Search Results (16)

Puffballs, a group of macrofungi belonging to the Basidiomycota, pose taxonomic challenges due to their convergent morphological features, including spherical basidiocarps and similar peridial structures, which often hinder accurate species-level identification. This study proposes a deep learning-based classification framework for eight ecologically and taxonomically important puffball species: Apioperdon pyriforme, Bovista plumbea, Bovistella utriformis, Lycoperdon echinatum, L. excipuliforme, L. molle, L. perlatum, and Mycenastrum corium. A balanced dataset of 1600 images (200 per species) was used, divided into 70% training, 15% validation, and 15% testing. To enhance generalizability, images were augmented to simulate natural variability in orientation, lighting, and background. In this study, five different deep learning models (ConvNeXt-Base, Swin Transformer, ViT, MaxViT, EfficientNet-B3) were comparatively evaluated on a balanced dataset of eight puffball species. Among these, the ConvNeXt-Base model achieved the highest performance, with 95.41% accuracy, and proved especially effective in distinguishing morphologically similar species such as Mycenastrum corium and Lycoperdon excipuliforme. The findings demonstrate that deep learning models can serve as powerful tools for the accurate classification of visually similar fungal species. This technological approach shows promise for developing automated mushroom identification systems that support citizen science, amateur naturalists, and conservation professionals. Full article

The thermophysical properties of corium are critical for improving the predictive accuracy of severe accident analysis codes. However, due to the high melting temperature and high volatility of corium, thermophysical property measurements are extremely challenging, resulting in a significant lack of data. This study presents a non-contact measurement facility based on the aerodynamic levitation technique, enabling the measurement of the density, surface tension, and viscosity of corium components at temperatures exceeding 3000 K. Density is measured based on the axisymmetric ellipsoid assumption of levitated drops, while the surface tension and viscosity are determined using the drop oscillation method. Experimental results for key corium components, including ZrO₂ and a UO₂-ZrO₂ mixture, are presented, addressing data gaps in the thermophysical properties of UO₂-containing materials. Full article

In a severe accident, molten corium may penetrate the reactor pressure vessel and enter the cooling water in the reactor cavity, and then a steam explosion may occur. Steam explosions can initiate pressure waves and threaten the structural integrity of the reactor cavity. To investigate the propagation characteristics of the pressure waves, including the propagation pattern, attenuation, and amplification under TNT detonation, a coupled numerical approach combined with arbitrary Lagrangian–Eulerian and fluid–structure interaction methods are utilized. The peak pressures of the incident and reflected shock waves decrease rapidly with increasing distance from the charge center, whereas the reflected pressure in the reactor cavity can be between 1.30 and 1.67 times the incident pressure. Then, structural analysis is performed to evaluate the damages to the concrete, liner plate, and reinforcements. From the numerical results, localized and superficial concrete damages are observed in the reactor cavity and the basemat; however, the risk of damage to the concrete, resulting in the collapse of these components is very low. The risk of damage to the liner plate and reinforcements is also very low since the maximum strain values are much lower than the failure criteria. Finally, the structural integrity of the reactor cavity will be maintained during the TNT detonation for the steam explosion. Full article

Medicinal signaling cells (MSC) exhibit distinct molecular signatures and biological abilities, depending on the type of tissue they originate from. Recently, we isolated and described a new population of stem cells residing in the coronary corium, equine hoof progenitor cells (HPCs), which could be a new promising cell pool for the treatment of laminitis. Therefore, this study aimed to compare native populations of HPCs to well-established adipose-derived stem cells (ASCs) in standard culture conditions and in a pro-inflammatory milieu to mimic a laminitis condition. ASCs and HPCs were either cultured in standard conditions or subjected to priming with a cytokines cocktail mixture. The cells were harvested and analyzed for expression of key markers for phenotype, mitochondrial metabolism, oxidative stress, apoptosis, and immunomodulation using RT-qPCR. The morphology and migration were assessed based on fluorescent staining. Microcapillary cytometry analyses were performed to assess the distribution in the cell cycle, mitochondrial membrane potential, and oxidative stress. Native HPCs exhibited a similar morphology to ASCs, but a different phenotype. The HPCs possessed lower migration capacity and distinct distribution across cell cycle phases. Native HPCs were characterized by different mitochondrial dynamics and oxidative stress levels. Under standard culture conditions, HPCs displayed different expression patterns of apoptotic and immunomodulatory markers than ASCs, as well as distinct miRNA expression. Interestingly, after priming with the cytokines cocktail mixture, HPCs exhibited different mitochondrial dynamics than ASCs; however, the apoptosis and immunomodulatory marker expression was similar in both populations. Native ASCs and HPCs exhibited different baseline expressions of markers involved in mitochondrial dynamics, the oxidative stress response, apoptosis and inflammation. When exposed to a pro-inflammatory microenvironment, ASCs and HPCs differed in the expression of mitochondrial condition markers and chosen miRNAs. Full article

