Analysis of the accuracy of residual heat removal and natural convection transients in reactor pools

Abstract

The assessment of the inaccuracy and sensitivity of simulations of natural convection in pools is of the highest importance for the nuclear industry. Therefore, in this article we qualify the uncertainty on the calculation of three dimensional spatio-temporal evolution of Raileigh-Bènard instability.This assessment is carried out through the creation of a surrogate fast model. The model is build utilizing Proper Orthogonal Decomposition and Galerkin projection. The Proper Orthogonal Decomposition allows finding the most energetic modes. Those are derived post-processing a high fidelity CFD calculation. Those modes constitute the vectors of a new, reduced, basis. In the Galerkin Projection the governing equations are written in this reduced basis.Once the model is available, we discuss the uncertainties on the determination of the amplitudes of each mode. Concretely, we consider the hypothesis of deviations that follow the normal distribution for each mode. This normal distribution is centered in the nominal value of the amplitude and have a standard deviation which amounts 5% of the amplitude.The expected results and its uncertainty are henceforth computed by Monte-Carlo method, calculating hundreds of solutions of the Initial Value Problem with the surrogate model.