Simulation of Hydrogen Distribution due to In-Vessel Severe Accident in WWER-1000 NPP Containment: A Comparison of CONTAIN and MELCOR Codes Results

2018 ◽  
Author(s):  
Omid Noorikalkhoran ◽  
Massimiliano Gei
Keyword(s):  
Severe Accident ◽  
Second Step ◽  
Hydrogen Distribution ◽  
Short Term ◽  
Long Time ◽  
Design Basis Accident ◽  
Safety Features ◽  
Design Pressure ◽  
Good Agreement

During a severe accident or Beyond Design Basis Accident (BDBA), the reaction of water with zirconium alloy as fuel clad, radiolysis of water, molten corium-concrete interaction (MCCI) and post-accident corrosion can generate a source of hydrogen. In the present work, hydrogen distribution due to in-vessel reaction (between zircaloy and steam) has been simulated inside a WWER-1000 reactor containment. In the first step, the thermal hydraulic parameters of containment have been simulated for a DECL (Double Ended Cold Leg) accident (DBA phase) in both short and long time and the effects of spray as Engineering Safety Features (ESFs) on mitigating the parameters have been studied. In the second step, it has been assumed that the accident developed into an in-vessel core melting accident. While in pre-phase of core melting (severe accident phase), hydrogen will be produced as a result of zircaloy and steam reaction (BDBA phase), the hydrogen distribution has been simulated for 23 cells inside the reactor containment by using CONTAIN 2.0 (Best estimate code) and MELCOR 1.8.6 codes. Finally, the results have been compared to FSAR results. As it can be seen from the comparisons, both CONTAIN and MELCOR codes can predict the results in good agreement with FSAR (ANGAR code) results. CONTAIN shows peak pressure around 0.36 MPa in short-term and this amount is about 0.38 and 0.4 MPa for MELCOR and ANGAR (FSAR) results respectively. All these values are under design pressure that is around 0.46 MPa. Cell 20 has the maximum mole fraction of hydrogen in long-term about 9.5% while the maximum amount of hydrogen takes place in cell 22. The differences between the results of codes are because of different equations, Models, Numerical methods and assumptions that have been considered by the codes. The simulated Hydrogen Distribution Map (HDM) can be used for upgrading the location of HCAV systems and Hydrogen Mitigator features (like the recombiners and ignitors) inside the containment to reduce the risk of hydrogen explosion.

scholarly journals Methods of long-term and short-term adaptation for biometric image of keystroke dynamics

2021 ◽  
Vol 7 (3D) ◽  
pp. 450-457
Author(s):  
Dmitry V. Pashchenko ◽  
Dmitry A. Trokoz ◽  
Alexey I. Martyshkin ◽  
Elena A. Balzannikova
Keyword(s):  
Working Capacity ◽  
Keystroke Dynamics ◽  
Short Term ◽  
User Identification ◽  
New Device ◽  
Short Term Adaptation ◽  
Long Time

This article discusses one of the main problems of user identification by keyboard handwriting - short-term changes in the keystroke dynamics of users in connection with its psychophysical state, as well as changes over a long time associated with the formation of keystroke dynamics by a new user or when switching to a new device. A method for determining the phase of working capacity by the time characteristics of the keystroke dynamics is proposed.

A Canonical Microfunction for Learning Perceptual Invariances

Perception ◽  
1996 ◽  
Vol 25 (2) ◽  
pp. 207-220 ◽  
Author(s):  
James V Stone
Keyword(s):  
Model Neuron ◽  
Learning Rule ◽  
Image Sequences ◽  
Weight Changes ◽  
Short Term ◽  
Stereo Disparity ◽  
Random Dot Stereograms ◽  
Long Time ◽  
Generic Strategy

