Analysis of Water Activation Loop at the JSI TRIGA Research Reactor

A closed­‑water activation loop will be constructed at the Jožef Stefan Institute (JSI) research reactor TRIGA Mark II that will serve as a well-defined and stable 6 MeV - 7 MeV gamma-ray source. The main focus of this work is to analyse three different designs of the main irradiation part of the water activation loop, which is located inside the radial piercing port right next to the reactor core, in order to achieve the highest overall activity that can be obtained with a closed‑water activation loop. These designs are in the following work referred as: “U-turn”, “spiral” and “snail”, representing the different complexity of the model, from a simple to an advanced shape. The results show that the most important parameter for to achieve the highest activity is the effective water volume, where most of the water activation reactions occur. The effective water volume of the “U-turn”, “spiral” and “snail” designs are 1.13 l, 0.52 l and 2.72 l respectively. It turned out that at saturation value the snail design systematically outperformed U-turn and spiral designs by more than a factor of two for the main water activated isotopes (16N, 17N and 19O). Furthermore, the effects of other parameters, e.g. reaction rate map, pressure drop, flow velocity profile, etc., are practically negligible as they do not differ significantly between the analysed designs. Based on that, the “snail” configuration was chosen as the main candidate for the irradiation part and also for the observation part, which is located inside and outside the radial piercing port, respectively.