The retardation of the released fission products deriving from graphite structures during a hypothetical HTR-500 accident

A comprehensive computer model is presented describing the transport paths of the released fission products in the coolant gas. The transport mechanisms within the graphite are discussed in detail.An experimental assembly for the verification of the computer model is described and the measurements carried out on the retardation (retention capability) of cesium in reflector graphite are presented and compared with the calculations from the “PATRAS-CORE” program.First reliable statements under realistic conditions can be made with the example of a core heat-up accident in the HTR-500.