Interdiction Modeling for Smuggled Nuclear Material

We describe a stochastic interdiction model on a transportation network consisting of two adversaries: a nuclear-material smuggler and an interdictor. The interdictor first installs radiation detectors on the network. These installations are transparent to the smuggler, and are made under an uncertain threat scenario, which specifies the smuggler’s origin and destination, the nature of the material being smuggled, the manner in which it is shielded, and the mechanism by which the smuggler will select a route. The interdictor’s goal is to minimize the probability the smuggler avoids detection. The performance of the detection equipment depends on the material being sensed, geometric attenuation, shielding, cargo and container type, background, time allotted for sensing and a number of other factors. Using a stochastic radiation transport code (MCNPX), we estimate detection probabilities for a specific set of such parameters, and inform the interdiction model with these estimates. INTRODUCTION The Department of Homeland Security (DHS) has been installing portal detectors in the US and these installations will likely continue [8]. The Second Line of Defense (SLD) program of the US Department of Energy (DOE) seeks to reduce the risk of illicit trafficking of nuclear material through international airports, seaports and border crossings. The program’s initial efforts were in Russia but have grown to include other key transit states in Eurasia. The DHS and DOE are addressing a real threat. In the early 1990s, Russia inherited roughly 600850 metric tons of highly-enriched uranium (HEU) and plutonium [9], and the nuclear ambitions of rogue nations make daily news. An International Atomic Energy Agency (IAEA) database includes over 1000 incidents of trafficking of nuclear and radioactive material from 1993-2006 [10]. 55% of these involved nuclear material and 18 involved weapons-grade uranium or plutonium. Sometimes a smuggler’s intent is difficult to discern, but according to the IAEA report, many of the thefts of material were motivated by profit and a perceived demand on the illegal market. Other smuggling attempts were apparently motivated by malicious intent. US efforts to assist the Former Soviet Union in securing nuclear material are ongoing, but by themselves, insufficient. An accurate inventory of the nuclear material that existed at the beginning of the 1990s seems impossible. SLD’s first detector installation was at Moscow’s Sheremetyevo International Airport in September 1998. The equipment’s installation was dedicated with a ribbon-cutting ceremony [4]. According to the DOE, such detector installations have two purposes: (i) to deter potential theft and smuggling of nuclear material and (ii) to detect and therefore prevent actual smuggling attempts. Importantly, considerable effort is being devoted to developing more sophisticated radiation detectors. Less attention is devoted to how to best deploy these detectors over a system-wide network to deter and interdict the smuggling of nuclear material. Well-designed deployment can significantly improve system performance, and in this paper, we describe a stochastic network interdiction model for locating radiation detectors. A key input to our interdiction model is the ability of radiation detectors to