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Description/Abstract The significance of iodine for source term quantification has been studied by investigating its chemical behavior under the prototypical conditions of a hypothetical severe accident within the containment. As a... more
Description/Abstract The significance of iodine for source term quantification has been studied by investigating its chemical behavior under the prototypical conditions of a hypothetical severe accident within the containment. As a result, some computer codes ...
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ABSTRACT Analyses of severe accidents in nuclear power plants by using integral codes are necessary in order to develop accident management strategies that prevent such accidents or mitigate their consequences for the environment. The... more
ABSTRACT Analyses of severe accidents in nuclear power plants by using integral codes are necessary in order to develop accident management strategies that prevent such accidents or mitigate their consequences for the environment. The most important requirement for the development of integral codes is to achieve good predictability of a given accident scenario through the understanding and quantification of severe accident phenomena and their underlying physical and chemical processes. In this paper, the progress in modeling the processes related to the radioactive source term, and in particular progress related to the release and transport of fission products in the circuit and containment, is demonstrated by the assessment of integral and detailed codes using the experimental results of the in-pile Phebus fission product tests (FPTs). It is shown that the integral codes are good in predicting both the hydrogen release and the total release of volatile fission products from the bundle. It is also shown that the commonly used fission product transport codes overestimate the deposited aerosol mass in the Phebus steam generator. However, by using an improved model for the thermophoretic aerosol particle deposition, it has been possible to reproduce the aerosol mass deposited in the steam generator more accurately. The containment analyses carried out with both lumped-parameter and multidimensional computational fluid dynamics codes showed that the measured thermal-hydraulic data are accurately reproduced. The aerosol behavior in the containment estimated from the lumped-parameter codes corresponded satisfactorily to the experimental data. The iodine chemistry codes highlighted the substantial role of silver released from the degraded absorber rod (Ag-In-Cd), as it was observed experimentally; however, the temporal dependence of the gaseous iodine concentration in the containment atmosphere was poorly calculated. There are plans to improve the modeling in order to reproduce better the fission product release from the bundle, the fission product transport in the primary circuit duct, and the gas phase chemistry in the containment, with particular emphasis on gaseous iodine species. Further plans include the analysis of Phebus FPT3, which was the last in the series of Phebus tests, with its boron-carbide control rod.
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Résumé/Abstract During some pressurized water reactor risk-dominant sequences, most of the radioactivity is discharged at very high velocities into nearly saturated pools. An experimental plan for pool scrubbing and its associated... more
Résumé/Abstract During some pressurized water reactor risk-dominant sequences, most of the radioactivity is discharged at very high velocities into nearly saturated pools. An experimental plan for pool scrubbing and its associated hydrodynamics under ...
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Driving forces of passive cooling systems of advanced reactor containments are substantially weaker than those brought in by active systems of operating power plants. This fact along with the new geometries being used suggest the need... more
Driving forces of passive cooling systems of advanced reactor containments are substantially weaker than those brought in by active systems of operating power plants. This fact along with the new geometries being used suggest the need either to develop new reliable simulation techniques or to adapt and validate traditional approaches. Suitability of the heat-mass transfer analogy for this purpose is investigated based on previous authors' experience. Major analogy drawbacks are identified and overcome by supplementing it with analytically derived factors. By comparing against experimental data available, the heat-mass transfer analogy is demonstrated to be a sound, configuration-independent, and accurate-enough theoretical approximation.
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A mechanistic model is presented to predict the steam condensation on containment finned tubes in the presence of noncondensables (NCs). The total thermal resistance from bulk gas to coolant is formulated as a parallel combination of the... more
A mechanistic model is presented to predict the steam condensation on containment finned tubes in the presence of noncondensables (NCs). The total thermal resistance from bulk gas to coolant is formulated as a parallel combination of the convective and condensation gas resistances coupled in series to those of the condensate layer, the wall, and the coolant.The condensate layer thermal resistance
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NUREG-1465 was a major change to the preceding figures defining in-containment source term. Since then, the most important research venture in the arena of severe accidents has been the PHEBUS-FP project. Experimental data and... more
NUREG-1465 was a major change to the preceding figures defining in-containment source term. Since then, the most important research venture in the arena of severe accidents has been the PHEBUS-FP project. Experimental data and interpretations brought in along the course of the project have highlighted similarities and discrepancies with those insights given in the NUREG-1465.This paper sets comparisons between NUREG-1465 and PHEBUS-FP in three key aspects: the release of radionuclides into containment, the in-containment aerosol behaviour and, finally, iodine chemical behaviour in the containment. The experimental basis of discussions is the FPT0, FPT1, FPT2 and FPT3 series, although the latter cannot be openly addressed yet. Similarities have been found regarding qualitative gap and early in-vessel releases, quantitative net release of noble gases and iodine releases, dominance of sedimentation as natural removal mechanism for in-containment aerosols, etc. Nonetheless, PHEBUS-FP data have also drawn attention to major discrepancies with respect to NUREG-1465. Examples are cesium and tellurium releases and possible massive iodine release under specific conditions. But, in addition, PHEBUS-FP has brought new insights, such as potential formation of in-sump iodine precipitates or the need of revisiting NUREG-1465 element grouping.
