Analysis of ex-vessel melt jet breakup and coolability. Part 2: Uncertainty analysis

摘要

An uncertainty analysis was performed on the molten core jet breakup and cooling by assuming the ex-vessel condition in APR1400, a Korean advanced pressurized water reactor, by probabilistic framework with the Latin Hypercube Sampling (LHS) and a fuel-coolant interaction (FCI) simulation code, JASMINE, as a physics model. Eight input variables including four model parameters and four initial/boundary condition variables were chosen as uncertainty variables. Three sets of size 100 samples, in total 300 cases of inputs were produced and simulation results were obtained for each of them. Statistics of the output variables as coolability indexes: the ratio of removed heat to the enthalpy for quench and the fraction of molten pool on the floor, indicated that, in the assumed range of conditions, the debris bed is likely to be cooled in average to the solidification point by similar to 85% probability; however, it is not cooled to the minimum film boiling temperature, similar to 500 K; and, more than 1% of the melt mass is in a molten pool on the floor by similar to 65% probability. The importance analysis showed that the ratio of water pool depth and the melt jet breakup length dominates the cooling performance during the melt discharge transient. The uncertainty of initial and boundary condition variables such as the melt jet size and water pool depth is much more important than that of the model parameters. (C) 2016 Elsevier B.V. All rights reserved.