Nuclear analyses in support of ITER ex-port Radial Neutron Camera design

The Radial Neutron Camera (RNC) is a diagnostic system located in the ITER Equatorial Port 1 (EP01) composed by two sub-systems (i.e.: in-port and ex-port RNC) probing a poloidal section of the plasma through a set of fan-shaped Lines of Sight (LOS). The RNC is designed to provide a time resolved measurement of the neutron and alpha particles source profiles and of the total neutron source strength, through the application of reconstruction techniques to the line-integrated neutron fluxes. The Ex-port sub-system is composed by 16 LOS distributed in two different toroidal planes and enclosed in a massive shielding unit, extending from the EP01 closure plate through the Port Interspace, up to the Bioshield Plug. Neutrons, generated in the plasma core, stream through dedicated optical paths hollowed out in the central EP01 diagnostic shielding module and reach the detectors units located at the end of collimating structures. Each detector unit contains one 4He gas scintillator, one plastic scintillator as well as one single Crystal Diamond (sCD) matrix. The performed nuclear analysis allowed the selection of the SWX-277Z-5 castable borated hydrogenated mix as suitable material for the RNC shielding block; moreover, the evaluation of the nuclear heating on the ex-port RNC subcomponents, provided as input for structural analyses, highlighted that the impact of the radiation streaming is negligible with respect to the environmental thermal loads.