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ABSTRACT The transport phenomenon between a fluid in movement and a wall is strongly affected by the permeability of the wall. The application of a correction factor standing for the transpiration effect will be required whenever a heat... more
ABSTRACT The transport phenomenon between a fluid in movement and a wall is strongly affected by the permeability of the wall. The application of a correction factor standing for the transpiration effect will be required whenever a heat transfer model is based either on the use of heat, mass or momentum analogies or on the use of empirical correlations for the computation of the heat transfer coefficient.The suction factor commonly used when solving as a function of either mass or molar fractions is called the Bird suction factor. The validity of this factor rests on the hypothesis of the film theory or Couette flow.This paper reviews the Bird suction factor in laminar regime, extending the analysis to turbulent flow conditions and finding thereby that Bird's equation can overestimate the suction factor under turbulent condensation conditions in the gas phase.Finally, an alternative formulation for the suction factor under turbulent condensation conditions has been proposed and compared with Bird's original formulation. In doing this, both data and models developed by other authors and the UW-Madison test facility database have been used.The results show the suitability of the alternative formulation when calculating the condensation rate in turbulent natural circulation scenarios, whereas Bird's formulation seems to be more appropriate for laminar regimes.
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The Fukushima accidents highlighted that both the in-depth understanding of such sequences and the development or improvement of adequate Severe Accident Management (SAM) measures are essential in order to further increase the safety of... more
The Fukushima accidents highlighted that both the in-depth understanding of such sequences and the development or improvement of adequate Severe Accident Management (SAM) measures are essential in order to further increase the safety of the nuclear power plants operated in Europe. To support this effort, the CESAM (Code for European Severe Accident Management) R&D project, coordinated by GRS, started in April 2013 for 4 years in the 7th EC Framework Programme of research and development of the European Commission. It gathers 18 partners from 12 countries: IRSN, AREVA NP SAS and EDF (France), GRS, KIT, USTUTT and RUB (Germany), CIEMAT (Spain), ENEA (Italy), VUJE and IVS (Slovakia), LEI (Lithuania), NUBIKI (Hungary), INRNE (Bulgaria), JSI (Slovenia), VTT (Finland), PSI (Switzerland), BARC (India) plus the European Commission Joint Research Center (JRC). The CESAM project focuses on the improvement of the ASTEC (Accident Source Term Evaluation Code) computer code. ASTEC,, jointly devel...
Summary The Phebus-FP Project has become a fundamental reference in the area of severe accidents. Aimed at investigating key aspects of the behaviour of fission products under prototypical accident conditions, the tests have provided... more
Summary The Phebus-FP Project has become a fundamental reference in the area of severe accidents. Aimed at investigating key aspects of the behaviour of fission products under prototypical accident conditions, the tests have provided essential insights into iodine transport through the primary circuit and the chemistry of iodine in the containment. The current paper presents a preliminary interpretation of the
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Development of HTRs requires the performance of a thorough safety study, which includes accident analyses. Confinement building performance is a key element of the system since the behaviour of aerosol and attached fission products within... more
Development of HTRs requires the performance of a thorough safety study, which includes accident analyses. Confinement building performance is a key element of the system since the behaviour of aerosol and attached fission products within the building is of an utmost relevance in terms of the potential source term to the environment. This paper explores the available simulation capabilities (ASTEC and CONTAIN codes) and illustrates the performance of a postulated HTR vented confinement under prototypical accident conditions by a scoping study based on two accident sequences characterized by Helium Pressure Boundary breaches, a small and a large break. The results obtained indicate that both codes predict very similar thermal-hydraulic responses of the confinement both in magnitude and timing. As for the aerosol behaviour, both codes predict that most of the inventory coming into the confinement is eventually depleted on the walls and only about 1% of the aerosol dust is released to ...
The current trend in nuclear industry to extend the burnup limits up to high burnup requires the analysis of the phenomenology related to the nuclear fuel, specifically the diffusion and fission gas release (FGR) related to this... more
The current trend in nuclear industry to extend the burnup limits up to high burnup requires the analysis of the phenomenology related to the nuclear fuel, specifically the diffusion and fission gas release (FGR) related to this phenomenon plays an important role. In this paper, the diffusion of stable fission gases (xenon and krypton) in nuclear fuel UO2 is addressed through the predictions for FGR to rod void volumes obtained with FRAPCON-3 fuel performance code. The theoretical base of diffusion model in FRAPCON-3 code is shown and some modifications are proposed, such as the removing of empirical correlations not related to diffusion phenomenon and fitting parameters included in the model. Besides, the resolution process in the proximities of grain boundaries is considered in a different way, and the grain growth mechanism from a specific temperature threshold is implemented into the code. The database applied for evaluation is presented and the results with the original and mod...
