In the November 2011 IAEA Safeguards report on Iran, the IAEA disclosed that information from member states indicated that Iran constructed a large explosives containment vessel or chamber at the Parchin military complex in 2000 to conduct high explosive and hydrodynamic experiments related to the development of nuclear weapons. After constructing the chamber at the Parchin site, some 30 kilometers southeast of Tehran, Iran constructed a building around the large cylindrical object. According to the report, “a large earth berm was subsequently constructed between the building containing the cylinder and a neighboring building, indicating the probable use of high explosives in the chamber.” The IAEA obtained satellite images showing this chamber before the roof was placed on the building.
The large Parchin complex is dedicated to research, development, and production of ammunition, rockets, and high explosives. The complex is owned by Iran’s Defense Industries Organization, and has hundreds of buildings and test sites. It is a logical site to conduct high explosive work related to nuclear weapons development, which can be hidden among the conventional high explosive activities. This strategy has been pursued by other proliferant states seeking to hide nuclear weapons development work.
ISIS has closely monitored satellite imagery of the building, as Iran apparently engaged in clean-up activities at the site in multiple phases of activity. The IAEA continues to call on Iran to grant inspectors access to the site, although as of the spring of 2013, Iran had refused IAEA access while continuing to reconstruct the site.
The IAEA has provided partial information on the type of tests that Iran may have conducted and the media have reported on additional possibilities. As best as can be determined, three types of tests could have been conducted, each with appropriate diagnostic equipment, although the IAEA has never confirmed such a list and still other types of tests are possible. The three most commonly discussed tests have been:
- A test of the spherical symmetry of the initiation of the high explosive components of a nuclear warhead, which could have involved up to 70 kg of high explosives. This test would not involve any uranium. The November 2011 safeguards report noted that the explosive chamber at Parchin would be suitable for carrying out this type of test.
- A test to ascertain the symmetry of an imploding hemispherical shell of high explosives, surrounding a natural uranium metal hemisphere, in a scaled down experiment of an implosion package. A technical advisor to ISIS with decades of involvement in the experimental study of nuclear weapon mock-up explosions evaluated this case. He assessed that based on the constraints of this chamber and the use of powerful high explosives, the explosive shell would contain about 50 kilograms of high explosives, an amount within the constraints of the chamber.
- A test of a uranium deuteride neutron initiator. Such an initiator, which is difficult to develop, must be adequately compressed by high explosives in order to produce a small burst of neutrons which initiate the chain reaction and the nuclear explosion. In a test that could have occurred in the explosive chamber, the initiator would be located at the center of a high explosive compression system involving a sphere of high explosives and possibly a non-nuclear surrogate material for the weapon-grade uranium core. The goal of the experiment is to compress the initiator, causing the fusion of the deuterium and a spurt of neutrons that could be measured by highly sensitive detectors located outside the chamber. This test would involve only a few grams of uranium and deuterium with variable amounts of explosives.
This more recent case is not the first time Parchin has aroused suspicions of secret nuclear weapons work. The site first surfaced publicly in August 2004 when ISIS was alerted by ABC News to allegations that the complex was being used for high explosives testing that may be consistent with those conducted for nuclear weapons research. Commercial satellite imagery of this collection of potential high explosive test bunkers and buildings was released publicly by ISIS in September 2004.
Within the larger Parchin complex, there is an isolated, separately secured site at which it was believed the weapons-related research could have taken place. Prior to public release of the imagery, the IAEA was aware of the facility through analysis of commercial satellite imagery and its potential for nuclear weapons-related work. Iran initially rebuffed IAEA requests to inspect the site, eventually allowing access to parts of the facility in early 2005.
On November 1, 2005 Agency inspectors were given access to a subset of the buildings at Parchin and were able to take several environmental samples. The IAEA’s February 2006 report notes that “The Agency did not observe any unusual activities in the buildings visited, and the results of the analysis of environmental samples did not indicate the presence of nuclear material at those locations.” On the ground inspections showed that certain sites were not as capable as suggested by satellite imagery. Nonetheless, the IAEA was unable to visit all the sites it wanted to inspect and the issue about nuclear weapons related work at Parchin remained unsettled.
At the time, the IAEA did not know about the high explosive test chamber mentioned above, which is located in another section of the Parchin site. The buildings it wanted to visit in 2005 are far from this chamber. Moreover, the inspectors were unlikely to have asked to visit the building housing the chamber, given its non-descript nature in a complex routinely testing high explosives and the large number of buildings at the Parchin site.
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