Optimal size of beryllium pebbles as a neutron multiplier − helium recoil calculations aiming for swelling reduction and new proposal of neutron multiplier for advanced high-temperature tritium breeding blanket

• The relationship between the size of beryllium and helium recoil release was studied using the PHITS code. • Within the studied diameter range (10 μm to 1 mm), a smaller beryllium particle size enhances helium recoil release. • A 10 μm beryllium sphere filled with lead is proposed as a candidate material for advanced tritium breeding blankets. The relationship between the size of the neutron multiplier (diameters ranging from 10 μm to 1 mm) and helium recoil release was studied using the PHITS code to reduce swelling actively. The results indicate that a smaller particle size enhances helium recoil release. However, smaller spheres are more affected by helium irradiation from neighboring spheres. To mitigate this effect, a 10 μm beryllium sphere filled with lead is proposed as a candidate material for advanced tritium breeding blankets designed for high-temperature operation. This lead-filled material is attractive because molten lead can remove helium from the system while improving both the tritium breeding ratio and the neutron-shielding performance of the fusion blanket.