The relative importance of radiation heat transfer in the core of the Very High Temperature Reactor (VHTR) at full power conditions was investigated. In the VHTR with its annular core layout designed to aid radial transport of heat outward for upsets where forced convection cooling is lost, a significant temperature gradient can exist during normal operation at the interface between the inner fuel columns and the reflector columns at the core barrel. Calculations show that while the power transferred by radiation in the fueled elements at full power is very small compared to that removed by other mechanisms, in the reflectors this is not the case. Instead the magnitude is of the order of the heat removed by forced convection and the heat generated by irradiation. Accurate prediction of temperatures in the outer reflector region requires that all three phenomena be modeled.
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