Two crystalline phases, which are analogues of common secondary uranyl minerals, namely, becquerelite (Ca[(UO₂)₆O₄ (OH)₆]·8H₂O) and phurcalite (Ca₂[(UO₂)₃O₂ (PO₄)₂]·7H₂O) were identified on the surface of a Chernobyl corium-containing sample affected by hydrothermal alteration in distilled water at 150 °C for one year. Phases were characterized using Single-Crystal X-ray Diffraction Analysis (SCXRD) as well as optical and scanning electron microscopy. Features of the structural architecture of novel phases, which come from the specific chemical composition of the initial fragment of Chernobyl sample, are reported and discussed. Precise identification of these phases is important for modelling of severe nuclear accidents and their long-term consequences, including expected corium–water interaction processes at three damaged Units of the Nuclear Power Plant Fukushima Daiichi. Full article

The core catcher is arranged in an unattended, unventilated sub-reactor space. It is designed to receive molten corium in emergencies, and thus the concrete used in the core catcher must be resistant to high temperatures without significant loss of strength. During nuclear power plant (NPP) operation, these concretes are subjected to considerable radiation exposure, which may also affect their physical–chemical properties. Concrete mixes based on Portland cement and alumina cement with iron and corundum aggregate were investigated. Model samples of concrete were subjected to temperature exposure in the temperature range of 100 to 1000 °C and to radiation exposure in the field of mixed and neutron irradiation in the reactor cell at a load of at least 1 × 10⁷ Gy. Concrete heating over 200 °C leads to a decrease in strength characteristics from 25.1 MPa to 2.6 MPa in Portland cement-based concretes and from 40 MPa to 12 MPa in alumina cement-based concretes. The decrease in concrete strength at high temperatures is due to dehydration of hardening phases, polymorphic transitions of aggregate and chemical interaction between concrete components. Radiation exposure of Portland cement-based concrete samples leads to an increase in their strength. Alumina cement-based concretes are less resistant to radiation exposure, and their strength decreases as a result of radiation exposure-induced processes. Full article

Thirty-four species of Triatominae (Hemiptera, Reduviidae) are recorded in Mexico, Triatoma Laporte, 1832 the most speciose genus in this country. Here, we describe Triatoma yelapensis sp. nov. from the Pacific coast of Jalisco (Mexico). The most similar species to T. yelapensis sp. nov. is T. recurva (Stål, 1868), but they differ in head longitude, the proportion of labial segments, coloration pattern of corium and connexivum, spiracles location, and male genitalia. To provide statistical support for the morphological distinctiveness of the new species, we performed a geometric morphometric analysis of T. yelapensis sp. nov., T. dimidiata s.s. (Latreille, 1811), T. gerstaeckeri (Stål, 1859), and T. recurva (Stål, 1868), considering head morphology. We also provide an updated key of the genus Triatoma for species recorded in Mexico. Full article

