End-to-End Technology of Modeling a Melt-Structure Interaction During IVMR in VVER With HEFEST-URAN Toolkit

Abstract

The problem of reactor pressure vessel (RPV) integrity during in-vessel melt retention for VVER type reactor is considered. Comprehensive numerical analysis contains the modeling of full severe accident scenario including thermal and mechanical loads on the RPV. The RPV stress calculation takes into consideration vessel thermal erosion and creep with a long-term strength, and error estimations: uncertainty analysis, sensitivity study. These problems are solved with the presented HEFEST-URAN package including: HEFEST code (2D FEM analysis of melt-structure interaction), HEFEST-M code (2D FEM stress analysis) and Varia code (multivariate calculations with uncertainty/sensitivity statistical assessment). HEFEST-URAN is a subset of the SOCRAT code developed in the Russian Federation. In the paper the HEFEST-URAN methodology and validation are described with some examples. The results of multivariate calculations of IVMR for VVER-440 reactor are presented with sensitivity study of the effects of essential factors defining the RPV thermal loading and long-term strength.

Elaboration of a Phenomena Identification Ranking Table (PIRT) for the modelling of In-Vessel Retention

“…• Carénini and Fichot (2018), Filippov et al (2014) and Le Tellier et al (2015), as references of sensitivity studies; • Seiler (1999, 2000), Cho et al (2004), Lopukh et al (2000), Park et al (1999), Zhang et al (2015 for the evaluation of the parameters dealing with heat transfers; • Bechta et al (2009), Seiler et al (2007), Strizhov and Filippov (2016), Ozrin et al (2013), Fischer et al (2011) for thermochemical phenomena.…”

Main outcomes from the IVR code benchmark performed in the European IVMR project

“…The detail of these models will be discussed further in part 4.3, dealing with results obtained for case n°4. More information about code capabilities may be found in associated publications Carénini and Fichot (2016) for ASTEC, Pandazis and Weber (2018) for ATHLET-CD, Filippov et al (2010) for HEFEST_SOCRAT, Filippov et al (2014) for HEFEST_URAN, Bakouta et al (2017) for MAAP_EDF, and Le for PROCOR. The difference between the HEFEST code versions implemented in the HEFEST_URAN package and in the SOCRAT code is due to the presence of some additional models in HEFEST_URAN: enclosure radiation, in-vessel melt relocation from the core barrel, FAS-model (detailed consideration of side-wall heat flux), models of meltwater interaction, shrinkage and some other used for in-vessel and ex-vessel melt simulations.…”

“…In HEFEST-URAN simulation, at the location of the oxide crust, the heat flux to the vessel wall is drastically reduced due to the thin insulating layer introduced between the oxide and metal layers. Heat transfer from oxide to metallic layer is modelled here as an equivalent volumetric heat source in the metallic layer that is described in Filippov et al (2014). Local peaks of heat flux at both sides of the phase boundary are not obtained in realistic case and are due to the benchmark case definition with a prescribed boundary temperature instead of the vessel wall.…”