Neutron emission from water activation: Experiments and modeling under fusion-relevant conditions at the KATANA facility

Abstract

Jožef Stefan Institute’s water activation experiment, called KATANA, was developed to procure benchmark quality experiments on the water activation process. This paper presents the optimization process of the neutron detector holder to achieve the neutron flux measurement system with the highest detection efficiency. Water is activated by the nuclear reactions on oxygen isotopes. The active oxygen and nitrogen isotopes then decay, emitting gamma rays and neutrons with different energies. The reaction ¹⁷O(n,p)¹⁷N is responsible for the emission of high-energy neutrons. In future fusion plants such as ITER, the neutron flux in the water cooling system will be high, with an estimated flux of approx $\Phi \approx 10^{13}$ n/cm${}^2$s. Therefore, adequate shielding must be considered. The design and implementation of neutron flux measurement system at the KATANA water activation facility represents a significant step towards a better understanding of water activation processes. Despite the challenges associated with water activation experiments, the first test measurements of neutron emission during the water activation process have yielded promising results. The following results will be presented: the measured half-life for the decay of ¹⁷N, activity of ¹⁷N as a function of reactor power and water flow rate. The initial results indicate the possibility of using such a facility for the measurements of the integral cross section for the ¹⁷O(n,p)¹⁷N reaction.