This paper presents the results of computational and physical studies on the production of corium and its retention in an MR’s melt trap of the Lava-B facility. A feature of the Lava-B facility used in the IAE NNC RK to study the processes occurring during a severe accident at a nuclear reactor, is the separation of the stages of the reactor core corium formation and its interaction with structural materials. The melting of materials takes place in an induction furnace with a hot crucible, after which it moves to a melt receiver (MR) in which the test object is located. In the case of studies of processes occurring outside the reactor vessel, this is a special trap, which is placed in the inductor to simulate decay heat. However, based on the conservative computational estimates, it was found that the inductor power in the MR can be sufficient to directly produce, melt, and, subsequently, maintain the corium in the liquid phase. In this regard, in order to optimize the experiments under controlled conditions, the authors came up with the idea to experimentally test the possibility of producing corium by induction heating directly in the MR’s melt trap. In addition, according to the authors, this method would obviate the problem of corium contact with the carbon environment of the melting furnace of the Lava-B facility. Previously, burden heating simulating corium was modeled on the computer using available parameters of the MR’s induction heater. Based on the numerical experiment, the conditions for physical modeling of the corium production in the MR’s melt trap were established. An analysis of the physical modeling showed that during the burden heating in the melt trap, its metal components became liquid, thus, forming a melt pool. However, in terms of this design of the trap, there were problems associated with the complete melting of all corium components, as well as with the integrity of the experimental device when forming the corium pool and during the actual physical modeling. Full article

This research presents a computational investigation of the thermal convection of a heat-generating liquid having variable viscosity in a semi-cylindrical cavity. The analysis is carried out to obtain the time patterns of the average Nusselt number at the lower border of the chamber and understand the impact of the variable viscosity, the Prandtl number, and the Rayleigh number on this parameter. The natural convection in the cavity is defined by the set of non-dimensional equations based on the Boussinesq approach employing the non-primitive parameters such as vorticity and stream function. These governing equations are worked out numerically based on the finite difference technique. The time dependencies have been obtained at the Rayleigh number equal to 10⁴, 10⁵, and 10⁶ and the Prandtl number taking values of 7.0, 70, and 700. The results obtained for variable and constant viscosity have been compared. Additionally, the paper represents maps of isotherms and streamlines for the mentioned values of the Rayleigh number. The influence of variable viscosity on the parameters of natural convection is poorly studied in closed systems; therefore, this research gives necessary data to understand the general time nature of the average Nusselt number at cooling surface of various parameters. Additionally in this research, the model for simulating the natural convection in non-primitive variables is presented in polar coordinates when the dynamic viscosity varies with temperature. The computational model designed could be used to simulate the free convection in systems with inner heat production such as chemical reactors, inductive metal melting facilities, or corium in-vessel retention to analyze the impact of various factors on the parameters of the natural convection in such systems. Full article

This paper is devoted to the creation of an information and analytical system (IAS) which is under development to manage the data obtained in experiments and investigations to justify the safety of atomic energy, which the National Nuclear Center of the Republic of Kazakhstan (RSE NNC RK) has been conducting for over 30 years. The main components of the IAS determining its consumer capabilities is an analytical unit that will allow the creation of programs for planned experiments in view of the technical requirements for them and based on the results of previous experiments, generalized and consolidated by processing and comparison tools provided by the IAS. An important component of the IAS is a set of tools for the predictive calculation of the temperature of materials of test sections depending on a given change in the power of energy release in them, predictive calculation of the required power of energy release in materials depending on a given change in their temperature, formation of arrays of experimental information in digital format and graphical form, comparison of experiments and their data among themselves, and the formation of protocols of experiments with the possibility of choosing specific data and methods for their processing. It should be noted that the created IAS greatly simplifies the preparation for experiments. Full article

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 of 15%) parameters alongside the downward heat transfer coefficient (Cotter index of 16%) with the melt eruption parameter becoming dominant. Thus, the sensitivity of the code′s predictions can be minimized by improving the physical models associated with these parameters. Moreover, the sensitivity indices of these parameters can be used by model developers to identify unimportant parameters in a bid to reduce the dimension of the problem with the aim of improving the current predictive capabilities to conduct MCCI-related safety analyses. Full article

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 corium–concrete interaction, zirconium plays a significant role and its presence can increase the ablation depth exponentially from 18.5 to 139 cm in the investigated case study. It was found that the presence of zirconium in the corium instigated various thermochemical reactions continuously, and thus the injected water, instead of quenching the molten corium, enhances the temperature by facilitating exothermic reactions. Additionally, due to the presence of zirconium, the production of hydrogen and carbon monoxide increases by 45 and 52 times, respectively and the generation of carbon dioxide becomes zero because the zirconium reacts with carbon dioxide continuously, converting it to carbon monoxide. Full article

