[en] Mass transfer in sodium fast reactors (SFRs) has been extensively studied in the past years, but no consideration on the effect of irradiation on this phenomenon was included in the corrosion equations. Moreover, some discrepancies exist on the mass loss rates obtained at low temperatures and low oxygen content. In this paper, new equations for mass loss are proposed from literature examination, separating the loss by preferential leaching (alloy element dissolution) from general corrosion, and integrating the effect of the diffusion enhancement by irradiation. The effect of irradiation is considered by estimating the diffusion coefficient enhancement due to point defect creation. It is found that the mass losses could be one order of magnitude higher than the values given by several mass transfer models. Depending on the choice of kinetic parameters, the irradiation can account at the most for 70% of the increase. This approach shows that mass transfer codes should take into account elements that were formerly neglected: low temperature corrosion (with correct contributions of preferential leaching and general corrosion), irradiation and saturation.
Journal
[en] The oxidation of graphite in normal operating conditions is a very important factor when evaluating the service time of the graphite structural material in a high temperature gas-cooled reactor (HTGR). This paper deals with the modeling of graphite oxidation by steam in the helium channel of a fuel block. The FEM software COMSOL is used: the turbulent flow of the coolant is simulated by using the k-ε model and the chemical reaction is expressed by the Langmuir-Hinshelwood equation. Calculations were carried out for steam pressures around 1 Pa and for different temperature distributions. The influence of burn-off and the diffusion in graphite porosities were both considered in the oxidation. Results show that oxidation mainly occurred on the graphite surface at the bottom of the core because of the higher temperature. The thickness of graphite with a burn-off higher than 8% was about 1 mm at the core base. Less than 15% of steam was consumed in the coolant channel of the fuel assemblies. Calculations also showed that the mean gasification rate in one channel for the second service time was larger than the first service time
Journal
[en] The characteristics of fuel debris are required to develop tools to remove it from severely damaged nuclear power plants, but the knowledge on molten core concrete interaction (MCCI) product is limited. The VULCANO MCCI test campaign, VBS-U4, was selected for the analysis as the conditions are similar to MCCI at Fukushima daiichi nuclear power plant. Physicochemical phenomena during MCCI were estimated from the macrostructure of the samples. Moreover, heterogeneous microstructure of the oxide region and homogeneous microstructure of the metallic region was confirmed. Additionally, the obvious difference of Vickers hardness between oxide and metallic phase is evaluated. (author)
Journal
Progress in Nuclear Science and Technology; ISSN 2185-4823; 
; v. 5; p. 217-220
; v. 5; p. 217-220
[en] Optimizing melt spreading in the aftermath of a core disruptive accident is crucial for achieving sufficient melt cooling to maintain reactor containment integrity. Two approx. = 30 kg-scale experiments performed at the VULCANO facility explore the spreading of high-temperature molten corium-concrete mixtures over ceramic and sacrificial concrete substrates. Imaging of the melt front propagation revealed a 7% increase in spreading length and a 30% increase in maximum front velocity during spreading over sacrificial concrete, despite a reduced mass partaking in spreading due to increased holdup within the crucible. Infrared imaging of the melt indicated surface temperatures around 45℃ lower during spreading on sacrificial concrete, resulting in a roughly three-fold increase in melt viscosity. The enhanced viscosity and reduced mass during the VE-U9-concrete test imply an increased spreadability on sacrificial concrete greater than the observed 7% increase in spreading length. This enhanced spreadability on sacrificial concrete could be explained by the apparent gliding motion of the melt, consistent with reduced friction at the melt-substrate interface. Reduced friction at the melt-substrate interface is best explained by a diphasic film of molten concrete and gaseous concrete decomposition products acting as a lubricant between the melt and solid substrate. (author)
Journal
Journal of Nuclear Science and Technology (Tokyo) (Online); ISSN 1881-1248; ; v. 59(4); p. 446-458
; v. 59(4); p. 446-458
[en] 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. Post Test Examinations have indicated that for the silica-rich concrete, the corium melt mixed specifically with mortar, while, for limestone-rich concretes, the analysed samples were in accordance with a corium-concrete mixing. The experimental results are described and compared to numerical codes. Separate Effect Tests with Artificial Concretes and prototypic corium are proposed to understand the phenomena governing the ablation geometry.