An unsupervised method is presented which permits a set of model neurons, or a microcircuit, to learn low-level vision tasks, such as the extraction of surface depth. Each microcircuit implements a simple, generic strategy which is based on a key assumption: perceptually salient visual invariances, such as surface depth, vary smoothly over time. In the process of learning to extract smoothly varying invariances, each microcircuit maximises a microfunction. This is achieved by means of a learning rule which maximises the long-term variance of the state of a model neuron and simultaneously minimises its short-term variance. The learning rule involves a linear combination of anti-Hebbian and Hebbian weight changes, over short and long time scales, respectively. The method is demonstrated on a hyperacuity task: estimating subpixel stereo disparity from a temporal sequence of random-dot stereograms. After learning, the microcircuit generalises, without additional learning, to previously unseen image sequences. It is proposed that the approach adopted here may be used to define a canonical microfunction, which can be used to learn many perceptually salient invariances.

scholarly journals Study of hydrodynamics performance of a multi-venturi filtering system for BWR severe accident venting strategies

2020 ◽  
Vol 35 (1) ◽  
pp. 16-23
Author(s):  
Alejandro Reyes-Garcia ◽  
Eduardo Sainz-Mejia ◽  
Javier Ortiz-Villafuerte ◽  
Javier Palacios-Hernandez ◽  
Roberto Lopez-Solis
Keyword(s):  
Pressure Drop ◽  
Mass Flow ◽  
Reference Model ◽  
Geometrical Model ◽  
Severe Accident ◽  
Cfd Models ◽  
Station Blackout ◽  
Experimental Values ◽  
Good Agreement

The aim of this project was to determine the capacity of a multi-venturi scrubber filtering system to cope with vented gas mass-flow rate coming from a BWR Mark II primary containment during a long-term station blackout. The multi-venturi filtering system CFD models were developed in the environment of the open source platforms SALOME and OpenFoam. The first geometrical model was created based on the dimensions of a well-known experimental setup, and the results of the pressure drop along the streamwise co-ordinate showed a maximum difference of 10 % in relation to the experimental values for different cases of liquid to gas mass ratios. Then a full scale multi-venturi model was developed. To study the performance of this system during conditions expected in a severe accident, a gas mixture similar to that occurring in a BWR Mark II containment at venting pressure was used as inlet gas. The gas mass-flow that can be cleansed by individual venturis and the pressure required to activate those venturis were computed. The pressure drop profiles in each sector were also determined as the function of different liquid loadings. The results showed good agreement with the capacity of the design taken as the reference model.

Influence of Whipping on Long-term Vertical Bending Moment

2004 ◽  
Vol 48 (04) ◽  
pp. 261-272
Author(s):  
Gro Sagli Baarholm ◽  
Jørgen Juncher Jensen
Keyword(s):  
Nonlinear Response ◽  
Extreme Values ◽  
Bending Moment ◽  
Sea Waves ◽  
Short Term ◽  
Strip Theory ◽  
Long Time ◽  
Wave Induced ◽  
Vertical Bending Moment

This paper is concerned with estimating the response value corresponding to a long return period, say 20 years. Time domain simulation is required to obtain the nonlinear response, and long time series are required to limit the statistical uncertainty in the simulations. It is crucial to introduce ways to improve the efficiency in the calculation. A method to determine the long-term extremes by considering only a few short-term sea states is applied. Long-term extreme values are estimated using a set of sea states that have a certain probability of occurrence, known as the contour line approach. Effect of whipping is included by assuming that the whipping and wave-induced responses are independent, but the effect of correlation of the long-term extreme value is also studied. Numerical calculations are performed using a nonlinear, hydroelastic strip theory as suggested by Xia et al (1998). Results are presented for the S-175 containership (ITTC 1983) in head sea waves. The analysis shows that whipping increases the vertical bending moment and that the correlation is significant.