Osseointegration of implants installed in conjunction with sinus floor elevation might be affected by the presence of residual graft. The implant surface characteristics and the protection of the access window using a collagen membrane might influence the osseointegration. To evaluate these factors, sinus floor elevation was performed in patients using a natural bovine bone grafting material. The access windows were either covered with a collagen membrane made of porcine corium (Mb group) or left uncovered (No-Mb group) and, after six months, two mini-implants with either a moderate rough or turned surfaces were installed. After 3 months, biopsies containing the mini-implants were retrieved, processed histologically, and analyzed. Twenty patients, ten in each group, were included in the study. The two mini-implants were retrieved from fourteen patients, six belonging to the Mb group, and eight to the No-Mb group. No statistically significant differences were found in osseointegration between groups. However, statistically significant differences were found between the two surfaces. It was concluded that implants with a moderately rough surface installed in a composite bone presented much higher osseointegration compared to those with a turned surface. The present study failed to show an effect of the use of a collagen membrane on the access window. Full article

Considering transient processes where liquid/solid phase change occurs, this paper focuses on the associated modeling and numerical treatment in the frame of “Computational Fluid Dynamics” simulations. While being of importance in many industrial applications involving solidification and melting of mixed materials, including power and manufacturing engineering, the first application of this work pertains to the analysis of severe accidents in a nuclear reactor. Indeed, in this context, the molten core materials (a.k.a. corium) can form a high-temperature multiphase liquid pool at the boundary of which fusion and solidification phenomena are of prime importance. In this context, even if materials at play are treated as pure components, it is mandatory to distinguish two different phase change temperatures with a solid fusion temperature and a liquid solidification temperature. Accordingly, in the frame of a sharp interface representation, the paper introduces non-classical heterogeneous conditions at the liquid/solid boundary in such a way that both moving interface (through Stefan conditions associated with fusion or solidification) and static interface (imposing heat flux continuity) are supported at the same time on different spatial locations along this boundary. Within a monolithic resolution of Navier–Stokes and heat conduction equations, this interface is explicitly tracked with combined Front-Tracking and VOF methods. In order to ensure zero velocity in the solid phase, an Immersed Boundary Method and a direct forcing penalization are also introduced. The main relevant features of this combination of numerical methods are discussed along with their implementation in the TrioCFD code taking advantage of the pre-existing code capabilities. Numerical simulations including both verification tests and a case of interest for our industrial application are reported and demonstrate the applicability of the proposed triptych model+methods+code to treat such problems. The numerical tools and the simulation code developed in this work could be used not only in the several accident context but also to simulate melting, solidification and fusion processes occurring in aerodynamics, hypersonic reentry vehicles and laser applications to cite but a few. Full article

More than 30 years ago a specialist meeting was held at Joint Research Center Ispra (Italy) from 15 to 17 January 1990 to review the current understanding of chemistry during severe accidents in light water reactors (LWR). Let us consider that, at the end of the 1980s, thermodynamics introduced in the severe accident codes was really poor. Only some equilibrium constants for a few simple reactions between stoichiometric compounds were used as well as some simple correlations giving estimates of solidus and liquidus temperatures. In the same time, the CALPHAD method was developed and was full of promise to approximate the thermodynamic properties of a complex thermochemical system by the way of a critical assessment of experimental data, a definition of a simple physical model and an optimisation procedure to define the values of the model parameters. It was evident that a nuclear thermodynamic database had to be developed with that new technique to obtain quite rapidly prominent progress in the knowledge of thermochemistry in the severe accident research area. Discussions focused on the important chemical phenomena that could occur across the wide range of conditions of a damaged nuclear plant. The most pressing need for improved chemical models is identified with condensed phase mixtures to model the corium progression. This paper reviews more than 30 years of experimental data production in the field of corium thermodynamics. This work has been conducted through multiple international programs (EURATOM, ISTC, OECD) as well as through more specific studies conducted at the national scale. This research has been capitalised in specific databases such as NUCLEA and TAF-ID, databases developed at IRSN and at CEA, respectively, and are now used in degradation models of the severe accident simulation codes. This research is presented in this paper. In the conclusion, we outline the research perspectives that need to be considered in order to address today’s and tomorrow’s issues. Full article