Gamma and neutron dose rate measurements around the KATANA water activation loop at JSI TRIGA reactor

¹ Reactor Physics Department, Jožef Stefan Institute, Slovenia
² Faculty of Mathematics and Physics, University of Ljubljana, Slovenia

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Published online: 6 November 2025

Abstract

KATANA water activation facility, which serves as a well-defined high-energy gamma and neutron source, has been successfully constructed at JSI TRIGA reactor at the end of 2023. During the commissioning phase γ and neutron dose rate measurements were conducted around the KATANA to create a comprehensive dose rate map under steady-state reactor operation with activated water flowing throughout the circuit. Dose rates, quantified as dose rate equivalents of H*(10)/time, were measured using a certified neutron probe and two γ detectors. The peak γ dose rate observed was up to 5 mSv/h at the close vicinity of the main observation part of the circuit (Snail head), with neutron contributions markedly lower, by more than three orders of magnitude. Due to these elevated dose rates, the experimental zone within the concrete walls has been designated as a red zone, subject to stringent access restrictions. Outside the labyrinth, however, the dose rates remained below the limit of 10 μSv/h, indicating no need for additional shielding. Experimental data were furtherly compared with the computational results using a simplified convectional method excluding detailed fluid dynamics. C/E comparison showed that the gamma dose rates were underestimated by a factor of 2–5, while neutron dose rates near the source (Snail No. 1) were overestimated by a factor of 1.8. These findings highlight the complexity of water activation analysis at KATANA and the need for accurate modelling. Future work should incorporate advanced, state-of-the-art fluid activation codes and refined experimental methods to increase precision and support benchmark-quality experiments.