Speaker
Description
KATANA is a water activation facility installed at the Jožef Stefan Institute TRIGA Mark II reactor in Ljubljana, Slovenia. It was developed to investigate water activation processes relevant to future fusion systems such as ITER. The primary objective of KATANA is to perform benchmark-quality experiments, e.g. the validation of the state-of-the-art fluid activation codes, for which an accurate characterisation of the neutron flux distribution in the irradiation region is essential. The neutron flux directly determines reaction rates and the resulting activity of the main radioactive isotopes (N-16, N-17, and O-19) throughout the water circuit. This work presents an experimental analysis of the neutron flux inside the inner irradiation “Snail head” of the KATANA facility, located in close proximity to the reactor core, where most of the water activation occurs.
Measurements were performed using the Libera MONACO 3 digital acquisition system and two miniature fission chambers (FC), with fissionable coatings primarily composed of U-235 and U-238. These provide sensitivity predominantly to thermal and fast neutrons, respectively. The characterisation included investigations of the detector response as a function of reactor power to establish appropriate operating regimes for counting and current modes, as well as measurements at different radial positions along the Snail head.
The measured relative radial fission rate distributions for the U-235(n,f) reaction (FC U-235) show good agreement with MCNP calculations, thereby validating both the computational model of the reactor/KATANA system and the detector performance. In contrast, significantly larger discrepancies were observed for the FC U-238: the experimental results exhibit a trend similar to that of the U-235 chamber rather than the expected U-238(n,f) response. This indicates that fast neutrons are not being detected properly, likely due to a significant contribution from thermal neutrons, and that further optimisation is required. Proposed improvements include additional coating or shielding against thermal neutrons and/or the use of a FC with ultra-high-purity U-238 coating (99.9999 %). Future work will also focus on absolute neutron flux determination through neutron activation analysis using a dedicated set of activation foils.
| Formatted abstract uploaded? | Done. |
|---|