SQuID-stellaraattorin neutroniikan simulointi Serpentillä

This thesis presents a neutron transport study in a SQuID stellarator, modeled using the Monte Carlo simulation software Serpent 2. The main focus is on the tritium breeding efficiency and coil neutron response. A workflow for generating the neutron transport geometry based on a predefined magnetic field and coil set was developed and applied. The neutron transport geometry is composed of the first wall, breeding blanket, vacuum vessel, and coils. The studied SQuID proved to have insufficient shielding for the coils, even with an additional neutron absorber present in the structure. The irradiation was strongly localized on distinct hotspots, located in regions where the coils are closest to the plasma. Without the additional shielding, coils reached local fast flux peaks of over 1.1e11 cm^-2 s^-1 and nuclear heating of approximately 3.5 kW per cubic meter, both roughly two orders of magnitude over their respective design limits of 1e9 cm^-2 s^-1 and 50 W per cubic meter. The peak fast neutron flux and nuclear heating were decreased with additional boron carbide shielding, but they were still over the limits in all simulation cases. The lowest fast flux peak achieved was 2.4e10 cm^-2 s^-1, whereas the lowest nuclear heating peak was at 680 W per cubic meter. Most of the coil volume was well below the limits, even without additional shielding. The Dual-Coolant Lithium-Lead (DCLL) blanket demonstrated better shielding than the Helium-Cooled Pebble-Bed (HCPB) blanket. The studied configuration showed tritium breeding ratios in the range 1.35 to 1.45 with full breeding blanket coverage, significantly over the design target of 1.15. Higher TBRs were observed in HCPB blankets compared to DCLL. Additionally, the HCPB blanket demonstrated better energy multiplication, with energy multiplication factors of over 1.3 compared to 1.15 with DCLL.