Development of Scaling Approach for Prediction of Terminal Spread Thickness of Melt Poured into a Pool of Water

Abstract

Corium melt stabilization and long term cooling in a pool of water located beneath reactor vessel is adopted in several existing designs of light water reactors (LWRs) as an element in severe accident (SA) mitigation strategy. At certain conditions of melt release into the pool (e.g. large ratio of the vessel breach size to the pool depth), liquid melt can spread under water and reach a coolable configuration. Coolability of the melt is contingent on terminal spread thickness of the melt layer \delta_{sp} which defines decay heat generated per unit area of the melt surface. The thickness of the melt layer is determined by the competition between characteristic time scales of hydrodynamic melt spreading and solidification of the melt. This paper presents a modification of the scaling approach, originally proposed by Dinh et al. (2000) for prediction of the terminal melt spread thickness, to the case when liquid melt jet is poured into a pool of water and allow to spread unrestricted on a horizontal floor of the pool. Modified scaling approach takes into account mass and heat losses during to melt jet interaction with the coolant. The hydrodynamic spreading timescale is described with phenomenological approaches proposed by Huppert and Britter (1982) and Britter (1979). Proposed model is validated against PULiMS experiments (Pouring and Underwater Liquid Melt Spreading Konovalenko et al., 2012). Finally, sensitivity analysis and preliminary assessments of the uncertainties are performed for the PULiMS test conditions.BEST PAPER AWARD!QC 20131216</p