Title: In-Vessel Melt Retention (IVMR) Analysis of a VVER-1000 NPP
Publisher: Publications Office of the European Union
Publication Year: 2016
JRC N°: JRC101823
ISBN: 978-92-79-58898-3 (print)
978-92-79-58899-0 (PDF)
ISSN: 1018-5593 (print)
1831-9424 (online)
Other Identifiers: EUR 27951
OP LD-NA-27951-EN-C (print)
OP LD-NA-27951-EN-N (online)
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC101823
DOI: 10.2790/438713
Type: EUR - Scientific and Technical Research Reports
Abstract: As part of the outcome of the EU “Stress Tests” in 2012, several areas for further research in the field of Severe Accident Management have been identified for different types of NPPs. One of these areas concerns the feasibility of In Vessel Melt Retention (IVMR) for VVER 1000 reactors. Ensuring that the corium could stay in the RPV (like it happened during the TMI-2 accident) during a Severe Accident would reduce significantly the loads on the last barrier (the containment) and therefore reduce the risk of release of Fission Products to the environment for most of the Severe Accident Scenarios. This type of Severe Accident Management strategy has already been incorporated in the SAMGs of several operating small size Light Water Reactors (reactor below 500 MWe (like VVER440)) and is part of the SAMG strategies for some Gen III+ PWRs like the AP1000. Starting from 2012, several research institutes and utilities in Europe (and also in the Russian Federation) started some work on this topic. The preliminary results of these first investigations highlighted that large uncertainties (especially in the area of modelling activities) were existing regarding IVMR for VVER1000. This highlighted the need to start an activity supporting the assessment of these uncertainties and one way envisaged was to set up an international benchmark on computer code calculations for “In Vessel Retention for VVER 1000”. JRC-IET was asked by UJV Rez a.s to organize this international benchmark on computer code calculations for “In Vessel Retention for VVER 1000” with the target of providing preliminary results on the feasibility of this mitigation strategy in case of severe accident for such kind of plants. This benchmark attracted right from the beginning the interest of many EU and non EU partners. Kurchatov Institute provided freely to all partners the necessary data (ASTEC dataset, Severe Accident initial conditions, etc…) to start their own calculations, and to benchmark them with the one already performed at KI. In the meantime the interested for this topic has continued to grow and several other EU institutions joined this benchmark especially because the subject of IVMR is also applicable for other types of NPPs, expanding the work as initially planned. A larger project on the topic was prepared in 2014 and proposed to the H2020 call NFRP-01-2014: “Improved safety design and operation of fission reactors”, in order to expand the level of knowledge reached so far. The report is broken down into seven main Chapters and three appendixes. • Chapter 1 provides background information for this activity and expected results defined by the participants; • Chapter 2 provides a general description of In-Vessel Melt Retention (IVMR) principle; • Chapter 3 provides a short description of the VVER-1000 and VVER-440 design, focussing especially on those details regarding IVMR. It includes general pictures and a detailed picture of the VVER-1000 Lower Head (metallic structure, core barrel, etc…); • Chapter 4 describes the existing calculations carried out mainly by KI that constituted a starting point of this benchmark, including useful references; • Chapter 5 is the core of this report, explaining how the calculations were carried out, analysing and comparing the results. Two kinds of codes were used: CFD (CFX, NEPTUNE CFD, RELAP- 3D) and mechanistic / lumped parameters codes (ASTEC, SOCRAT, MAAP, PROCOR, MELCOR); • Chapter 6 presents existing approaches of IVMR for AP1000 and other NPPs to demonstrate its applicability and summarizes past experiments on the topic; • Chapter 7 summarizes the findings identified in the benchmark and discusses the remaining open issues; • Appendixes collect individual calculation reports, first round of calculations, and a description of main models used by every code.
JRC Directorate:Nuclear Safety and Security

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