Monte Carlo modelling of the ARC Breeding Blanket with the Serpent code

The Affordable, Robust, Compact (ARC) fusion reactor, proposed by MIT, foresees the use of an innovative “liquid immersion” Breeding Blanket (BB), entirely constituted by a molten salt (FLiBe), serving all the BB functions (tritium breeder and carrier, neutron multiplier, coolant and shielding). Neutronic calculations have been carried out in the past with the Monte Carlo N-Particle (MCNP) transport code to estimate the Tritium Breeding Ratio (TBR), the power generation in the FLiBe, and the neutron flux to the magnets. In the present work the Monte Carlo Serpent code, developed at VTT, is used to evaluate the TBR and power deposited in the ARC BB, as a first step towards a comprehensive neutronic analysis of ARC with Serpent, thus including other relevant aspects such as magnet shielding and material activation. Two different models for the neutron source generated by the plasma are used, starting from a spatially uniform neutron source, and then moving to a non-uniform distribution, more representative of the actual differences in neutron source generation in the plasma core with respect to the edge. Moreover, an estimation of the uncertainty of the results, associated with the uncertainty in the nuclear data, is performed, thanks to non-intrusive Uncertainty Quantification methods like Polynomial Chaos Expansion. The results are compared with those available in the open literature, proving the applicability of the Serpent code to the neutronic analysis of liquid immersion BBs.