Development of molten jet quench model for shallow pool based on PULiMS-E10 test

Abstract

When a molten jet falls into a shallow pool in the containment vessel during a severe accident in a light water reactor, melt spreading is expected to occur on the floor surface with extremely complex fluid phenomena. In order to analyze such complex behavior, the authors identified important phenomena related to the melt spreading behavior based on experiments conducted under dry and wet conditions. The identified influential factors in under-water melt spreading are the heat transfer between the melt and overlying water, melt-coolant interaction caused by water confinement at the time of molten jet impingement, molten jet breakup into melt slugs, dispersion of melt slugs and cooling by water recirculating inside the partially solidified debris bed. In particular, a numerical model to treat the above-mentioned melt-coolant interaction and the subsequent chain of phenomena was developed. The model was named as "molten jet quench model" by the authors and was implemented in MSPREAD. In the developed model, the diameter of the spherical melt slugs and the radius of the floor surface region where melt continues to be slugs can be given as user inputs. Four sensitivity analysis cases were performed with varying diameter of spherical melt slugs and the radius of the floor surface region together with no quench cases based on the PULiMS-E10 test conducted by the Royal Institute of Technology in Sweden. Comparisons of the time histories of the spreading area, pool water temperature, spreading shapes, and post-test debris cross section indicate that the molten jet quench model can explain the short spreading distances, thicker solidified debris, and even higher pool water temperatures observed in PULiMS-E10.