Neutron measurements at the KATANA water-activation loop using the neutron activation method

Abstract As the primary coolant, water is used in most current fission reactors and is also a promising coolant for future fusion devices. During normal operation, the fusion device produces plasma discharges. The primary cooling water circulates through in-vessel cooling channels and thus passes through regions of high neutron flux ( E ∼ 14 MeV ) produced by D–T fusion. During this process, cooling water can be activated and produce radioactive nuclides that emit gamma rays and neutrons (neutron energy range 0.4–1.7 MeV). Predicting the dose-rate field—the spatial and temporal distribution of radiation dose rates ( Sv ⋅ h − 1 ) produced by activated nuclides in the flowing coolant—requires coupling computational fluid dynamics (CFD) with radiation-transport and activation calculations. To validate these coupled CFD + radiation-transport + activation models and to investigate how production, transport and decay of activation products together create the observed dose-rate field, the KATANA water-activation loop at the Jožef Stefan Institute Training, Research, Isotope production, General Atomics Mark II reactor was commissioned. This paper examines the newly established KATANA water-activation loop and evaluates the feasibility of using the neutron activation method for neutron measurements at the facility. The studies show that this method can be successfully applied to detect and quantify neutrons originating from 17 N decay. Furthermore, the measurements demonstrate that this technique is capable of characterising the neutron emission rate at the KATANA water-activation loop. Finally, the paper proposes a method for estimating the neutron fluence at selected sample positions. The results encourage further use of the neutron activation method to investigate neutrons emitted by activated water. Future experiments could determine the neutron fluence-rate profile, thereby validating fluid-activation codes for ITER, DEMO and other fusion devices. This would also contribute to reducing the uncertainty of the 17 O ( n , p ) 17 N reaction cross-section.