Short-term stress for long-lasting otolith morphology — brief embryological stress disturbance can reorient otolith ontogenetic trajectory

2018 ◽  
Vol 75 (10) ◽  
pp. 1713-1722 ◽  
Author(s):  
Matthias Vignon
Keyword(s):  
Environmental Conditions ◽  
Salmo Trutta ◽  
Short Term ◽  
Otolith Shape ◽  
Fisheries Resources ◽  
Otolith Morphology ◽  
Ontogenetic Trajectory ◽  
Brown Trout Salmo Trutta ◽  
Long Time

Long-term plasticity of otolith shape has become a unifying principle to use morphological differences as indicator of environmental conditions. Contrary to the longstanding paradigmatic view that otolith shape can only reflect residency in particular environmental conditions over long time periods, data emphasize that otolith ontogenetic trajectory may be reoriented in case of short-term episodes of environmental disturbance during early lifetime. Using geometric morphometrics, discrimination was posible in absence of growth-related differences between control and brown trout (Salmo trutta Linnaeus, 1758) that have experienced brief thermal stress prior to their emergence but have grown in similar conditions (i.e., cohabiting within the same aquarium) during 6 months. Data emphasize that brief stress during key developmental periods can durably influence ontogenetic trajectories, subsequent otolith development, and can consequently change otolith morphology in juveniles. Therefore, differences in shape between groups of fish may not be exclusively indicative of long-time residency in contrasted and (or) separated habitats as it is generally assumed. Moving beyond long-term assumptions is fundamental if otolith shape is to be used as an effective tool for management of fisheries resources in the future.

Technical Challenges Facing Regulators–Assessment of Long-Term Materials Performance

1987 ◽  
Vol 112 ◽  
Author(s):  
Kenneth W. Stephens
Keyword(s):  
Real Time ◽  
Waste Disposal ◽  
Time Frame ◽  
High Level Waste ◽  
Short Term ◽  
Long Time ◽  
Computer Codes ◽  
High Level ◽  
Term Data

AbstractFor a number of years, nuclear regulators have grappled with difficult questions such as: “How safe is safe enough?” Such issues take on new dimensions in the long time-frame of high-level waste disposal.Many of the challenges facing regulators involve assessment of long-term materials performance. Because real-time experiments cannot be conducted, it is necessary to rely extensively on modeling. This raises issues regarding the extent to which long-term extrapolations of short-term data are justified, the question of how closely models must represent reality to be trusted, and practical matters such as methods for validating unique computer codes.Issues such as these illustrate how regulators must make decisions in a climate of uncertainty. Methods used by non-technical disciplines to make decisions under uncertainty have been examined and offer solutions for regulators and licensees alike.

scholarly journals Estimating survival in echinoid populations

Zoosymposia ◽  
2019 ◽  
Vol 15 (1) ◽  
pp. 23-32 ◽  
Author(s):  
THOMAS A. EBERT ◽  
JOSÉ CARLOS HERNÁNDEZ ◽  
SABRINA CLEMENTE
Keyword(s):  
Size Structure ◽  
Short Term ◽  
Term Study ◽  
Basic Part ◽  
Purple Sea Urchin ◽  
Stationary Structure ◽  
Long Term Study ◽  
Long Time ◽  
New Recruits

Estimating survival rate is a basic part of population studies. Generally it is assumed that populations being studied are both stable and stationary. This probably is seldom the case although as a long-term average populations may persist at a mean density. Estimating survival in short-term studies may fail to capture average rates. A long-term study of the purple sea urchin Strongylocentrotus purpuratus at Sunset Bay, OR, USA from 1964–2009 is used to demonstrate methods for estimating survival based on the coefficient of variation of size distributions, the fraction of new recruits in a population, means of size data coupled with estimates of growth, and a method that uses rates of flow through size categories. A short-term study of just a few years may by chance sample when an unusual recruitment event drives a population far from stationary structure and so distorts the estimate of mean survival. The best solution, as shown for S. purpuratus, is a long time series but in advance it cannot be determined how long this should be. If a study of three years shows no substantial change in population size structure it may be reasonable to accept estimates of survival.

