Shielding Aspects of D-³He Fusion Power Reactors

The implications of the D-³He fuel cycle on shielding design are investigated for tokamak power reactors of the ARIES/Apollo class. The prime function of the shield is to protect the superconducting magnets against radiation. A variety of shield options is examined, and the various shields are optimized for the D-³He neutron spectrum. The results demonstrate the relative merits of the various materials as a function of the shield thickness. In the first wall/shield, low-activation structural materials (such as Tenelon, modified HT-9, silicon carbide composites, and carbon-carbon composites) were employed to reduce the radioactive inventory and increase the safety margin in case of accidents. A comparison between the different shield options based on detailed neutronics, environmental/safety, and economic assessments has led to the selection of the reference shield design. The first-wall/shield structure is made of an elementally tailored ferritic steel (MHT-9), and the thermal energy is converted through an organic coolant at 44% efficiency. The safety features of the low-activation steel shield, along with the low neutron production in the D-³He fuel cycle, enable the ARIES-III/Apollo design to achieve acceptable environmental and safety characteristics.