Neutronics Design of Fusion Reactor–Based Boron Neutron Capture Therapy in ITER

A fusion reactor is known as a neutron-rich nuclear energy source. In this paper, neutrons are utilized to form an epithermal neutron irradiation field for boron neutron capture therapy (BNCT). Using the International Thermonuclear Experimental Reactor (ITER) facility, a beam shaping assembly (BSA) was designed and placed just before the biological shield. Treatments were planned to be carried out just outside the biological shield. An opening was prepared in the vacuum vessel to guide deuteron-triton neutrons to the BSA. The BSA is about 1 m in thickness, and on the outside surface of the BSA, an epithermal neutron flux of 1 × 10⁹ n/s‧cm⁻² was aimed. As a result of the design, the irradiation field successfully met the design criteria of the BSA advocated by the International Atomic Energy Agency. The BSA moderator consists of a first filter of 45-cm-thick iron and a second filter of 70-cm-radius and 40-cm-thick AlF₃. The epithermal neutron beam was available for diameters from 10 to 20 cm to cope with various sizes of tumors. Also, a titanium layer was specially introduced to remove fast neutrons just above 10 keV to reduce the fast neutron contribution. In addition, a caldera-shaped collimator was set just outside of the BSA to form a broad beam and to make the current-to-flux ratio larger than 0.7. It was shown from the present design that the performance was confirmed to be excellent compared to other BNCT facilities available at present, meaning that even deep-seated cancer treatment could be realized in the future in ITER.