How Should We Combine Long and Short Term Wave Height Distributions?

2008 ◽  
Author(s):  
George Z. Forristall
Keyword(s):  
Time Series ◽  
Extreme Value Distribution ◽  
Ocean Engineering ◽  
Short Term ◽  
Method Of Calculation ◽  
Individual Wave ◽  
Long Time ◽  
Wave Heights ◽  
The Individual

Estimating the maximum wave or crest height that will occur in a long return interval is one of the fundamental problems for ocean engineers. Long time series of individual wave heights are not available. The calculations must start with measured or hindcast time series of significant wave heights. An extreme value distribution is fit to that data. The resulting long term distribution is then combined with a short term distribution for the individual heights. This study is concerned with finding the most accurate methods for that calculation. The basic tool is the Borgman integral, but it has been applied in many different ways. Theoretical derivations do not clearly indicate which method is most accurate, and time series of measurements long enough for accurate tests do not exist. These problems were circumvented in this study by constructing very long simulated time series with known distributions. Both initial value and storm based methods were tested. The correct method of calculation depends on what question is being asked. The distribution of the maximum wave heights in a six hour interval is different than the distribution of the maxima of all of the waves. The distribution of the maxima in a storm is different than the distribution of the maxima in an interval. We believe that the finding the maximum in a storm is the most appropriate question for ocean engineering design. The Tromans and Vanderschuren (1995, Proc. Offshore Tech. Conf., OTC 7683) method accurately matches the results from our storm simulations.

Prediction of Hydrogen Distribution Under Severe Accident Conditions With CFD and Lumped Parameter Codes

2012 ◽  
Author(s):  
Tobias Szabó ◽  
Stefan Benz ◽  
Frank Kretzschmar ◽  
Peter Royl ◽  
Thomas Jordan
Keyword(s):  
Source Term ◽  
Severe Accident ◽  
Test Bed ◽  
Hydrogen Distribution ◽  
Water Steam ◽  
Lumped Parameter ◽  
Accident Conditions ◽  
Energy Balances ◽  
Mass And Energy Balances ◽  
Good Agreement

In case of a severe accident, the containment is the ultimate barrier to the environment. Therefore, reliable simulations tools for containment thermal hydraulics, including hydrogen distribution are indispensable. We simulated the behavior of the containment atmosphere under severe accident conditions with a postulated source term of water, steam and hydrogen. We used a detailed 3D CFD code (GASFLOW) and a lumped parameter code (MELCOR) in order to compare and assess their modeling capabilities. A simplified generic containment including all important components was used as a test bed. We analyzed the calculated pressure histories, mass and energy balances, convective flow as well as steam and hydrogen distributions. Integral values were modeled in good agreement by both codes. The overall flow was reasonably predicted. However we observed discrepancies in the calculated steam and hydrogen concentrations.

Study on Characteristics of Water Waves in Bohai Sea Using SWAN Model

2014 ◽  
Vol 522-524 ◽  
pp. 983-989
Author(s):  
Dao Sheng Wang ◽  
Xiang Cui Lv ◽  
De Kui Yuan
Keyword(s):  
Wave Height ◽  
Water Waves ◽  
Bohai Sea ◽  
Measured Data ◽  
Wave Direction ◽  
Short Term ◽  
The Bohai Sea ◽  
Good Agreement ◽  
Term Field

The SWAN (Simulating WAves Nearshore) model was applied to study the characteristics of water waves in the Bohai Sea. The model was calibrated against both short-term and long-term field measured data from six different stations in the Bohai Sea and the computational results are in good agreement with the measured data. Then the wave process during 1999 to 2009 in the Bohai Sea was simulated using the calibrated model. The wave characteristics such as significant wave height, average period, dominant wave direction and their seasonal variations were analyzed based on the simulated results. The distributions of wave height and wave period are similar to those of the previous studies, but the wave height is slightly smaller than that given by other researchers.

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