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[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] IVR-ERVC is selected as a Severe Accident Management Strategy for APR1400. Design Requirements: • To provide flexibility in severe accident management; • To provide an additional function for in-vessel retention by using the existing systems; • To flood the external surface of reactor vessel lower plenum before the relocation of molten corium. Implementation: • Initial flooding of the reactor vessel using a shutdowm colling pump (SCP); • Reactor insulation design for effective water intrusion and flow; • Supplementary water injection by boric acid makeup pump (BAMP) to compensate boiling-out.
[en] • In-Vessel Retention (IVR) of molten core debris via water cooling on the external surfaces of the reactor vessel is an inherent severe accident management feature of the AP1000/CAP1400 passive Nuclear Power Plants (NPPs). • Main failure modes associated with IVR: Thermal Failure / Structural Failure. • The Structural Failure assessment is also necessary because high temperature induced creep damage are the immediate threats to the RPV, especially with the sustained pressure loads existence.
[en] Model of Erosion Due to Interaction of CorIum with basement Substance: MEDICIS contains: - A model of the structure of the corium concrete interface; - Models of corium coolability in case of water injection upon the corium pool surface; - Models of evolution of corium pool configuration; - Models to evaluate the release from the ex-vessel corium pool of concrete aerosols and the release of fission products during MCCI; - interface with the physico-chemistry MDB package (Material Data Bank), to evaluate the corium layers properties.
[en] A core catcher located inside a PWR pressure vessel is designed to manage the in-vessel retention of the corium in the accidental event of the core meltdown. This solution consists of a ceramic multilayered structure, filled with alumina pebbles . The main aim of this solution is to protect the bottom head of the vessel from the heat flux caused by the Corium decay power. The cooling of the Corium can occur through the upper surface of the Corium by means of radiation and convection with a coolant flowing into the vessel. The core catcher has to contain the Corium for a time interval as large as possible. The alumina pebble bed has a low conductivity and a high loading carrying capability. A theoretical model of the thermal mechanical behaviour of pebble bed has been illustrated.
[en] ÚJV Řež provides complex services in severe accident management to Czech NPPs owned and operated by ČEZ a.s.:Accident progression; Evaluation of source term; Identification of severe accident management strategies; Supporting analyses for optimization; Validation of existing SAMGs; Supporting analyses for control room habitability; Development of layout of hydrogen mitigation system; Fukushima Dai-ichi event accelerated interest of utility (ČEZ) to enhance SAM: Implementation of H2 removal system designed to SA H2 source (2015); Modifications for primary circuit depressurization; Selection of corium localization strategy: VVER-440/213 Dukovany NPP – IVR implemented; VVER-1000/320 Temelin NPP – not yet decided, R&D program initiated 2015 with parts to both strategies IVR and ExVC.
[en] This publication results from a technical meeting on phenomenology and technologies relevant to in-vessel melt retention (IVMR) and ex-vessel corium cooling (EVCC). The purpose of the publication is to capture the state of knowledge, at the time of that meeting, related to phenomenology and technologies as well as the challenges and pending issues relevant to IVMR and EVCC for water cooled reactors by summarizing the information provided by the meeting participants in a form useful to practitioners in Member States.
[en] Specific features of Loviisa VVER-440: – low power density; – large water volumes =► long time delays =► low decay power; –ice condenser =► flooded cavity. Molten pool heat transfer: – Maximum heat loads assumed to occur when a quasi-steady state has been reached (heat losses from RPV match the decay power); –Stratified pool: • oxidic, heat generating pool at the bottom; • metallic layer on top.
[en] Conclusion: IVR is one of important severe accident management strategies of CAP1400. The purpose of IVR-ERVC experiments is to obtain CHF at RPV lower head and research its relevant mechanism. IVR-ERVC experiment facility was designed and built with a series of improvements. Insights achieved in IVR-ERVC experiments contribute to IVR evaluation, design improvement and safety review of CAP1400.
[en] Goals: – Develop the fundamental scientific basis to understand, predict, and measure changes in materials and systems, structures and components (SSCs) as they age in environments; – Apply this knowledge to develop and demonstrate methods and technologies that support safe and economical long-term operation of existing reactors; – Research new technologies that enhance plant performance, economics, and safety.