Neutronic analyses for the upper ports in the neutral beam cell of ITER

Neutronic analyses have been performed assessing the performance of the new radiation shielding design of the upper ports in the Neutral Beam (NB) cell of ITER. The scope of the work includes neutron and gamma spectra and nuclear heating calculations inside the port, as well as assessments of fluences, nuclear heating, and insulator radiation doses in the superconductive magnets in the vicinity of the upper port. For radiation transport calculations, the MCNP5 code has been applied with the Alite 4.1 standard 3D model of ITER, in which the inner structure of the upper port was converted from the underlying CAD (CATIA) data. The conversion has been accomplished by means of the McCad interface code. To address human safety issues, maps of shutdown dose rates have been produced using the Rigorous 2 Step (R2S) method enhanced with the mesh-tally capability. The mesh-based R2S approach couples the MCNP5 meshtallies with the radioactive inventory results calculated with the FISPACT-2007 activation code allowing automated calculations of shutdown doses including transport of decay gammas. All results satisfy the ITER radiation design requirements.