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[en] VVER-1000/320 NPP units have the structural disadvantage concerning the location of channels for movement of ionization chambers of the RCP system. Chambers are located inside concrete wall around the reactor cavity compartment (GA301) and connected with non-hermetic compartment A336. Ex-vessel cooling of spreading corium is the main possibility for containment failure prevention.
[en] • In-vessel retention (IVR) is one of the possible SA mitigation strategies ⇒ already implemented in several reactors currently operating (VVER440) or under construction (AP1000, APR1400, CPR1000+…); • In Europe, the feasibility of IVR for high power reactors still needs to be demonstrated: – Uncertainties regarding corium behaviour; – Penalizing hypotheses lead to an over conservative assessment of the thermal loads. • The IVMR project was launched to “improve the methodology by reducing the degree of conservatism in order to derive more realistic safety margins”. ⇒ extensive program covering experimental faculties and integral codes, but also the possible uses of CFD. • This presentation will focus on the work performed at EDF, partly in the frame of the IVMR project, using the NEPTUNECFD software.
[en] Many R&D activities on the in-vessel safety issues have been performed at KAERI since 2012. Next 5-year R&D program at KAERI is focused on the ex-vessel debris coolability. The following R&D activities on the in-vessel safety issues will continue for a few more years: • SIMPLE calculations; • ICI nozzle failure test and analysis.
[en] The Fukushima Daichi Nuclear Accident represented a landmark in the history of Nuclear Power Safety. After that every single nuclear-field organization in the world focused on the study of scenarios that lead to core melting and hydrogen releases, and is analysing the in-vessel melt retention and ex-vessel corium cooling strategies.
[en] Objectves: More realistic estimation of consequence of melt release into Cavity/ Pedestal space in CV; • Evaluation of probability of MCCI/ CV failure under various water depth conditions.
[en] The purpose of the Technical Meeting is to provide a platform for detailed presentations and technical discussions on recent progress in R&D activities on in-vessel melt retention (IVMR) and ex-vessel corium cooling (EVCC) during severe accidents at water-cooled reactors (WCRs).
[en] PROCOR stands for PROpagation of CORium: its objective is to simulate the transient of severe accidents phenomena. – Only propagation of corium and its interactions are modeled (no Fission Products or H2 release); – A software platform composed by a kernel, a library of models, and different reactor applications; – A PROCOR application is an assembly of models of the library that use the services of the kernel; – PROCOR is composed of two parts: → a physical part (models and applications): to simulate corium propagation (deterministic part); → a statistical part (based on URANIE (CEA), Monte Carlo method): to perform studies on the physical part; – PROCOR has an associated work cycle in order to enhance the modelling
[en] Conclusions: • Corium localization is key measure in SAM; • Application of IVR or ExVC strategy to existing reactors requires extensive efforts on: Evaluation of efficiency of proposed strategy; Evaluation of feasibility within design of existing reactor. • UJV performs extensively R&D activities to investigate applicability of IVR strategy to VVER-1000/320 Temelin NPP: Analytical program; Experimental program; Designing of new systems or components. • Decision on application of any strategy at Temelin NPP has to be done at the end 2017.
[en] The corium behaviour R&D program consists of: The achievement of simulant and prototypical materials experiments to improve the knowledge of main relevant phenomena; The establishment of qualified physico-chemical properties and thermodynamical corium databases; The development and the qualification of both scenario and mechanistic codes for reactor calculations.
[en] Obtained results allow to draw the following conclusions: •Justification of In-vessel and Ex-vessel melt retention strategy was performed using HEFEST-ULR code. • The IVMR strategy due to external RPV cooling is possible for low powered VVER. • Success of IVMR strategy for VVER-1000 without any additional measures was not proved. Justification of IVR strategy for VVER-1000 requires additional research, uncertainty decreasing and revised estimations. R&D requires. • Ex-vessel melt retention strategy should be used for high powered VVER power units. Based on ex-vessel melt retention strategy core catcher was designed for AES-2006 and VVER-TOI projects with VVER-1200.