KATANA - water activation facility at JSI TRIGA, Part I: Final design and activity calculations

Water as a primary coolant will play an important role in the performance of fusion reactors, as it causes an ionising radiation field throughout the facility after its irradiation and activation and requires improved shielding for instruments and personnel. To support ITER, the KATANA irradiation facility, which utilises a closed-water activation loop, was built, licenced and commissioned in early 2024 at the TRIGA research reactor at the Jožef Stefan Institute in Slovenia.A comprehensive overview of the KATANA irradiation facility, which serves as a well-defined and stable high-energy γ and neutron source, is given, including the final design, experimental set-up, detector systems and overall timeline. The physical characteristics of KATANA were assessed by analyses of neutron transport simulations leading to activity calculations in connection with a conventional analytical approach, without using CFD calculations. The KATANA facility demonstrated the desired operational characteristics in terms of high and stable water flow rates, leading to high activity values of the observed isotopes 16N, 17N and 19O, which is essential for minimising experimental uncertainties.The preliminary calculations provided in-depth operational knowledge and important data for the KATANA facility, forming a basis for more advanced future experiments.