In response to the accident at the Fukushima Daiichi nuclear power station in Japan, the U.S. Nuc... more In response to the accident at the Fukushima Daiichi nuclear power station in Japan, the U.S. Nuclear Regulatory Commission and U.S. Department of Energy agreed to jointly sponsor an accident reconstruction study as a means of assessing the severe accident modeling capability of the MELCOR code. Objectives of the project included reconstruction of the accident progressions using computer models and accident data, and validation of the MELCOR code and the Fukushima models against plant data. A MELCOR 2.1 model of the Fukushima Daiichi Unit 3 reactor is developed using plant-specific information and accident-specific boundary conditions, which involve considerable uncertainty due to the inherent nature of severe accidents. Publicly available thermal-hydraulic data and radioactivity release estimates have evolved significantly since the accidents. Such data are expected to continually change as the reactors are decommissioned and more measurements are performed. The MELCOR simulations in this work primarily use boundary conditions that are based on available plant data as of May 2012.
This paper provides an overview of the uncertainty analysis for the accident progression, radiolo... more This paper provides an overview of the uncertainty analysis for the accident progression, radiological releases, and offsite consequences for the State-of-the-Art Reactor Consequence Analyses (SOARCA) unmitigated long-term station blackout accident scenario at the Peach Bottom Atomic Power Station. The SOARCA project (NUREG-1935) estimated the outcomes of postulated severe accident scenarios which could result in release of radioactive material from a nuclear power plant into the environment. The SOARCA model was based on best practices used to estimate offsite consequences of important classes of events. SOARCA coupled the deterministic 'best estimate' modeling of accident progression (i.e., reactor and containment thermal-hydraulic response and fission product transport), embodied in the MELCOR code with modeling of offsite consequences in MACCS2. This uncertainty analysis presents the results of an integrated analysis of epistemic parameter uncertainty associated with the accident progression and offsite consequence modeling. This uncertainty analysis supported the overall conclusions of the SOARCA project and provided some new insights.
ABSTRACT The MELPROG computer code is being developed to provide mechanistic treatment of Light W... more ABSTRACT The MELPROG computer code is being developed to provide mechanistic treatment of Light Water Reactor (LWR) accidents from accident initiation through vessel failure. This paper describes a two-dimensional (r-z) debris meltdown model that is being developed for use in the MELPROG code and discusses validation experiments. Of interest to this study is melt progression in particle beds that can form in both the reactor core and the lower plenum during severe LWR accidents. Key results are (1) a dense metallic crust is created near the bottom of the bed as molten materials flow downward and freeze; (2) liquid accumulates above the blockage as solid continues to melt and if Zirconium is present, the pool grows rapidly as the molten Zr dissolves both UOâ and ZrOâ particles; (3a) if the melt wets the solid, a fraction of the melt flows radially outward under the action of capillary forces and freezes near the radial boundary; and (3b) in a nonwetting system, all of the melt flows into the bottom of the bed. Solutions are qualitatively similar to the post-accident configuration of the Three-Mile Island (TMI-2) core. When the models discussed here are implemented in the MELPROG code, we will be able to conduct a very detailed TMI-2 calculation.
The MELPROG code is being developed jointly at Sandia National Laboratories and Los Alamos Nation... more The MELPROG code is being developed jointly at Sandia National Laboratories and Los Alamos National Laboratory to provide the US Nuclear Regulatory Commission (USNRC) with an integrated analysis model for light water reactor (LWR) severe fuel damage (SFD) accidents. MELPROG is a mechanistic code, based upon detailed physics models, that will calculate the progression of a core uncovered accident including the multidimensional thermal hydraulics, core degradation, loss of geometry, melting of the core rods, debris formation, radionuclide release and transport, attack of the support structure, core slumping, melt-water interactions, and vessel failure. Additionally MELPROG can be coupled to the TRAC code to treat fission product transport and the thermal hydraulics of the reactor coolant system (RCS). As part of this development effort, the phenomenological modelling in the code is undergoing extensive assessment. This assessment effort involves comparing the data from experimental programs with code predictions to validate the models used and to identify areas of needed model improvement. An important component of this effort is the assessment of the models used to describe the fuel rod heat-up, melting, and relocation phases of an uncovered accident. The Damaged Fuel (DF) experiments are examples of experiments being performed to address these issues. This paper describes a posttest MELPROG analysis of the first of these tests. 6 refs., 9 figs., 2 tabs.
