The paper presents the results of modeling an L4 experiment using an ACE test facility (USA) on the interaction of the melt with concrete. The study aims to validate previously developed models of interaction between the melt and concretes of two particular types used in the construction of VVER-1000 NPPs. The experimental and calculation results were compared according to the movement of the concrete erosion boundary, the integral yield of hydrogen, carbon monoxide, and vapors of structural materials, as well as simulators of melt fission products. A satisfactory agreement was obtained according to all characteristics. The scatter of the results at the variation of main calculation parameters was estimated along with the degree of their influence on the concrete penetration depth.

The authors have described the key features of approaches to numerical modeling of the interaction of the core melt of a water-moderated water-cooled power reactor with the NPP structures, that are aimed at accelerating the cal- culation to preserve the approximation by using 0D + 2D finite-element schemes with an adaptive 2D grid for the wall and a 0D grid for the melt. The composition of the melt of interacting components and their properties, and also the properties of the heating material of the wall are determined in the process of calculation. The given examples of calculations of the thermal erosion of the wall by the melt with in-vessel retention of the melt and melt–concrete interaction illustrate the computational efficiency of the proposed approaches.

Vivianite, an authigenic mineral from the phosphate class, was discovered in Kara Sea bottom sediments for the first time. Similar finds of vivianite were previously known only for the outer shelf of the Laptev Sea, the northern Barents Sea, and the eastern White Sea. Its presence in the subsurface sedimentary strata indicates desalinization of the surface layer of the sea. Core 7444, sampled in a tectonic depression in the Kara Sea during the first stage of cruise 89 of the R/V Akademik Mstislav Keldysh (2022), uncovered Holocene sedimentary strata up to 6.19 m thick. Coarse-silty and sandy vivianite formations are found throughout the entire core, starting from 0.11 m. Vivianite was investigated by a set of methods: optical microscopy, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy. The morphology, microstructures, and chemical composition of vivianite formations have been studied. Three morphological types of these formations have been identified: micronodules and their intergrowths, crystalline aggregates and their intergrowths, and tubular aggregates.

The results of a simulation of ACE MCCI test L8 facility (ANL, Argonne, USA) on the interaction of melt with concrete are presented. The objectives of this work are the validation of previously developed models of the melt–concrete interaction and an analysis of inconsistencies in the yield of carbon oxides, which are explained by aspects of the thermochemistry of the interaction. The computational and experimental results were compared by way of the advancement of erosion boundary of the concrete, the yield of hydrogen and carbon oxides from the melt, and the integral yield of the fission-product imitators. The agreement is satisfactory. The spread of the results on varying the main parameters of the calculation was assessed.

The studies have shown that the distribution of suspended particulate organic carbon in the seas of the Russian Arctic is characterized by сircumcontinental and vertical zonalities. These zonalities are manifested in decreasing concentrations and therefore fluxes (mgC/m2 /day) of suspended particulate organic carbon in the transition from the near-continental to pelagic areas of the Arctic Ocean, as well as from the surface photic layer to the near-bottom layer by two orders of magnitude, which is confirmed by instrumental data of sedimentation traps and correlates with the zoning of bio-production processes.

The paper considers refined approaches to solving two problems of modeling MCCI: (1) a thermodynamical model of chemical reactions of the concrete components with the melt was constructed, as well as a model of concrete decomposition including universal procedures for calculating the heat capacity and density of concrete, independently on its type; (2) a self-consistent, cost-effective model of concrete ablation progression was constructed, taking into account heating of the concrete; this model numerically solves the heat conduction equation on an adaptive grid. The models are described and verified.

Heat transfer in a drained channel of RBMK-1000 as it heats up during a severe beyond design basis LOC accident with destruction of the core is considered. Radiative heat exchange of a FA with a channel tube, in conjunction with molecular heat exchange in FA and the graphite column enclosing the channel is calculated. This is accomplished by means of precision models of heat transfer, based on ray tracing with adjustable spatial resolution. The calculated temperature behavior is determined by the well-known effect of the heat capacity of a graphite column, in the present case under the conditions of a beyond design basis accident, due to which the core and FA slowly heat up. This has the result that the fuel-rod cladding can heat up while the channel almost completely drained and in the absence of a developed steam-zirconium reaction. The obtained results could be helpful in building simplified approaches to modeling heat transfer in a RBMK-1000 core during a severe accident.

A spatio-temporal dependence between the vertical fluxes of the deposited matter (according to the data of sediment traps (mg/m2/day)) and the mass concentration of suspended matter (mg/L) has been revealed. Using satellite data of the optical range (using the spectral channels of the MODIS–Aqua 531 and 551 nm scanner, the backscattering index by suspended particles (bbp, m–1) was calculated), it became possible to continuously obtain (for the ice-free period) monthly average data on the values of the vertical flux of sedimentary matter from the surface layer for the entire sea.

Выявлена пространственно-временная зависимость между вертикальным потоком осаждающегося вещества (по данным седиментационных ловушек (мг/м2/сут)) и массовой концентрацией взвеси (мг/л). Используя спутниковые данные оптического диапазона (с помощью спектральных каналов сканера MODIS–Aqua 531 и 551 нм рассчитывался показатель рассеяния назад взвешенными частицами (bbp, м–1)), стало возможным непрерывно получать (для безледного периода) среднемесячные данные о величинах вертикального потока осадочного вещества из поверхностного слоя для всего моря.

