ITER is divided into twenty sectors with three major ports per sector (equatorial, vertical, and divertor). These ports are the prevalent pathways through which neutrons can leak from the plasma region increasing nuclear responses in superconducting components inside the cryostat and activate the cryostat itself. Port shielding is a major design issue that demands accurate nuclear analysis of in-port assemblies (RF heating systems, diagnostics, test modules, etc.), prudent resolution of port shielding material compositions and proportions, and sensible arrangement of the shielding in and around the ports. Ports used for neutral beam injection and diagnostics systems also require methodical analysis of the shield disposition to mitigate the effects of plasma neutron streaming through openings and/or gaps that produce high neutron flux levels inside the cryostat. Shielding analyses were performed using the continuos energy MCNP-4A code with cross section data from FENDL-1 to determine spatial distributions of the nuclear responses inside the cryostat. Calculations were carried out using a detailed model of the reactor (all essential components) to account for radiation streaming through weakly shielded port assemblies. Emphasis was focused determining the shielding to reduce the dose rates to levels that allow hands on inside the cryostat after reactor shutdown.

The impact on the cryostat radiation environment from port-to-port "cross-talk", i.e. the effect at location near a well shielded port from radiation leaking through an open or weakly shielded port, was also investigated. Neutron flux and dose rate profiles at the cryostat were generated to identify areas where personnel access will be possible at two weeks to one month after shutdown. Preliminary results of all calculations suggest that dose rates at two weeks after the end of the Basic Performacne Phase of ITER operation will be in the range of 50 to 500 mSv/h, depending on location and port shielding effectiveness.