Investigation of Irradiation Position and Target Thickness Effect on Self-Shielding Phenomena and the Product Specific Yield of 60Co and 131I in TRR

The most important application of research reactors is the radioisotope production. Certain target nuclei exhibit a high neutron cross section and strong resonances, resulting in a phenomenon known as self-shielding. Computational calculations can significantly aid in determining the optimal irradiation position for any target to maximize product yield, specific yield, and minimize negative effects during the routine operation of a nuclear reactor. This study aims to investigate the irradiation of TeO2 and cobalt metal targets in the Tehran research reactor at different irradiation positions. The simulation results indicate that for TeO2 targets, there is no significant dependence of the self-shielding phenomenon on target thickness. It is evident that selecting internal irradiation boxes can enhance the yield of the 131I by a factor of 2 to 3, due to the increased neutron flux within the central irradiation boxes of the reactor core. Conversely, for 60Co, a central irradiation unit could not be employed to achieve kilocurie activity because of the substantial negative reactivity it introduced into the TRR core.