Plant application of ICARE/ASTECv2.0r3 computer code for investigation of in-vessel melt retention in VVER-1000 reactor design R. Gencheva ⇑ , A. Stefanova, P. Groudev Institute for Nuclear Research and Nuclear Energy (INRNE), Tzarigradsko shaussee 72, 1784 Sofia, Bulgaria article info Article history: Received 14 August 2014 Received in revised form 17 February 2015 Accepted 20 February 2015 Available online 11 March 2015 Keywords: In-vessel melt retention VVER1000 Corium Severe accident computer codes Stand-alone calculation abstract This investigation was done to assess the applicability of the In-Vessel Melt Retention (IVMR) strategy with external vessel water cooling for the reactors of VVER-1000/320 type. The IVMR strategy has been studied in different countries and the existing knowledge can assess the applicability of the strategy for VVER-1000/320 reactors and to identify the main remaining issues. IVMR strategy is one of the feasible solutions to mitigate severe accidents of VVER-1000/320 reactors but it needs to be further developed and optimized. The analytical work aimed at further identification and verification of conditions for successful IVMR application. The results achieved with severe accident computer codes like ASTEC could predict these conditions. The priority issues evaluated in this paper are the heat transfer from the corium to the reactor pressure vessel (RPV) and the heat transfer from the RPV to water outside the vessel. ICARE/ASTECv2.0r3 computer code was used to predict the heat fluxes from the corium to the vessel and the heat fluxes from the vessel to the outside coolant. It highlighted key periods of maximum heat input to the vessel steel wall that the steel wall has to be capable of sustaining. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction In this paper in-vessel melt retention investigations are presented with external vessel water cooling in case of severe accident. During a severe accident a large quantity of molten core material may relocate to the lower plenum of the reactor pressure vessel, where it starts to interact with the stainless steel of the ves- sel. This causes heat up of the lower head vessel and its eventual failure. In-vessel melt retention strategy through external cooling of the reactor vessel is one of the essential Severe Accident Management (SAM) measures at nuclear power plants. The aim is to terminate the progress of a core melt accident and to ensure the final coolability of the reactor pressure vessel. The IVMR con- cept was proposed for the first time by Theofanous et al. (1996). For the VVER design it was investigated in detail for the Loviisa VVER-440 type reactor in Finland via bench-marking with severe accident computer codes (Kymäläinen et al., 1997). ASTEC computer code (Allelein et al., 2003, 2005) was devel- oped by IRSN (France) and GRS (Germany) to be a European com- putational tool for simulation of severe accidents in the different reactor designs. Significant attention was paid on the applicability of ASTEC (Chatelard et al., 2014; Matejovic et al., 2014) to the VVER reactor types. Studies with ASTEC on IVMR as a severe accident mitigation strategy for the VVER reactors were initiated a few years ago in the frame of SARNET and SARNET2. An assessment of the code applicability was done using the results from experiments like LIVE L1, L4 and L6 (Buck et al., 2010; Palagin et al., 2012). Benchmarking with other codes was also used as a tool for ASTEC code assessment (Tarabelli et al., 2009). This paper aims to re-establish the focus on VVER-1000 reac- tors. Using the ICARE stand-along application of ASTECv2.0r3 with adequate external boundary conditions for lower head vessel region it is possible to simulate any vessel external cooling (Zvonarev et al., 2014). The investigation hereafter concerns a stand-alone calculation performed with ICARE/ASTECv2.0r3 computer code and input model for VVER-1000 reactor vessel design. In the calculation external water cooling of the vessel lower head was simulated. http://dx.doi.org/10.1016/j.anucene.2015.02.039 0306-4549/Ó 2015 Elsevier Ltd. All rights reserved. Abbreviations: ASTEC, Accident Source Term Evaluation Code; HF, heat flux; ICARE, module of ASTEC computer code; IVMR, in-vessel melt retention; NPP, nuclear power plant; RPV, reactor pressure vessel; SAM, Severe Accident Management; SBO, station blackout; VVER1000, water–water energy reactor. ⇑ Corresponding author. Tel.: +359 29795583; fax: +359 29753619. E-mail address: roseh@mail.bg (R. Gencheva). Annals of Nuclear Energy 81 (2015) 207–212 Contents lists available at ScienceDirect Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene