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Description
Water activation plays a key role in fusion facilities, contributing to radiation fields, shutdown dose rates, and overall operational safety. High-energy neutrons produced during fusion reactions interact with oxygen and other elements in the coolant, generating short-lived activation products such as N-16 and N-17. These isotopes emit high-energy gamma radiation and neutrons, affecting radiation levels during operation and shortly after shutdown, and thus influencing shielding design, maintenance planning, and safety assessments.
The JET DTE3 campaign has provided valuable experimental data on neutron-induced activation in cooling water under fusion conditions. Water activation in the JET cooling circuit was measured during more than 1,500 JET pulses. Reproducing such complex experiments in smaller, controlled environments is essential for validating activation calculations and supporting detector development. In this work, three JET water activation scenarios were replicated at the KATANA water activation facility using pulses from the JSI TRIGA Mark II reactor.
The approach focuses on replicating the time-dependent neutron irradiation conditions observed in JET by using short, high-power TRIGA pulses. The KATANA facility enables controlled irradiation of water and its transport to the measurement volume. By adjusting irradiation parameters, the study aims to reproduce the water activation observed in the JET tokamak’s cooling circuit. Computational support with the KATANA activation tool was used to model the irradiation scenarios and predict activation responses for comparison with experimental results.
Although differences in neutron energy spectra between fission and fusion sources are known, the cross section for the O-17(n,p)N-17 reaction, with its threshold (Eₜᵣₑ ≈ 9 MeV), excludes the part of the spectrum where the two differ most. This allows the activation behaviour to be effectively approximated. Experimental results are compared with JET measurements and activation simulations to evaluate the extent to which the activation behaviour can be reproduced.
This work highlights the potential of research reactor facilities as flexible and cost-effective platforms for fusion neutronics studies, enabling experimental validation and supporting future fusion reactor development.
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