Influence of corium temperature, concrete composition and water injection time on concrete ablation during MCCI: New insights (original) (raw)
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The characterization of molten corium–concrete interaction (MCCI) has increasingly become a cause of concern because, in the case of a severe nuclear accident, the core could meltdown and release radiation into the environment. The objective of this study was to determine the thermochemical impact of metal content in the corium and analyze the effect of corium metal content on ablation depth, corium temperature, its viscosity and surface heat flux, and production of hydrogen, carbon monoxide, and carbon dioxide. The governing heat transfer equations were solved while considering the various thermochemical reactions in the existing numerical code in a comprehensive way. The developed MCCI model in CORQUENCH was validated against the data available in the literature. Our findings showed that the composition of corium, especially its metal content, has a noticeable effect on mitigating or aggravating the ablation depth and nuclear reactor integrity. We observed that during molten coriu...
Energies
A postulated progressing severe accident scenario has been simulated using MAAP5 code with the focus on ex-vessel cooling of molten corium in the reactor cavity. Various parameters associated with the prediction of molten corium–concrete interaction (MCCI) are identified. Accordingly, a sensitivity analysis is performed to assess the impact of these parameters on the predicted cavity floor erosion depth during this MCCI postulated accident. The sensitivity index of each variable parameter is determined using the Cotter indices method and Sobol′ indices method. At the early stage of the accident, the predicted cavity floor erosion depth is found to be highly sensitive to the downward heat transfer coefficient parameter with Cotter and Sobol′ indices of 94% and 50%, respectively. At the late phase of the accident, however, the cavity floor erosion depth becomes sensitive to melt eruption (Cotter index of 40%), water ingression (Cotter index of 13%), and particulate bed (Cotter index o...
Nuclear Engineering and Technology
In the present study, the cavity module of the MELCOR code is used for the simulation of molten corium concrete interaction (MCCI) during the late phase of postulated large break loss of coolant (LB-LOCA) accident in the APR1400 reactor design. Using the molten corium composition data from previous MELCOR Simulation of APR1400 under LB-LOCA accident, the ex-vessel phases of the accident sequences with long-term MCCI are recalculated with stand-alone cavity package of the MELCOR code to investigate the impact of water ingression and melt eruption models which were hitherto absent in MELCOR code. Significant changes in the MCCI behaviors in terms of the heat transfer rates, amount of gases released, and maximum cavity ablation depths are observed and reported in this study. Most especially, the incorporation of these models in the new release of MELCOR code has led to the reduction of the maximum ablation depth in radial and axial directions by ~38% and ~32%, espectively. These impacts are substantial enough to change the conclusions earlier reached by researchers who had used the older versions of the MELCOR code for their studies. and it could also impact the estimated cost of the severe accident mitigation system in the APR1400 reactor.
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The MELCOR and CORQUENCH codes are used for simulations of the late phase of a postulated total SBO at KWU KONVOI PWR reactor. The base line SBO sequence without any mitigation and some of its variants are simulated in detail with MELCOR, selected cases up to 10 days of the accident progression. The ex-vessel phases of these scenarios, with long-term molten core-concrete interactions (MCCI), are recalculated also with the specialized code CORQUENCH. The AM counter measures after the reactor pressure vessel failure, typically flooding of the melt by water from the top at different times, are taken into account. The incentive for the work was to investigate the retention of corium materials, which were subject to MCCI, for this particular type of containment. At the same time, the detailed analysis is performed of the effect of different models employed for the description of heat transfer at the melt-concrete interface (ablation modeling) and of the effect of the "coolability" models. The results of the calculations indicate that this type of the KONVOI containment is relatively resistant to challenges by the late-phase accident progression. The incorporation of the CORQUENCH coolability models into MELCOR/CORCON, where it is missing, should be of primary interest. The model of the heat conduction into concrete behind the ablation front could also be useful. The overall impact of this modeling option-which is available in CORQUENCH and not available in MELCOR-on the maximum ablation depth seems to be relatively high under conditions pertaining to our accident simulations.
