Analysis Of Adversary Attack Scenarios For Radiological Dispersal Device Assets

<u>Abstract </u> Radiological dispersal devices (RDDs) are weapons of mass disruption (WMD) known to be sought by various terrorist groups. Such RDDs appeal to terrorists because they require limited technical knowledge to build and deploy as opposed to a nuclear device. The threat posed by RDDs has led to an increased awareness of the need to develop and evaluate an exhaustive sets of attack scenarios. Of the many radioactive materials available, three that are generally found in healthcare facilities are considered the most attractive candidates for use in RDDs: Co-60 (radiosurgery devices), Cs-137 (blood irradiators) and Ir-192 (brachytherapy HDR devices). With different groups of adversaries employing different tactics, this paper formulates combinations of possible design-basis attack scenarios for the three sets of assets. Mathematical models of pathway analysis, probabilistic risk assessment (PRA) and Bayes theorem were employed to calculate the success probabilities of theft and sabotage of the assets. In order to capture the dynamic nature of the multiple asset and multiple player decision problems, game theoretic models were utilized as a form of rational decision-making process to rank the threats based on maximum expected utility. The product of probabilistic dependency of the attack scenarios and intentions of the adversaries formed the threat component of the triplet risk equation. The research conclusively weighed the probabilistic threat component with the regional susceptible determinants, human factors (nuclear security culture), and the subsequent consequences incurred by a successful detonation towards developing a quantitative approach of a Potential Facility Risk Index (PFRI). The PFRI, when converted into a qualitative scale, delivered a better clarification and linkage between understanding risk and making decisions about radiological security improvements. <u></u>