Iran’s IR-40 Reactor: A Preliminary Assessment

November 1, 2003

Weapon Program: 

  • Nuclear


Jack Boureston and Charles Mahaffey with contributions from Yana Feldman and Charles Ferguson


FirstWatch International

Author’s Preprint
This article will be published in an upcoming issue of Jane’s Intelligence
Review (JIR).
It is not for distribution or reproduction without the
authors’ permission.


Iran has admitted that it is in the final phase of designing a 40MW heavy water nuclear reactor at Arak. Officials said that the basic design of the reactor, called the IR-40, has already been completed, and work has started on a more detailed design. Construction work is due to begin in early 2004. If this is the case, past historical data on the construction of heavy water reactors suggests that the IR-40 could be completed by 2009 at the earliest. Although the Atomic Energy Organization of Iran (AEOI) has provided technical specifications of the reactor to the International Atomic Energy Agency (IAEA) for review, the international community remains deeply concerned over the intended purpose of IR-40, its possible configuration and its capabilities.

Origins of IR-40

In July 2003, Iran revealed its plans to construct the heavy water reactor. They explained that the decision was taken in the mid-1990s after several laboratory scale experiments to produce heavy water were carried out at the Esfahan Nuclear Technology Center (ENTC). The reactor is being designed and will be constructed solely by Iranian technicians. The Iranian authorities also stated that in the past they had made numerous attempts to obtain assistance to build heavy water reactors from a variety of sources.

Western official sources believe that the reactor may be based on the successful design of the 100MW Dhruva reactor that India built at Trombay in the mid-1980s (see Table 1). In 1991, India admitted that it had offered to provide Iran with a 10-15MW heavy water reactor. That deal was probably cancelled due to US pressure on India, although Indian authorities cited technical reasons for halting the transfer.

Table 1: Specifications Dhurva reactor

Name                                 Dhurva[1]

Country                             India

Location                            Bhabha Atomic Research Center

Reactor Power                 100MW

Fuel                                    Natural Uranium

Weight of Fuel                   6.6 T

Core Size                            H: 3.87 m
                                             D: X 3.72

Max. Neutron Flux             1.8 X 10.0E +14

Moderator                           Heavy Water

Coolant                                Heavy Water

Pu Production Potential    30-35 kg/yr (in combination with Cirus)

Design                                  India


In 1992, China began negotiations with Iran to construct a 25-30MW heavy water reactor in Iran. According to Liu Xuehong, then Deputy Director General of the Ministry of Energy and Bureau of International Co-operation at the China National Nuclear Corporation (CNNC), that reactor would have been similar to the one which China had constructed for Algeria. In 1998, media reports citing US intelligence sources alleged that the Russian Research and Planning Institute for Power Supply Technologies (NIKIET) and the Mendeleyev University of Chemical Technology had begun negotiations with Iranian authorities to supply Iran with a 40MW heavy water reactor. However, both entities and the Russian government have denied these allegations. In 1999, the United States imposed sanctions on the above-mentioned companies and eight others for providing sensitive nuclear and missile related information to Iran.

While it is most likely that none of these reactor transfers ever materialised, it is possible that at least one of the entities negotiating with Iran provided designs for a heavy water reactor, which may have given the Iranians sufficient knowledge to begin construction. Additionally, since Russia is currently contracted with Iran to build a power plant at Bushehr, it is possible that Russian scientists working on the Bushehr project may be advising Iranian engineers on the design of IR-40. Also possible is that Iran has used its Chinese-supplied zero power heavy water reactor located at ENTC as a model to design the IR-40, perhaps with Chinese technical advice. Determining the origin of IR-40 will remain difficult until the reactor’s designs are finally revealed.

Potential Configuration

To meet their isotope production requirements, the Iranian authorities decided that the heavy water reactor would need to have a neutron flux of 1,013-1,014n/cm2/s. To do so, it would need to produce approximately 30-40MW when using UO2 fuel. IR-40 is expected to produce 40MW thermal power, using a heavy water plant to supply its moderator and coolant, and will use zirconium clad UO2 elements produced at facilities in Esfahan as its fuel. The core size and configuration of IR-40 are still a mystery. However, given that IR-40 uses heavy water as a moderator, the core size may be larger due to the significant properties of heavy water. The designers must also take into account the size of the core’s surface to allow for sufficient heat transfer, moderator flow control, and the safe movement of components such as fuel elements and control rods. (See Table 2 for comparison of similar reactors).