IEEE Transactions on Industry Applications, Nov 1, 1984
Experimental data are presented on the electrical charge acquired by near-micrometer sized aeroso... more Experimental data are presented on the electrical charge acquired by near-micrometer sized aerosol particles exposed to bipolar ions. Aerosols ranging in size from 0.31 to 1.09 itm in diameter were atomized from monodisperse polystyrene latex hydrosols and exposed to bipolar air ions in a laminar flow charging apparatus. Particle charge was determined by an integral mobility analysis technique. Results demonstrating the charging time dependence (expressed through the parameter A+N+t), the particle size dependence, and the charging electric field strength dependence are presented for ratios of positive to negative ion conductivity between one and infinity (unipolar positive). The range of IA+N+t for the time dependent data was from approximately 4.0 x 1010 to 6.0 x 1012 kV-I m-', with the charging field strength at 50 kV m-'. The + NIt product was maintained at 6.08 x 10" kV-'m -' for the particle size dependent and field strength dependent tests, where for the latter, the electric field strength was varied from 25 to 300 kV m'. The charging electric field strength for the size dependent data was 300 kV m-'. Charge measurements are compared to predictions ofclassical continuum field theory and to an empirical superposition calculation in which the prediction of charge from continuum diffusion theory is simply added to that from field theory. Field theory predictions fall significantly below measurements; however, the empirical superposition calculations show good agreement with experiment. It is concluded that the empirical superposition calculation may be a practical alternative to rigorous theory for bipolar charging which includes the simultaneous effects of ionic diffusion and ion electrical transport in the presence of a uniform applied electric field.
In response to the accident at the Fukushima Daiichi nuclear power station in Japan, the U.S. Nuc... more In response to the accident at the Fukushima Daiichi nuclear power station in Japan, the U.S. Nuclear Regulatory Commission and U.S. Department of Energy agreed to jointly sponsor an accident reconstruction study as a means of assessing the severe accident modeling capability of the MELCOR code. Objectives of the project included reconstruction of the accident progressions using computer models and accident data, and validation of the MELCOR code and the Fukushima models against plant data. A MELCOR 2.1 model of the Fukushima Daiichi Unit 3 reactor is developed using plant-specific information and accident-specific boundary conditions, which involve considerable uncertainty due to the inherent nature of severe accidents. Publicly available thermal-hydraulic data and radioactivity release estimates have evolved significantly since the accidents. Such data are expected to continually change as the reactors are decommissioned and more measurements are performed. The MELCOR simulations in this work primarily use boundary conditions that are based on available plant data as of May 2012.
This paper provides an overview of the uncertainty analysis for the accident progression, radiolo... more This paper provides an overview of the uncertainty analysis for the accident progression, radiological releases, and offsite consequences for the State-of-the-Art Reactor Consequence Analyses (SOARCA) unmitigated long-term station blackout accident scenario at the Peach Bottom Atomic Power Station. The SOARCA project (NUREG-1935) estimated the outcomes of postulated severe accident scenarios which could result in release of radioactive material from a nuclear power plant into the environment. The SOARCA model was based on best practices used to estimate offsite consequences of important classes of events. SOARCA coupled the deterministic 'best estimate' modeling of accident progression (i.e., reactor and containment thermal-hydraulic response and fission product transport), embodied in the MELCOR code with modeling of offsite consequences in MACCS2. This uncertainty analysis presents the results of an integrated analysis of epistemic parameter uncertainty associated with the accident progression and offsite consequence modeling. This uncertainty analysis supported the overall conclusions of the SOARCA project and provided some new insights.
