Neutronic effects of the ITER Upper Port environment update in C-model

This paper presents analysis of neutronic effects carried out with the newly developed MCNP model of the ITER Upper Port (UP) environment integrated into the neutronics C-Model of the ITER tokamak machine. C-Model includes only the standard ITER components and generic port plugs. With a number of other important updates in addition to the description of the UP environment, the new C-Model R180430 has been issued 30/04/2018, and currently is the ITER-reference model to be used in any ITER-related neutronics analysis. One of ITER's design targets is to maintain a limit of 100 mu Sv/h for Shut-Down Dose Rate (SDDR) after 12 days of cooling time in the areas of envisaged personnel access with hands-on maintenance. In case of UP, the maintenance access is planned inside of UP duct where Inter-Space Structure (ISS) will be installed. Therefore, neutronics analysis has been focused on estimations of SDDR inside the UP duct and, following the ALARA principle, on finding the UP design solutions for reduction of dose. This task has been accomplished by 3D visualization of the SDDR map at UP duct, and drawing SDDR isosurfaces which revealed areas of dose hot spots and the radiation streaming pathways. Such information allows an understanding of the weak areas of the UP shielding and the formulation of the means for potential improvement of the radiation conditions in the UP duct area. The R2Smesh code has been used in SDDR calculations, with capability to plot distributions of decay gamma sources and revealing which radioactive materials are dominant contributors to SDDR. Comparison with the previous version of the ITER generic model called C-lite V2R150304MOD shows that the newly created C-Model R180430 demonstrated similar SDDR at the UP ISS maintenance corridors.