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Iodine Chemistry is one of the areas of top interest in the field of nuclear power plants (NPP) severe accidents studies. The strong radiological impact of iodine on man health and environment, mostly through its isotope I-131, has made... more
Iodine Chemistry is one of the areas of top interest in the field of nuclear power plants (NPP) severe accidents studies. The strong radiological impact of iodine on man health and environment, mostly through its isotope I-131, has made it a key point to get an accurate prediction of the potential iodine release from the NPP containment to the environment in the low probable event of an accident leading to core melt. Released from the fuel as a gaseous form, iodine enters the containment in gaseous or particulate form and undergoes deposition processes that eventually take it to the containment surfaces and sump. Once in the sump, iodine, when present as soluble compounds, get dissolved as non volatile iodide (I-). Nonetheless, in the presence of radiation and particularly in acidic sumps, iodine can be oxidized to volatile forms such as molecular iodine (I2) and can escape from the sump to the containment atmosphere (sump radiolysis process), thus increasing its potential contribut...
ABSTRACT y 90 investigadores de 13 instituciones 1 2 UPM 3 UNED 4 CIMNE 5 UPC 6 7 8 9 10 CONSOLIDER TECNO_FUS propone el lanzamiento de un nuevo Programa de Tecnología de Fusión en España. TECNO_FUS es un programa orientado que integra... more
ABSTRACT y 90 investigadores de 13 instituciones 1 2 UPM 3 UNED 4 CIMNE 5 UPC 6 7 8 9 10 CONSOLIDER TECNO_FUS propone el lanzamiento de un nuevo Programa de Tecnología de Fusión en España. TECNO_FUS es un programa orientado que integra interactivamente áreas clave de la tecnología de fusión. Las actividades se articulan alrededor del desarrollo de un concepto de envoltura regeneradora y sus sistemas auxiliares "de planta". Atendiendo a sus requisitos funcionales como componente: integridad estructural, blindaje de la radiación, eficiencia en la extracción de potencia y garantías de regeneración de combustible; la envoltura regeneradora es probablemente el componente más complejo desarrollado hoy por la tecnología energética. Los sistemas envoltura son clave en reactores de producción de potencia por fusión y sus desarrollos cruciales en el camino de la fusión hacia la producción energética masiva. La propuesta CONSOLIDER TECNO_FUS responde al objetivo estratégico del programa de fusión español de alcanzar capacidades de diseño de un reactor de potencia (DEMO) en la próxima década.
Summary The 5th FWP EURSAFE project highlighted iodine chemistry in the containment as one of the issues requiring further research in order to reduce source term uncertainties. Consequently, a series of studies was launched in the 6th... more
Summary The 5th FWP EURSAFE project highlighted iodine chemistry in the containment as one of the issues requiring further research in order to reduce source term uncertainties. Consequently, a series of studies was launched in the 6th FWP SARNET project aimed at improving the predictability of iodine behaviour during severe accidents via a better understanding of the complex chemical phenomena
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ABSTRACT Fusion energy is one of the most promising solutions to the world energy supply. This paper presents an exploratory analysis of the suitability of supercritical CO2 Brayton power cycles (S-CO2) for low-temperature divertor fusion... more
ABSTRACT Fusion energy is one of the most promising solutions to the world energy supply. This paper presents an exploratory analysis of the suitability of supercritical CO2 Brayton power cycles (S-CO2) for low-temperature divertor fusion reactors cooled by helium (as defined by EFDA). Integration of three thermal sources (i.e., blanket, divertor and vacuum vessel) has been studied through proposing and analyzing a number of alternative layouts, achieving an improvement on power production higher than 5% over the baseline case, which entails to a gross efficiency (before self-consumptions) higher than 42%. In spite of this achievement, the assessment of power consumption for the circulating heat transfer fluids results in a penalty of 20% in the electricity production. Once the most suitable layout has been selected an optimization process has been conducted to adjust the key parameters to balance performance and size, achieving an electrical efficiency (electricity without taking into account auxiliary consumptions due to operation of the fusion reactor) higher than 33% and a reduction in overall size of heat exchangers of 1/3. Some relevant conclusions can be drawn from the present work: the potential of S-CO2 cycles as suitable converters of thermal energy to power in fusion reactors; the significance of a suitable integration of thermal sources to maximize power output; the high penalty of pumping power; and the convenience of identifying the key components of the layout as a way to optimize the whole cycle performance.