Journal
[en] Characterization of fuel debris is required to develop fuel debris removal tools for decommissioning Fukushima Daiichi nuclear power plant (1F). Especially, knowledge about the characteristics of molten core-concrete interaction (MCCI) product is needed because of the limited information available at present. Samples from a large-scale MCCI test performed under quenching conditions, VULCANO VW-U1 were analyzed to evaluate the characteristics of the surface of MCCI product. Four samples were selected from test sections at different locations. As a result, the characteristics of the samples were found to be similar. Several corium phases, such as cubic-(U,Zr)O2 and tetragonal ZrO2, were detected by X-ray diffraction (XRD), but concrete-based phases, such as the crystalline SiO2 phase, were not detected by XRD because the quantity of the SiO2 phase was too small to be measured. The Vickers hardness of each phase in these samples was higher than that of previously analyzed samples in another VULCANO test campaign, VBS-U4. Based on a comparison between MCCI product generated under quenching condition, such as VW-U1, and gently cooled MCCI product, such as VBS-U4, the MCCI product generated under quenching condition is more homogeneous, and its hardness is higher than that of the gently cooled MCCI product. (author)
Journal
Journal of Nuclear Science and Technology (Tokyo) (Online); ISSN 1881-1248; ; v. 56(9-10); p. 902-914
; v. 56(9-10); p. 902-914
[en] Historically, nuclear science has developed alongside advances in instrumentation for radioactivity measurement and particle detection. Nuclear installations require a whole panoply of instruments for a precise measurement of quantities which characterize their operation, their control, their safety. This specific instrumentation mainly concerns (but not only) the detection of radioactivity, and it must work in a hostile environment with high requirements of accuracy, robustness and reliability. This monograph provides an overview of the measurement and control instruments used in the various fields of civil nuclear energy, from power reactors to radiation protection, including instrumentation for fuel cycle installations, the management of radioactive wastes or the clean-up and dismantling of nuclear installations. The paper shows the diversity and technical nature of the instruments involved, the importance of data assimilation methods resulting from the measurement, and by the extent of the effort devoted to their development by the nuclear community and the CEA
[fr]
Historiquement, les sciences nucleaires se sont developpees parallelement aux progres de l'instrumentation pour la mesure de la radioactivite et la detection de particules. Aujourd'hui encore, l'instrumentation est une science a part entiere, qui fait l'objet d'une recherche active trouvant des applications, en particulier dans l'equipement des installations nucleaires. Celles-ci demandent toute une panoplie d'instruments pour une mesure precise des grandeurs qui caracterisent leur fonctionnement. Il y va de leur controle, et de leur surete. Il s'agit d'une instrumentation specifique puisqu'elle concerne principalement (mais pas seulement) la detection de la radioactivite, et qu'elle doit travailler en milieu hostile avec de grandes exigences d'exactitude, de robustesse et de fiabilite. La presente monographie offre un panorama des instruments de mesure et de controle utilises dans les differents domaines de l'energie nucleaire civile, depuis les reacteurs de puissance jusqu'a la radioprotection, en passant par l'instrumentation pour les installations du cycle du combustible, la gestion des dechets radioactifs ou l'assainissement-demantelement des installations nucleaires. Le lecteur sera sans doute frappe par la diversite et la technicite des instrumentsmis en jeu, l'importance des methodes d'assimilation de donnees issues de la mesure, et par l'ampleur de l'effort consacre a leur developpement par la communaute nucleaire, en general, et par le CEA, en particulierSource
17 Jun 2019; 288 p; Le Moniteur Editions; Paris (France); ISBN 978-2-281-14303-4; ; ISSN 1950-2672; ; 1 refs.
; ISSN 1950-2672; ; 1 refs.
[en] Historically, nuclear science has developed in parallel to the advances of instrumentation for radioactivity measurement and particle detection. Still nowadays, instrumentation is a true science in which research is actively pursued, with applications in particular in the equipment of nuclear facilities. The latter require a broad range of instruments for the quantities characterizing their operation to be accurately measured, a key issue, indeed, for both their monitoring and their safety. This instrumentation is specific as it is mostly (though not only) related to radioactivity detection, and has to be operated in harsh environment with high requirements in accuracy, robustness, and reliability. This Monograph gives an overview of the measuring and monitoring instruments used in the various fields of civilian nuclear energy, ranging from power reactors to radiation protection, going through instrumentation for fuel cycle facilities, radioactive waste management, or clean-up and dismantling of nuclear facilities. The reader will be probably impressed by the diversity and technicality of the instruments involved, the crucial role of methods for using data from measurement, and the considerable effort devoted to their development by the nuclear community as a whole, and in particular by the CEA
Source