Structural Analysis of an Optimally Designed Spherical Tokamak Centerpost

The realization of commercialized fusion power will involve the development of new materials that can withstand the uniquely harsh nuclear fusion environment. Of particular interest are those materials that are closest to the plasma. The combination of thermal loading, neutron damage, material sputtering, and redeposition provides uniquely hostile conditions under which no material testing has yet occurred. An experimental Fusion Nuclear Science Facility is required that will create the environment that simultaneously achieves high-energy neutrons and high ion fluence necessary in order to bridge the gaps from ITER to the realization of a fusion nuclear power plant. One concept for achieving this is a high-duty-cycle spherical tokamak (ST). The centerpost is a critical component of the ST design, as it controls the size of the entire reactor. The centerpost will experience significant thermal loading and thermal gradients from ohmic heating, nuclear heating, and water cooling. Nuclear heating will also produce embrittlement and swelling in the centerpost. In addition to thermal loads, the centerpost must be designed to carry mechanical loads produced from the various magnetic fields (TF, PF, and plasma currents), both steady state and transient. The centerpost temperature must remain low enough to permit water cooling, and stresses must remain low enough so that the centerpost remains structurally sound. This study will focus on the stress analysis of a centerpost optimized to reduce the thermal gradients in the cross section.