Effect of Shielding Design Margin on the Quantity of Fusion Reactor Material

In traditional shielding design, thicknesses of shieldings have been determined so that calculated shielding properties multiplied by safety factors do not exceed design limits. A shielding design margin is defined for the safety factors that are included in the estimated shielding thicknesses in the design process. Sensitivities of the shielding design margin to the fusion reactor scale and amount of material are examined for a typical fusion experimental reactor such as the International Thermonuclear Experimental Reactor (ITER). From these investigations, supposing the shielding design margin can be made smaller by up to half the typical value of 3 used in a reactor, the amount of toroidal coil, transformer coil, and other torus component materials can be reduced by 1.5, 0.7, and 0.7%, respectively. If one includes a reactor building and accessory facilities that are not affected by the shielding design margin, the whole reactor material reduction becomes 0.55%. Since reactor cost is assumed to be proportional to the amount of material, the 0.55% reduction may be worth $55 million when the estimated price of the reactor is assumed to be $10 billion.