Measurements of Thermal and Epithermal Neutron Spatial Distribution Using Activation Foils Inside a Fusion Blanket Mock-Up

Measurement of thermal and epithermal neutron spatial distribution inside the fusion breeding blanket is essential for evaluating tritium breeding performance. This work aims to establish the method to measure thermal and epithermal neutron fluxes in the breeding blanket by employing a combination of different material foils and utilizing the differences between the various ( $n$ , $\gamma$ ) reaction cross sections. Material foils were installed inside blanket mock-ups composed of polyethylene graphite and were subsequently activated by neutron irradiation generated by deuterium–deuterium (DD) fusion reactions. Activation analyses were performed and compared with simulated results obtained by both neutron transport and activation analysis codes. Material foils were activated by neutron irradiation with an average neutron production rate (NPR) of 1.22– $1.31\times 10^{7}$ n/s for multiple irradiation experiments. The $\beta $ - and $\gamma $ -rays emitted during each decay process were measured on an imaging plate of 2-D radiation dosimeters. The detection range at measured positions was between $2\times 10^{-3}$ and $5\times 10^{-2}$ cm2/n, and calculation-to-experimental (C/E) values were 0.27–2.4 for the graphite mock-up and 0.30–3.0 for the polyethylene mock-up. These results suggest that the measurement of thermal and epithermal neutron spatial distribution can be obtained in the blanket, while the accuracy of the activation analysis using the imaging plate is required to be improved for the evaluation of tritium production.