Shyam Bhatia, Nuclear Rivals in the Middle East, (Routledge: London & New York) 1988, p.85
 Owla, A., Q. Bulletin of Facility of Science, Tehran University, (1975) v.7(1), p. 15-20.
 Amirian, H., “Application of mix-settler to study the role of uranium concentration and free acidity in uranium mass transfer, using T.B.P. as solvent,” given at National Conference on Nuclear Science and Technology, Bushehr, Iran, 14-19 March 1986.
 K. Nazari, M. Ghannadi-Maragheh, M. Shamsaii, H. Khalafi, “A new method for separation of 131I, produced by irradiation of natural uranium,” Applied Radiation and Isotopes 55 (2001) 605-608.
 Sayareh R, Maragheh, Shamsaie M., “Theoretical Calculations for the Production of Mo-99 Using Natural Uranium in Iran,” Annals of Nuclear Energy, 30 (8): 883-895, May 2003.
 David Albright, “An Iranian bomb,” Bulletin of the Atomic Scientists, January 1995.
 David Schwarzbach, “Iran’s Nuclear Program: Energy, or Weapons?” Natural Resources Defence Council, Washington, DC September 7, 1995, p. 3.
 In 1992, the western press quoted officials’ concerns about Sharif and Amir Kabir universities being used as procurement fronts. University representatives at Amir Kabir may have attempted to purchase neutron-shielding equipment, which may be used in reprocessing and research programs, from a U.S. firm, Reactor Experiments “Iran’s Nuclear Weapons Program: Iranian Procurement Fronts,” Mednews, June 8, 1992, p.6.
 Mark Hibbs, “Iran Sought Sensitive Nuclear Supplies From Argentina, China,” Nucleonics Week, September 24, 1992.
 David Schwarzbach, “Iran’s Nuclear Puzzle,” Scientific American, June 1997, pp. 62-65.
 David Albright and Corey Hinderstein, “Iran, Player or Rogue,” Bulletin of the Atomic Scientists, September/October 2003.