Neutron shielding analysis for the buildings of the Divertor Tokamak Test (DTT) experimental fusion facility

One of the key challenges identified in the European Fusion Roadmap for the development of DEMO is the management of heat exhaust and divertor thermal loads. Since the ITER divertor design may not be suitable for DEMO conditions, a dedicated facility named Divertor Tokamak Test (DTT) is being developed at ENEA Frascati to investigate alternative divertor concepts and power exhaust solutions in a DEMO-relevant environment. In its high-performance phase, DTT will generate up to 1.5x10^17 n/s at 2.45 MeV, with an additional 1% of 14.1 MeV neutrons from triton burn-up. Such neutron production makes neutronics fundamental for machine design. This thesis focuses on 3D neutronic analyses aimed at evaluating the effective dose rate outside the main penetrations of the north wall, particularly the large (2.3 m in diameter) penetration required for the NBI Transmission Line. This opening can lead to significant neutron and gamma streaming, potentially increasing occupational and public dose. The work assesses neutron and gamma streaming through the NBI penetration and evaluates several shielding options to ensure adequate protection. Transport simulations are performed with MCNP5 using advanced variance reduction techniques (weight windows generated via Global Variance Reduction) to achieve reliable results within reasonable computational times. Additionally, a nuclear heating analysis was conducted on the PF and CS bus bars to verify that streaming through basement penetrations produces negligible thermal impact compared with intrinsic Joule heating.