Table 2: Selected Heavy Water-Moderated Reactors with Plutonium Production Potential

Name HWRR-II[2] Cirus[3]


Chalk River[5]


El Salam[7]









China Institute for Atomic Energy

Bhabha Atomic Research Center

Petersburg Nuclear Physics Institute

Chalk River, Ontario


Atlas Mountains

Thermal Power


40 MW


40 MW

50 MW



Natural Uranium

Natural Uranium


Natural Uranium

Natural Uranium


Weight of Fuel

Not publicly available

10.5 T

Not publicly available

Not publicly available

Not publicly available

Not publicly available

Core Size

Not publicly available

3.14m (H)

X 2.67 m (D)

Not publicly available

3.5 m

Not publicly available

Not publicly available

Max. Neutron Flux

Not publicly available

(6.7) X 13


1.1 E +07

Not publicly available



Not publicly available

Heavy Water

Heavy Water

Heavy Water

Heavy Water

Heavy Water


Not publicly available

Light Water

Heavy Water

Not publicly available



Light Water

Pu Production Potential (estimate)

3-5 kg/yr (estimate)

30-35 kg/yr (combined withh Dhurva)

15-20 kg/yr


8-10 kg/yr

3-5 kg/yr








Purpose of the Reactor

Iran has stated that the IR-40 will be used for research and development, radioisotope production, and training. One main advantage of a heavy water reactor is the low absorption factor of heavy water (D2O) over other moderators. This translates into a larger number of isotopes being produced to satisfy the increasing isotope requirements in the medical and agricultural industries.

In addition, due to the special properties of a heavy water reactor, its nuclear fuel, natural uranium (UO2), need not be enriched. Natural uranium is also better for producing plutonium, since the higher the enrichment of fissile material the less plutonium it can produce.

Proliferation Concerns

The IR-40 heavy water research reactor is significant because it produces high quality plutonium, the most important component for a compact, nuclear device. If Iran wishes to develop a nuclear weapon small enough to launch on top of its Shahab 3 or 4 missiles, it will most probably be an implosion device with a plutonium (Pu) core.  The only way to acquire that is through reprocessing irradiated fuel. Bushehr is a light water reactor that has received much international attention and most probably will continue to be closely scrutinised, making it difficult to clandestinely remove its spent fuel for reprocessing. Even if the IR-40 has just as much attention, the Iranians would have a better chance of removing irradiated fuel or irradiating natural uranium targets for Pu production in this reactor.

Indeed, a heavy water reactor is among the most dangerous in existence from a proliferation perspective.  One reason is that the low neutron cross section of heavy water facilitates a high number of U238 (uranium-238 isotope) atoms to absorb neutrons, resulting in the production of a greater quantity and better quality of plutonium product.

According to David Albright, Director of the Institute for Science and International Security, the IR-40 will be able to produce 8-10kg of plutonium per year – approximately one to two bombs’ worth of nuclear material.[8] The IAEA holds that 8kg of plutonium constitutes a “significant quantity” – enough to build a nuclear weapon.

However, such estimates of yield assume that the IR-40 will be running at full power throughout the year and the total amount of spent fuel will be used for plutonium production. Also, such estimates of plutonium yield may not be applicable unless the Iranians construct a plutonium separation (reprocessing) facility of sufficient size and capacity to support a plutonium-based weapons program. That facility, if properly designed, might also accommodate the irradiated fuel from the Bushehr reactor, should Iran decide not to return it to Russia. So far, the Iranians are only believed to have experimented with these processes on a laboratory scale at the Tehran Nuclear Research Center (TNRC) in the 1970s. If Iran were planning to go down this path, there would likely be another facility under construction somewhere in the country, presumably close to the reactor’s location.

It is also possible that the Iranians could separate the spent fuel from IR-40 and clandestinely hide portions of separated plutonium for use in a weapon at a later date. In this case, it would take longer to finally get to a “significant quantity” of plutonium. Either way, this reactor is a cause for concern, given the fact that similar reactors have been used to produce plutonium in other countries in the past; Israel and India used reactors of comparable design to the IR-40 that were capable of generating similar levels of thermal power to produce their first fission bombs (See Table 3).

Table 3: Plutonium Production Reactors of India and Israel

Name                            Cirus                                                    Dimona

Country                        India                                                     Israel

Location        Bhabha Atomic Research Center                       Negev Desert        

Thermal Power         40 MW                                         26 MW, later upgraded to 70 MW,                                                                                   and then upgraded again to up to 100-150MW

Fuel                    Natural Uranium                                         Natural Uranium

Weight of Fuel   3.14m (H) X 2.67 m (D)                           Not publicly available

Core Size                 (6.7) X 13                                           Not publicly available

Max. Neutron Flux     Not publicly available                     Not publicly available

Moderator              Heavy Water                                           Heavy Water

Coolant                    Light Water                                           Heavy Water

Pu Production Potential (est)    30-35 kg/yr                      Between 15                                                                                               and 40-60 kg/year

Design                 Canada                                                            France

Jack Boureston is Managing Director and senior research analyst at FirstWatch International (FWI), a private WMD proliferation research group in Monterey, California ( Yana Fieldman and Charles Mahaffey are research analysts at FWI. Charles D Ferguson is a scientist-in-residence based in the Washington DC, office of the Monterey Institute’s 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 or you may call/fax us at +1-831-372-5319. 

[1] Bhahba Atomic Research Centre, Dhurva,
[2] Research Reactor Database (RRDB),
[3] Bhahba Atomic Research Centre, Cirus,
[4] Research Reactor Database (RRDB),
[5] Argonne National Laboratory,
[6] Federation of American Scientists, WMD Around the World, Pakistan, Khusab,
[7] Global Security, Algeria Special Weapons,
[8] David Albright & Corey Hinderstein, “Iran, Player or Rogue,” Bulletin of the Atomic Scientists, September/October 2003.