Various processes and apparatus are discussed for an ultra-high heat flux chemical reactor. A thermal receiver and the reactor tubes are aligned to 1) absorb and re-emit radiant energy, 2) highly reflect radiant energy, and 3) any combination of these, to maintain an operational temperature of the enclosed ultra-high heat flux chemical reactor. Particles of biomass are gasified in the presence of a steam carrier gas and methane in a simultaneous steam reformation and steam biomass gasification reaction to produce reaction products that include hydrogen and carbon monoxide gas using the ultra-high heat flux thermal energy radiated from the inner wall and then into the multiple reactor tubes. The multiple reactor tubes and cavity walls of the receiver transfer energy primarily by radiation absorption and re-radiation, rather than by convection or conduction, to the reactants in the chemical reaction to drive the endothermic chemical reaction flowing in the reactor tubes.