Conceptual design and uncertainty analysis of a typical 50 kW aqueous homogeneous reactor aimed for medical isotope production

Abstract

Production of medical isotopes such as 99Mo, 90Sr, 131I and other fission products using Aqueous Homogeneous Reactors (AHRs) offers several advantages in comparison to other methods. In this method, after about one week operation, required isotopes can be directly extracted from the solution and the remaining fuel solution will be returned to the core for the next campaign. Moreover, AHRs are inherently safe and reliable due to their large negative reactivity feedbacks. This paper demonstrates technical features and conceptual scheme of the Iranian homogeneous reactor named RAHA, which is mainly used for the production of 99Mo/99mTc. Neutronic and thermal-hydraulic characteristics of the reactor were analyzed with MCNPX-2.6 and RELAP5/Mod3.3 codes, respectively. It was assumed that the reactor is fueled by Uranyl Nitrate, and is able to remove generated heat using natural circulation. The coolant circulation velocity was obtained as 6.5 cm/s. Four different types of neutron absorbers were considered as control rod material, and BORA resin with a diameter of 1.4 cm and Stainless-Steel cladding was chosen. As a new characteristic which may improve safety of the system, the possibility of reactor startup without any external neutron source for the case of fresh fueled core was assessed. Finally, effects of the possible uncertainties on some physical and material properties of the core were investigated and sensitivity of the effective multiplication factor relative to the uncertain parameters was also extracted using Spearman's formula.