Verification of safety engineering data describing the pebble flow in the HTR-modul

Literature on the flow of bulk goods has been reviewed and evaluated in order to establish a reliable data compilation that can be extrapolated and applied to calculating the conditions in the HTR-Modul. The evaluation shows that in the two upper third parts of the core of the HTR-Modul, coated particle flow can be expected to be a uniform movement, while in the bottom third part, particle residence times are expected to differ by up to a factor of two (fuel particles at the core periphery or in the center of the core). This prognostic assessment is supported by preliminary results of a series of HTR-Modul pebble flow experiments (ANABEK). Subsequent neutron physics analyses and thermohydraulic analyses have confirmed the safety engineering key data of the HTR-Modul design concept so far presented in the application documents for licensing. These data rely on a residence time ratio of 1:1.0. Proof is given of the reliable shutdown margin of the core and the limitation of the maximum fuel particle temperature under accident conditions to ≤ 1620 C, both for the case of the extrapolated flow behaviour and for a hypothetical case assuming still more unfavourable pebble flow conditions. (orig.)