Integrity assessment of Tokamak-type fusion reactor First Wall and Blanket structures

Abstract

This study presents a nonlinear structural analysis of the First Wall & Blanket (FW/B) of the Fusion Nuclear Science Facility (FNSF), aimed at identifying potential failure modes and estimating the component’s lifetime. The analysis focuses on the accumulation of plastic strain damage and applies fracture mechanics principles to assess the effects of radiation on mechanical properties. The study uses a database for reduced activation ferritic/martensitic steel F82H, with particular emphasis on radiation-induced changes in its mechanical properties. Safety factors for various failure modes are evaluated both at the beginning of life and after neutron irradiation under normal and off-normal operating conditions. The results indicate that the most critical failure modes are flow localization, thermal creep damage, and fast fracture due to radiation-induced reduction in fracture toughness. Based on current empirical prediction methods, we estimate that the FW/B structure will likely survive for approximately one year of operation under conditions of 1.2 MW/m${}^2$ neutron wall loading and 0.25 MW/m${}^2$ surface plasma thermal flux. These findings suggest that the effects of very high fluence (100–200 dpa) may be less significant than expected, with thermal creep damage and rapid fracture toughness degradation being the primary factors controlling failure. Therefore, there is a critical need to improve creep strength at temperatures above 500 °C and to mitigate fracture toughness degradation with increasing neutron fluence. Furthermore, the development of compact fusion energy sources with neutron wall loads greater than 5 MW/m${}^2$ may require new classes of structural materials to ensure their economic viability.