A transient heat transfer model is developed to study the thermal performance of a high-temperature solar thermochemical reactor for metal oxide reduction. The solar reactor consists of an indirectly irradiated tubular fluidized bed contained in a solar cavity receiver. Radiative heat transfer in the cavity, modeled with the Monte Carlo ray-tracing method, is coupled to conduction in the tube and cavity walls. Incident radiation distributions from a diffuse radiative source and a high-flux solar simulator are implemented separately in the model to study the influence of incident radiation directionality on the performance of the reactor. Maximum temperature, maximum thermal stress, start-up time, energy balance, and particle reduction rate for the proposed reactor concept are calculated to inform the design and optimization of a prototype reactor.