Development of Surrogate Model for Prediction of Corium Debris Agglomeration - 14366

Ex-vessel severe accident mitigation strategy in Nordic type Boiling Water Reactors (BWRs) imply that melt released into a deep pool of water below reactor vessel will form a coolable by natural circulation porous debris bed. However, if liquid melt is not completely fragmented and quenched when it reaches the bottom of the pool it can cause agglomeration of debris, increasing hydraulic resistance and thus worsening coolability of the bed. In the previous work we have developed and validated an approach to prediction of mass fractions of agglomerated debris using Fuel-Coolant Interaction (FCI) code VAPEX-P. This paper discusses development of a surrogate model (SM) which can predict fraction of agglomerated debris with high computational efficiency. Such model is a must for affordable sensitivity and uncertainty analysis in different accident scenarios. Details of the SM development and verification against full model are provided in the paper. (authors)