ABSTRACT The MELPROG computer code is being developed to provide mechanistic treatment of Light W... more ABSTRACT The MELPROG computer code is being developed to provide mechanistic treatment of Light Water Reactor (LWR) accidents from accident initiation through vessel failure. This paper describes a two-dimensional (r-z) debris meltdown model that is being developed for use in the MELPROG code and discusses validation experiments. Of interest to this study is melt progression in particle beds that can form in both the reactor core and the lower plenum during severe LWR accidents. Key results are (1) a dense metallic crust is created near the bottom of the bed as molten materials flow downward and freeze; (2) liquid accumulates above the blockage as solid continues to melt and if Zirconium is present, the pool grows rapidly as the molten Zr dissolves both UOâ and ZrOâ particles; (3a) if the melt wets the solid, a fraction of the melt flows radially outward under the action of capillary forces and freezes near the radial boundary; and (3b) in a nonwetting system, all of the melt flows into the bottom of the bed. Solutions are qualitatively similar to the post-accident configuration of the Three-Mile Island (TMI-2) core. When the models discussed here are implemented in the MELPROG code, we will be able to conduct a very detailed TMI-2 calculation.
The MELPROG code is being developed jointly at Sandia National Laboratories and Los Alamos Nation... more The MELPROG code is being developed jointly at Sandia National Laboratories and Los Alamos National Laboratory to provide the US Nuclear Regulatory Commission (USNRC) with an integrated analysis model for light water reactor (LWR) severe fuel damage (SFD) accidents. MELPROG is a mechanistic code, based upon detailed physics models, that will calculate the progression of a core uncovered accident including the multidimensional thermal hydraulics, core degradation, loss of geometry, melting of the core rods, debris formation, radionuclide release and transport, attack of the support structure, core slumping, melt-water interactions, and vessel failure. Additionally MELPROG can be coupled to the TRAC code to treat fission product transport and the thermal hydraulics of the reactor coolant system (RCS). As part of this development effort, the phenomenological modelling in the code is undergoing extensive assessment. This assessment effort involves comparing the data from experimental programs with code predictions to validate the models used and to identify areas of needed model improvement. An important component of this effort is the assessment of the models used to describe the fuel rod heat-up, melting, and relocation phases of an uncovered accident. The Damaged Fuel (DF) experiments are examples of experiments being performed to address these issues. This paper describes a posttest MELPROG analysis of the first of these tests. 6 refs., 9 figs., 2 tabs.
IEEE Transactions on Industry Applications, Nov 1, 1984
Experimental data are presented on the electrical charge acquired by near-micrometer sized aeroso... more Experimental data are presented on the electrical charge acquired by near-micrometer sized aerosol particles exposed to bipolar ions. Aerosols ranging in size from 0.31 to 1.09 itm in diameter were atomized from monodisperse polystyrene latex hydrosols and exposed to bipolar air ions in a laminar flow charging apparatus. Particle charge was determined by an integral mobility analysis technique. Results demonstrating the charging time dependence (expressed through the parameter A+N+t), the particle size dependence, and the charging electric field strength dependence are presented for ratios of positive to negative ion conductivity between one and infinity (unipolar positive). The range of IA+N+t for the time dependent data was from approximately 4.0 x 1010 to 6.0 x 1012 kV-I m-', with the charging field strength at 50 kV m-'. The + NIt product was maintained at 6.08 x 10" kV-'m -' for the particle size dependent and field strength dependent tests, where for the latter, the electric field strength was varied from 25 to 300 kV m'. The charging electric field strength for the size dependent data was 300 kV m-'. Charge measurements are compared to predictions ofclassical continuum field theory and to an empirical superposition calculation in which the prediction of charge from continuum diffusion theory is simply added to that from field theory. Field theory predictions fall significantly below measurements; however, the empirical superposition calculations show good agreement with experiment. It is concluded that the empirical superposition calculation may be a practical alternative to rigorous theory for bipolar charging which includes the simultaneous effects of ionic diffusion and ion electrical transport in the presence of a uniform applied electric field.
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Papers by Randall Gauntt