Preparation of a water activation experiment at JET to support ITER

Fast neutron induced water activation will result in significant additional nuclear heating loads to cryogenic components in the ITER fusion reactor during operation, which are considered as an important issue in the ITER design. A water activation experiment has been proposed at the Joint European Torus (JET) which would enable measurements of radiation dose rates and N-16 concentrations in water, activated in the most representative fusion environment achievable, and extrapolability to ITER conditions. This paper presents a study aimed at establishing the experiment feasibility, in terms of the identification and selection of an experimental location at JET, and the definition of an experimental setup enabling accurate measurements of the quantities of interest. A suitable experimental location in JET was identified in the basement of the JET Torus Hall. The expected O-16(n, p)N-16 activation rates in the cooling water in the JET tokamak were determined through Monte Carlo particle transport calculations and the induced N-16 activity in the water was propagated to the experimental location. Subsequent calculations were performed to determine the expected detector response to N-16 gamma rays for three different JET pulse scenarios. Two scintillator gamma detectors were calibrated with standard gamma calibration sources and tested with a Cm-244/C-13 neutron source, also emitting 6.13 MeV gamma rays, corresponding to the N-16 gamma ray energy. The presented work demonstrates the feasibility of a water activation experiment at JET and provides valuable information for the experiment design.