Large Scale Vulcano Molten Core Concrete Interaction Test Considering Fukushima Daiichi Condition
2019
Fuel debris removal is one of the most important processes for decommissioning a severely damaged nuclear power plant (NPP) such as Fukushima Daiichi NPP (1F). In order to develop relevant removal tools, characteristics of fuel debris are required. Assuming that the test products generated in a MCCI experiment under similar conditions to 1F have similar characteristics to that encountered in actual 1F MCCI products, a VULCANO MCCI test was performed in order to obtain prototypical corium samples and analyze them. The objective of the test was to reach a concrete ablation ratio ΔV/V (where ΔV is the concrete ablation volume, and V is the initial corium volume) close to the concrete ablation ratio of 1F unit 1 (1F1) estimated with the MCCI simulation code TOLBIAC-ICB (~1.6 for 3 days of MCCI). The test named VF-U1 was carried out on January 19, 2017. About 40 kg of a metal and oxide corium pool has been obtained thanks to inductive heating. Corium was directly melt into the test secti...
Molten core concrete interaction test in VULCANO facility preventing initial interfacial crusts
2018
In the frame of the Severe Accident Facilities for European Safety Targets (SAFEST) project, Karlsruhe Institute of Technology (KIT) and the Society for installation and Reactor Safety (GRS) have proposed to realize a Molten Corium Concrete Interaction (MCCI) test in the VULCANO facility located at the PLINIUS experimental platform, CEA Cadarache. The MCCI test, named VBES-U5, was carried out on July 20 th , 2017. 50kg of thermite has reacted to melt a prototypic corium in a siliceous concrete test section, which was then heated by induction. The test section was 2D cylindrical with an inner diameter of 250 mm, an outer diameter of 500 mm, an inner height of 300 mm and outer height of 475 mm. MCCI was carried out for 40 min which conducted to an axial ablation of 10 mm and a radial ablation of 60 mm. Great care has been taken to prevent initial crust formation (corium composition such that initial contact temperature is above solidus, high power during the first minutes). Nevertheless, a pronounced radial ablation has been observed for this siliceous concrete, similarly to previous VULCANO tests in which initial crust formation was likely to occur.
Benchmarking work was recently performed for the issue of molten corium concrete interaction (MCCI). A synthesis is given here. It concerns first the 2D CCI-2 test with a homogeneous pool and a limestone concrete, which was used for a blind benchmark. Secondly, the COMET-L2 and COMET-L3 2D experiments in a stratified configuration were used as a post-test (L2) and a blind-test (L3) benchmark. More details are given here for the recent benchmark considering a matrix of four reactor cases, with both a homogeneous and a stratified configuration, and with both a limestone and a siliceous concrete. A short overview is given on the different models used in the codes, and the consistency between the benchmark actions on experiments and reactor situations is discussed. Finally, the major uncertainties concerning MCCI are also pointed out.
Two-dimensional interaction of oxidic corium with concretes: The VULCANO VB test series
Annals of Nuclear Energy, 2009
Three two-dimensional Molten Core-Concrete Interaction tests have been conducted in the VULCANO facility with prototypic oxidic corium. The major finding is that for the two tests with silica-rich concrete, the ablation was anisotropic while it was isotropic for limestone-rich concrete. The cause of this behaviour is not yet well understood.
Fire Technology
This paper presents some experimental and numerical results on the study of the hygrothermal behavior of the High Performance Concrete used to build the inner wall of the nuclear power station of CIVAUX 2 (in France). In the laboratory, accidental situations (beyond design) have been considered. The scenario, designated as Severe Accident (SA), consisted of a rise from ambient conditions to 200C, and a steam pressure of 1.3 MPa in 24 hours, maintained after several hours. Those conditions were applied on one face of a specimen, the other one being in ambient temperature. A cylindrical specimen with 1.3 m of thickness was used. Thermocouples, pressure taps, and moisture meters were implanted in the concrete at the moment of casting. They gave local information; most of them are distributed in the first 0.30 m. The typical experimental results of the evolution of the temperature, the pressure and water content as a function of time, are shown for the testing conditions. The thickness ...