C.7. Hydrodynamic experiments
47. One necessary step in a nuclear weapon development programme is determining whether a theoretical design of an implosion device, the behaviour of which can be studied through computersimulations, will work in practice. To that end, high explosive tests referred to as “hydrodynamic experiments” are conducted in which fissile and nuclear components may be replaced with surrogate materials.41
48. Information which the Agency has been provided by Member States, some of which the Agency has been able to examine directly, indicates that Iran has manufactured simulated nuclear explosive components using high density materials such as tungsten. These components were said to have incorporated small central cavities suitable for the insertion of capsules such as those described in SectionC.9 below. The end use of such components remains unclear, although they can be linked to other information received by the Agency concerning experiments involving the use of high speed diagnostic equipment, including flash X ray, to monitor the symmetry of the compressive shock of the simulated coreof a nuclear device.
49. Other information which the Agency has been provided by Member States indicates that Iran constructed a large explosives containment vessel in which to conduct hydrodynamic experiments. The explosives vessel, or chamber, is said to have been put in place at Parchin in 2000. A building was constructed at that time around a large cylindrical object at a location at the Parchin military complex. A large earth berm was subsequently constructed between the building containing the cylinder and a neighbouring building, indicating the probable use of high explosives in the chamber. The Agency has obtained commercial satellite images that are consistent with this information. From independent evidence, including a publication by the foreign expert referred to in paragraph 44 above, the Agency hasbeen able to confirm the date of construction of the cylinder and some of its design features (such as its dimensions), and that it was designed to contain the detonation of up to 70 kilograms of high explosives, which would be suitable for carrying out the type of experiments described in paragraph 43 above.
50. As a result of information the Agency obtained from a Member State in the early 2000s alleging that Iran was conducting high explosive testing, possibly in association with nuclear materials, at the Parchin military complex, the Agency was permitted by Iran to visit the site twice in 2005. From satellite imagery available at that time, the Agency identified a number of areas of interest, none of which,however, included the location now believed to contain the building which houses the explosives chamber mentioned above; consequently, the Agency’s visits did not uncover anything of relevance.
51. Hydrodynamic experiments such as those described above, which involve high explosives inconjunction with nuclear material or nuclear material surrogates, are strong indicators of possible weapon development. In addition, the use of surrogate material, and/or confinement provided by a chamber of the type indicated above, could be used to prevent contamination of the site with nuclear material. It remainsfor Iran to explain the rationale behind these activities.
C.8. Modelling and calculations
52. Information provided to the Agency by two Member States relating to modelling studies alleged to have been conducted in 2008 and 2009 by Iran is of particular concern to the Agency. According to that information, the studies involved the modelling of spherical geometries, consisting of components of thecore of an HEU nuclear device subjected to shock compression, for their neutronic behaviour at highdensity, and a determination of the subsequent nuclear explosive yield. The information also identifies models said to have been used in those studies and the results of these calculations, which the Agency hasseen. The application of such studies to anything other than a nuclear explosive is unclear to the Agency.It is therefore essential that Iran engage with the Agency and provide an explanation.
53. The Agency obtained information in 2005 from a Member State indicating that, in 1997, representatives from Iran had met with officials from an institute in a nuclear-weapon State to requesttraining courses in the fields of neutron cross section calculations using computer codes employing MonteCarlo methodology, and shock wave interactions with metals. In a letter dated 14 May 2008, Iran advised the Agency that there was nothing to support this information. The Agency has also been provided with information by a Member State indicating that, in 2005, arrangements were made in Iran for setting upprojects within SADAT centres (see Section C.1 and Attachment 1), inter alia, to establish a databank for“equation of state” information42 and a hydrodynamics calculation centre. The Agency has also been provided with information from a different Member State that, in 2005, a senior official in SADAT solicited assistance from Shahid Behesti University in connection with complex calculations relating tothe state of criticality of a solid sphere of uranium being compressed by high explosives.
54. Research by the Agency into scientific literature published over the past decade has revealed that Iranian workers, in particular groups of researchers at Shahid Behesti University and Amir Kabir University, have published papers relating to the generation, measurement and modelling of neutrontransport.43 The Agency has also found, through open source research, other Iranian publications which relate to the application of detonation shock dynamics to the modelling of detonation in high explosives,and the use of hydrodynamic codes in the modelling of jet formation with shaped (hollow) charges. Such studies are commonly used in reactor physics or conventional ordnance research44, but also have applications in the development of nuclear explosives.