Optimization of Target Irradiation

While 177Lu is of increasing importance in nuclear medicine, its production process requires highly expensive target material. Recovering target material in a closed-loop cycle is a common optimization of the physical production process. However, the optimal irradiation and recovery conditions for the production of 177Lu are unexplored in available literature. Some reference works address a similar optimization problem for another nuclide (238Pu). Using simulation software for the irradiation process is accurate, however no strict optimization has been performed. The main objective for this thesis, is to formulate a generalizable methodology for this optimization problem and apply it to study the optimal production of 177Lu. The irradiation and decay process is simulated using ALEPH2 and assumed to be a black-box model. Relevant input variables (as identified by other literature) are parametrized. This includes the irradiation and cooling time, as well as a parametrization of the neutron flux based on the BR2 reactor. This is used to formalize a mathematical optimization problem, for both the open-loop process and the closed-loop process, where target material is recovered from the output at each cycle. Simulations of the open- and closed-loop production processes establish basic insights into the optimal irradiation conditions and their effect on the product quantity and quality. The optimization algorithms COBYLA and MADS are proposed to solve the open-loop optimization problem. The closed-loop optimization problem is shown to ideally only use recovered material and can be optimized by considering each open-loop cycle independently in series. A qualitative study is done on the effect of perturbations in the target chemical composition and irradiation conditions on the end-product quantity and quality. Furthermore, a sensitivity analysis is conducted on the highest possible quantity of end-product – which is of sufficiently high quality.