A neutron collimator is developed to attenuate the neutron flux and reduce the residual induced activity in the interportal space of the diagnostic system of neutral particle analyzers of the ITER tokamak reactor. The collimator is installed in the port plug of the ITER vacuum vessel in front of an inlet to the vacuum pipeline of the diagnostic system. The collimator design has a cellular structure with 80% transparency for the neutral atom beam that goes out of the plasma and is recorded by the analyzers. However, because of increased scattering of neutrons in the collimator, their flux in the interportal room in the service zone of diagnostic systems of equatorial port no. 11 is significantly reduced and allows the equivalent dose rate in this zone to be decreased by several times. Thermal analysis showed that, during the reactor operation in modes with generation of the maximum power of 500 MW, the plasma radiation will cause the heating of the collimating grid to a temperature not exceeding 250°C, which makes it possible to select the stainless steel (316L(N)-ITER grade) as a material for manufacturing the collimator. In this case the cyclic strength of the collimator meets the ITER requirements, and it can be used without replacement during the entire deuterium-tritium experiment of the tokamak reactor.

НЕЙТРОННЫЙ КОЛЛИМАТОР ДЛЯ ДИАГНОСТИЧЕСКОЙ СИСТЕМЫ АТОМНЫХ АНАЛИЗАТОРОВ ТОКАМАКА-РЕАКТОРА ИТЭРА.С.Наволоцкий 1 , В

A model of radiative heat-exchange, based on the Rosseland approximation, in a gas cavity was introduced into the HEFEST computational code designed for modeling the interaction of the core melt with NPP structures during a serious accident in VVER. This approach is admissible for optically dense gas and supplements the zonal heat exchange model, already existing in the code, for a cavity with a transparent gas. The conditions for using these two approaches in modeling radiative heat transfer at different stages of an accident are discussed. The numerical implementation of the diffusion model and its verification are described. The model was tested on the problem of radiative heat exchange during melt retention at the bottom of the vessel of a VVER-1000 reactor and the results are reported.

Heat transfer in the gas cavity of the melt trap for the VVER-1200 core is studied. A model problem is solved numerically in a configuration where the cavity boundaries are close to that obtained after the formation of the melt pool. Heat transfer by radiation is calculated by three methods: in the approximation of a transparent medium taking account of the angular coefficients of radiation emission of sections of the cavity boundaries, by the DTRM method suitable for calculating radiation transfer in a medium with arbitrary optical density, and by the diffusion method in the Rosseland approximation. It is shown that the dominant mechanism is thermal radiation; the contribution of convection of the gas is relatively small. The influence of the choice of computational method on heat transfer in a gas cavity with different absorption is evaluated.

A model of a passive autocatalytic hydrogen recombiner (RVK-500, -1000) for use in hydrodynamic calculations of hydrogen transport and recombination processes in a VVER containment shell during a severe accident is described. The model includes calculation of the efficiency of the recombiner, the hydraulic resistance to gas flow through the recombiner, and heat losses owing to radiation from the casing of the recombiner. The model was parameterized and verified on experiments performed on a stand at VTI and INPK RET for hydrogen-air compositions with hydrogen volume fraction up to 10%. Good agreement was obtained between the calculations and experiments. Its simplicity and efficacy make it possible to use the model in hydrodynamic calculations of processes with recombiners in a real containment shell.

Computational hydrodynamics was used to perform, within the scope of the ERCOSAM–SAMARA international projects, calculations of the S1, S2 experiments on the SPOT ZO setup with a condenser-heat exchanger. The basic effects observed in the experiments are reproduced: helium pressure growth and stratification upon injection, pressure reduction and partial elimination of stratification during the operation of the condenser-heat exchanger. On the whole, the experiment agreed well with the calculations of the pressure, temperature, and composition of the gas. The small quantitative discrepancies with experiment indicate a possible impact of neglected factors, mainly, associated with inadequate knowledge of the details of the condensation/evaporation processes at and near the walls as well as with general sensitivity to variations of the initial conditions. Specifically, the deviation of the initial wall temperature or the total heat capacity of the wall appreciably influences the behavior of the pressure.

One of the experiments of ERCOSAM-SAMARA (E-S) projects (TOSQAN T114) is examined from the viewpoint of the radiative heat transfer (RHT) contribution to the overall heat exchange. E-S projects and T114 test were focused on investigation of light gas stratification in severe accident containment atmosphere and stratification break-up after the activation of mitigation systems. The first from two phases of T114 test is considered during which helium is quasistatically injected into the upper part of the TOSQAN vessel having isothermal walls and initially filled by air. The developing free convection removes most of the heat acquired, but not all. Thus stable local deviations in calculated temperatures were obtained in simulations that were interpreted as the deficiencies of the physical heat-transfer model. The modeling of RHT was included in full CFD simulation that resulted in a better agreement in local temperatures. The results of comparative calculations performed without/with RHT modeling are described in the paper. The RHT model implemented in the used CFD code (ANSYS FLUENT) was tested on known analytical solutions. The RHT contribution in T114 test was also estimated analytically to demonstrate independently that it may be noticeable in this experiment. The same estimations may be valid for stagnant zones of severe accident containment. All that shows the need in further detailing of the role of RHT in gas structure heat exchange: as for interpretation of some containment tests performed in pressure vessel as for containment modeling. (C) 2016 Elsevier B.V. All rights reserved.