How to Find a Hidden Nuclear Facility
Iran's past covert enrichment activities—especially the revelation of Natanz in 2002 and Fordow in 2009—have raised concerns about whether other covert enrichment facilities exist in Iran today. In August 2010, then (and current) Iranian nuclear chief Ali Akbar Salehi claimed that the construction of an additional enrichment facility had started. However, operating a covert enrichment program is not an easy task. Several important decisions must be made which could have severe consequences for the program's survivability. For an external actor, there are three main tasks that would need to be undertaken in order to destroy a nuclear facility: detecting the facility, characterizing the facility and neutralizing it. Each of these tasks can be obstructed by different means.
Detecting and characterizing a nuclear facility can be done in several ways: with satellite surveillance; utilizing technologies that can detect radiation, heat concentrations, sound or vibrations associated with operating nuclear facilities; or by human intelligence (agents or informants). One method that is used by inspectors from the International Atomic Energy Agency (IAEA) is environmental sampling, that is, collecting samples of soil, air, water, vegetation or smears at the site of inspection and measure the isotopic composition between the uranium isotope U-235 (fissile material) and the isotope U-238 (non-fissionable material). In its natural form, the composition would be about 0.7:99.3. If enrichment has taken place the composition would have a relatively higher concentration of U-235. In general, the less enrichment that goes on (both in scale and time), the lesser the chances of detection. Therefore, the size of the facility is crucial in a covert enrichment operation, and the smaller the better. In order to miniaturize the covert facility, one should aim for installing as few centrifuges as possible. In order to reduce the number of enriching centrifuges to a minimum, one should seek to increase the centrifuge quality, that is, improve their effectiveness when it comes to separating the isotope U-235 from U-238. The Iranian centrifuge type called IR-2m is considered to be about three to five times more effective than the IR-1. Iran could limit the number of centrifuges necessary—and thus the size of the facility—by only installing the IR-2m in a covert facility.
The IAEA can only collect environmental samples at facilities declared by the country in question or at undeclared sites when the country is a signatory to the Additional Protocol of the Nonproliferation Treaty. As long as this is not the case, IAEA inspectors do not pose a serious risk to a country operating hidden facilities. However, external intelligence agencies could conduct similar missions. For example, prior to the alleged Israeli operation against a Syrian reactor in 2007, a special unit of the Israeli military was reportedly transported to the site of the reactor for the purpose of collecting environmental samples.
On-site sampling can be done only when specific information about a potential nuclear site exists. In most cases, however, one would need to look for a needle in the haystack (without actually knowing whether the needle exists). The most effective way to do this by environmental sampling is to use instruments that can measure the isotopic composition in air samples. Such instruments can have different detection range. In general, instruments with smaller ranges would have greater probabilities to detect enrichment activities. The problem with smaller ranges, however, is that for a large country such as Iran, a great many such instruments would be needed to measure every potential area. It is therefore a tradeoff between range and probability of detection. Moreover, topographical and metrological factors also affect such instruments' detection probability. Iran's topographical conditions, with hills and valleys, make effective air sampling difficult. Iran can therefore deduce that such methods are not likely to be undertaken by Western intelligence agencies unless specific information about a site is obtained.