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 the construction of an additional enrichment facility had started.For external intelligence organizations, there are two main tasks that would need to be undertaken in order to a find a hidden nuclear enrichment facility: detecting the facility and characterizing it. A determined proliferator can obstruct both of these tasks with various 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 via human intelligence (agents or informants).The author is a Norwegian security analyst and a post-graduate of the MA program in security studies at Tel Aviv University.One method used by inspectors from the International Atomic Energy Agency (IAEA) is collecting environmental samples at the site of inspection and measure its isotopic composition between the uranium isotope U-235 (fissile material) and the isotope U-238 (non-fissile 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; the smaller the better. In order to miniaturize the 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 3-5 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 covert facilities.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.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 exist). 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 various detection ranges. In general, instruments with smaller ranges have a greater chance of detecting 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 site.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 organizations unless specific information about a site is obtained.A large country seeking to hide nuclear facilities would therefore concentrate on obstructing two other potential dangers: satellite imagery and human intelligence. Satellites can help answer questions regarding both detection and characterization – and even contribute to a military operation against the facility by revealing the kind of materials used in the construction process and other specifications of the facility.However, given the large size of Iran, and the somewhat limited satellite assets of most countries, searching without leads for clandestine facilities is a challenging task. Again, specific site information could be necessary. However, wide-area satellite searches are still undertaken by Western intelligence organizations.One problem for a proliferator would thus be how to deceive satellites and their operators. There are several ways to camouflage a nuclear facility. First, one can camouflage a nuclear facility by pretending it is something else. Syria attempted to conceal its reactor by constructing a fake exterior, making the building look like an old Byzantium-era fortress, of a type commonly found in Syria. Second, one can construct non-nuclear underground facilities in order to attract the attention of foreign intelligence and exhaust their resources, thus raising the probability that a real nuclear facility remains hidden.Some analysts believe that this was part of Hezbollah’s deception tactics when it in 2006 conducted two digging operations in the village of al-Hiam and near Ras Biada without attempting to hide the effort.Third, one can attempt to incorporate the facility into an existing industrial site such as an oil refinery or a milling plant, making it difficult for an outside watcher to identify non-industrial nuclear activities. This is particularly worrisome with regards to enrichment supportive activities such as uranium extraction operations and conversion into uranium gas.However, one would then have to accept a higher risk of detection from human intelligence since workers related to non-nuclear activities would also be present at the site.There is also the option of choosing a strategy for deniability in the case one is caught red-handed. The way to do this is to remove or reduce incriminating evidence before detection. This is what Iran has been doing at the Parchin site, where it has asphalted large areas of the facility so as to reduce the IAEA inspectors ´ ability to collect environmental samples.The location of the facility is also a major concern. Syria chose to locate its reactor in a desert region, hoping it would not attract the interest of foreign intelligence. One can also choose to minimize on-site security in order to reduce signatures that could alert foreign parties. On-site security includes fences, security gates, guard posts and anti-aircraft positions.The latter is of particular importance.Anti-aircraft positions are relatively easy to spot on satellite images. Therefore, using them for protection of a hidden facility would only alert foreign intelligence that something of value is located within the anti-aircraft battery’s action range.One is therefore left with two choices: either construct the facility in an area already covered by anti-aircraft batteries or avoid such defensive measures altogether.However, after exposure Iran could rapidly deploy batteries to protect it.Foreign intelligence would thus prefer to keep mum on its knowledge of an attempted hidden facility, so as not to induce the country in question to increase its on-site defensive capabilities or construct another hidden facility.Both proliferators and external intelligence organizations are faced with several dilemmas. For a proliferator, the most important ones would be to decide where the facility should be located and what defensive measures should be implemented (if any).For external intelligence agencies, the main problem would be how to use their limited assets in the most efficient way.