Non proliferation issues related to misuse of research reactors

The purpose of this study is to investigate the proliferation potential of research reac- tors. These kinds of reactors present particular characteristics that make them dier- ent than commercial power reactors from a proliferation point of view. In particular, they are easily accessible and allow rapid core conguration modication to achieve high neutron uxes, as usually they are not sealed by IAEA. According to the Agency, there are three possible proliferation path ways for research reactors: diversion of fresh fuel for U235 extraction; diversion of spent fuel for plutonium extraction; clandestine plutonium production via irradiation facilities. The last is of particular interest be- cause there is no way to determine exactly which kind of experiments are taking place every moment in irradiation channels. Moreover, irradiation time can be optimized in order to achieve high quality weapon grade plutonium. With regard to the safeguard measures currently adopted, IAEA concentrates its eorts on those reactors whose thermal power is greater than 25 MW, because it was calculated that a 25 MW LEU- fuelled reactor produces about a Signicant Quantity of Pu (8 kg) per year in its spent fuel and a HEU-fuelled reactor of this power would require an annual reload of about a Signicant Quantity of U235 (25 kg)[6]. This paper investigates whether it would be possible to determine an analogous power level threshold in order to estimate the clandestine plutonium production capability of dierent research reactors. The Monte Carlo method was used to determine the neutron uxes in the irradiation channels and to calculate the plutonium breeding potential of three dierent reactor types: a Triga Mark II with 250 kWth, rapresentative of a small size research reactor; a Material Test Reactor (MTR) with 5 MWth, rapresentative of a medium size research reactor; an High Flux Reactor (HFR) with 45 MWth, rapresentative of a large size research reactor. It was observed that the most important factors for plutonium breeding are the neutron ux (to which reaction rates are proportional) and the available space for irradiation samples placement.