Neutron streaming analyses and shielding optimization through HCD openings in DTT tokamak building

The Divertor Tokamak Test facility (DTT) will be a superconductive machine that aims at studying the power exhaust issue in a DEMO relevant environment. A significant power across the separatrix (compared to the radius of the machine), PSep/R 15 MW/m is of primary importance to fulfil this requirement and it can be obtained coupling to the plasma up to 45 MW of additional power. This amount of power will be reached with a mix of Heating and Current Drive (HCD) systems: Electron Cyclotron Resonance Heating (ECRH), Ion Cyclotron Resonance Heating (ICRH) and Negative Neutral Beam Injection (NNBI). Power supply and wave generators of HCD will be hosted in remote-control buildings around the DTT Tokamak hall, and thus several ducts have been designed to connect the systems to the machine. The transmission lines will pass through dedicated holes in the main building making almost empty and big penetrations which cause a large neutron streaming through the walls. This work is devoted to a three-dimensional neutronics study, in support of the DTT licensing procedure, addressing the neutron and gamma streaming through the HCD penetrations in order to optimize and determine the effectiveness of several proposed shielding options required to protect workers, population and auxiliary systems. Neutron and gamma transport simulations were carried out with the MCNP5 Monte Carlo code. Secondary neutron and gamma sources have been used to propagate the radiation outside the penetrations. The ADVANTG hybrid transport code has been also used for variance reduction techniques in order to obtain statistically significant results in regions located several meters away from the plasma source. The results of the calculations are presented and discussed as well as the effectiveness of the proposed options to mitigate the radiation streaming and to reduce the doses outside the tokamak hall.