Coolability of heat-releasing debris bed. Part 2: Uncertainty of dryout heat flux

One-dimensional coolability problem for a flat homogeneous heat-releasing debris bed is considered, with the critical conditions for steady-state cooling characterized by the Dryout Heat Flux (DHF). DHF is determined for top-fed and bottom-fed debris beds from several two-phase models differing by the treatment of porous and interphase drag. Aleatory uncertainties due to randomness of the debris bed formation scenario and respective physical parameters (particle diameter, porosity) are quantified. The influence of ranges and distributions of input parameters on the uncertainty in the DHF are studied. Major contributors to the DHF uncertainty are identified. Influence of model uncertainty on the prediction of the lower boundary for DHF is discussed.

► Uncertainty of dryout heat flux is studied for various model and physical parameters.
► “95% safe” value of DHF is calculated from cumulative distribution functions.
► Model uncertainties have minor effect on the “safe” DHF value.
► Sobol sensitivity indices provide contributions of input parameter to DHF uncertainty.
► The major contributor to the total DHF uncertainty (up to 70%) is the particle size.