ARIES-ST nuclear analysis and shield design

A power plant design based on the spherical torus (ST) concept has been developed by the ARIES team. This paper documents the results of the nuclear and radiation protection analyses carried out for the ARIES-ST design. The nuclear analysis addresses the key neutronics issues, such as the neutron wall loading profile, radiation damage to structural components and their lifetimes, tritium breeding ratio (TBR), and nuclear heat loads to in-vessel components. The main theme of the shielding analysis is to develop guidance and recommendations on radiation protection for the TF magnet, in particular, the center-post. The need for an inboard shield, the selection of an optimal shield, the rationale for the shielding material choices, and the consequences of the shielding material choices on the overall design are reported herein. During the course of the ARIES-ST study, the design has been analyzed rigorously with a set of 3-D nuclear analyses to guide the developing design. The results of the assessment had a major impact on the design choices. For instance, the insufficient breeding along with other design constraints have ruled out the use of several attractive solid breeder blankets, the excessive neutron damage to the center-post provided strong incentives to shield the center-post, and the high radiation damage to the plasma facing components has limited the service lifetime of the ferritic steel (FS) structure to a few full power years. Furthermore, the high heat load to the inboard shield (400 MW, 10% of thermal power) forced the design to recover the inboard heating as high-grade heat to enhance the power balance. Also, the sensitivity of the outboard-only LiPb breeding blanket to the inboard shielding materials has limited the shielding options and excluded several high performance inboard-shielding materials. The performed analyses and results are reported and discussed in relation to the integrated design and the established top-level requirements for the ARIES power plants.