“MCNP SIMULATION OF A SHIELDING FOR A HYPOTETICAL PROTECTED THEFT”

There is a potential threat that individuals or groups could acquire and use nuclear material unlawfully. In order to prevent such a threat, a set of security measures should be taken. One of them is the entry and exit control of materials from nuclear facilities. In this paper, a hypothetical scenario of protected theft was broached, where an active non-violent insider with authorized access, authority and knowledge attempts to steal small quantities of highly enriched uranium (HEU) using a plastic shield. The importance of this type of study is to determine the possible weaknesses of the radiation detection system of a nuclear facility, allowing the upgrade of the system and preventing this type of malicious insider activity. A simple set-up was adopted in an initial study. A plastic shielding was simulated by using the computational Monte Carlo code MCNP - Monte Carlo N-Particle - with different thicknesses in order to find out the minimum thickness necessary to shield a small quantity of HEU from gamma radiation detectors. Preliminary results show that the tested shielding can reduce around 90% of photon flux. A reduction of around 80% of photon flux is sufficient to cover-up a malicious act. More simulations are being carried out for thicker shielding, and also other types of shielding will be studied.