At high temperatures (greater than 2300 K), CO2 is known to dissociate to CO and O. A prototype solar collector was previously demonstrated to achieve such high temperatures, achieving 4-6 mol % CO in the product stream from an inlet stream of pure CO2. This paper describes the results of computer modeling performed to determine the flow, temperature, and reactions occurring in the prototype device. Of particular interest are the heat-transfer and reaction mechanisms involved and how much photolysis occurs in the prototype. Predictions were performed with two different computational fluid dynamic codes (Fluent and PCGC-3). The solar flux heated a zirconia rod at the throat of the device to 2625 K, which in turn heated the surrounding gas by convection. All CO formation reactions occurred in the boundary layer of the zirconia rod and just beyond the region of high solar flux. Predictions of CO concentrations exiting the reactor, performed using three reversible reactions, matched experimentally observed values.