Post test calculations of a severe accident experiment for VVER-440 reactors by the ATHLET code

Kerntechnik ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. 362-370
Author(s):  
H. György ◽  
I. Trosztel
Keyword(s):  
Severe Accident ◽  
Post Test

COCOSYS and ASTEC Analyses of Iodine Multi-Compartment Tests in the ThAI-Facility

2006 ◽  
Author(s):  
G. Weber ◽  
H.-J. Allelein ◽  
F. Funke ◽  
T. Kanzleiter
Keyword(s):  
Relative Humidity ◽  
Large Scale ◽  
High Relative Humidity ◽  
Severe Accident ◽  
Experimental Investigations ◽  
Post Test ◽  
Steel Surfaces ◽  
Accident Conditions ◽  
Adsorption Desorption ◽  
Desorption Model

Post test calculations with the accident codes COCOSYS-AIM and ASTEC-IODE were performed on the iodine multi-compartment tests of the German ThAI program (Thermal hydraulics, Aerosols, Iodine). In the tests transport and adsorption/desorption behavior of gaseous I2 were measured in the 60 m3 vessel with a five-compartment configuration under severe accident conditions. The thermal hydraulic modules in COCOSYS and in the containment part of ASTEC (CPA) are nearly identical but not the iodine modules AIM and IODE. The adsorption/desorption model in AIM is based on ThAI data whereas in IODE correlations derived from laboratory-scale tests are used. A 50-zone nodalisation of the ThAI vessel was used with both codes. COCOSYS-AIM and ASTEC-IODE describe qualitatively correctly the I2 concentration differences of several orders of magnitude in periods with stratified atmosphere and the slow homogenization in a convective mixed atmosphere. However, both codes overestimate the gaseous I2 concentration at high relative humidity. The most likely reason is a slow reaction of deposited I2 to the non-volatile FeI2 on the steel surfaces, which has not been modeled sufficiently yet. Further experimental investigations in the ThAI facility are envisaged. A considering of the ThAI data in the I2 adsorption/desorption correlations may improve future ASTEC-IODE results. Nevertheless, the analyses of the large-scale ThAI iodine tests have been an important validation step for COCOSYS-AIM and ASTEC-IODE demonstrating the capability of multi-compartment I2 treatment.

ASTEC, COCOSYS, and LIRIC Interpretation of the Iodine Behavior in the Large-Scale THAI Test Iod-9

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
G. Weber ◽  
L. Bosland ◽  
F. Funke ◽  
G. Glowa ◽  
T. Kanzleiter
Keyword(s):  
Mass Transfer ◽  
Large Scale ◽  
Saint Paul ◽  
Molecular Iodine ◽  
Severe Accident ◽  
Research Network ◽  
Lumped Parameter ◽  
Post Test ◽  
Iodine Test ◽  
Iodine Transport

The large-scale iodine test Iod-9 of the German Thermal hydraulics, Hydrogen, Aerosols, Iodine (THAI) program was jointly interpreted by means of post-test analyses within the THAI Circle of the Severe Accident Research NETwork (SARNET)/Work Package 16. In this test, molecular iodine (I2) was injected into the vessel dome of the 60 m3 THAI vessel to observe the evolution of its distribution between water, gas, and surfaces. The main processes addressed in Iod-9 are (a) the mass transfer of I2 between the gas and the two sumps, (b) the iodine transport in the main sump when it is stratified and then mixed, and (c) the I2 adsorption onto, and desorption from, the vessel walls in the presence and absence of wall condensation. The codes applied by the THAI Circle partners were the Accident Source Term Evaluation Code (ASTEC)-IODE (IRSN, Saint Paul Lez Durance, France), Containment Code System (COCOSYS)-Advanced Iodine Model (AIM) (GRS, Garching, Germany), and Library of Iodine Reactions in Containment (LIRIC; AECL, Chalk River, ON, Canada). ASTEC-IODE and the Advanced Iodine Model (AIM) are semi-empirical iodine models integrated in the lumped-parameter codes ASTEC and COCOSYS, respectively. With both codes multicompartment iodine calculations can be performed. LIRIC is a mechanistic iodine model for single stand-alone calculations. The simulation results are compared with each other and with the experimental measurements. Special issues that were encountered during this work were studied in more details: I2 diffusion in the sump water, I2 reaction with the steel of the vessel wall in gaseous and aqueous phases, and I2 mass transfer from the gas to the sump. Iodine transport and behavior in THAI test Iod-9 are fairly well simulated by ASTEC-IODE, COCOSYS-AIM, and LIRIC in post-test calculations. The measured iodine behavior is well understood and all measured data are found to be consistent. The very slow iodine transport within the stratified main sump was simulated with COCOSYS only, in a qualitative way. Consequently, this work highlighted the need to improve modeling of (a) the wet iodine adsorption and the washdown from the walls, (b) the I2 mass transfer between gas and sump, and (c) the I2/steel reaction in the gaseous and aqueous phases. In any case, the analysis of the large-scale iodine test Iod-9 has been an important validation step for the codes applied.

scholarly journals Analysis of Computer Modelling Results on Fuel Rods Strength and Condition at Reduced or Absent Cooling Caused by Accident

2021 ◽  
Vol 7 (1) ◽  
pp. 7-16
Author(s):  
Stepan Lys ◽  
Keyword(s):  
Stainless Steel ◽  
Fuel Assembly ◽  
Computer Modelling ◽  
Severe Accident ◽  
Research Centre ◽  
Steel Component ◽  
Spacer Grids ◽  
Fuel Rod ◽  
Standard Problem ◽  
Post Test

The paper describes the phenomenology of fuel rod behaviour in severe accident. As an example, an experiment is described resulting in severe damage of 19 fuel rod assembly of VVER type; it was carried out in the CORA facility in 1993 (Research Centre, Karlsruhe, Germany). Testing conditions and results of post-test investigations of fuel assembly are given. The fuel rod code RAPTA-SFD is briefly dealt with; the code was a participant in the International Standard Problem ISP-36. The basic results are presented acquired by computer modelling CORA-W2 experiment using RAPTA-SFD code. Among the presented experimentally acquired and calculated results, the scope of the data on stainless steel component behaviour is substantial. The tested CORA-W2 fuel assembly contained a significant quantity of steel components, viz., spacer grids, a guide thimble, and a cladding of an absorber element. It is to be borne in mind that the spacer grids and a guide thimble of the updated and upgraded fuel assembly of VVER-1000 are fabricated from Zr-alloy, hence, the relative quantitative characteristics of chemical interactions between materials and stainless steel (Cr-Ni alloy) will be much lower for the up-to-date upgraded fuel assembly under identical conditions.

Simulation of a Containment Spray System Test With the European Lumped-Parameter Codes ASTEC and COCOSYS

2012 ◽  
Author(s):  
Tobias Risken ◽  
Marco K. Koch
Keyword(s):  
Droplet Surface ◽  
Severe Accident ◽  
Test Facility ◽  
High Agreement ◽  
Spray System ◽  
Lumped Parameter ◽  
Post Test ◽  
Temperature And Pressure ◽  
Accident Scenarios ◽  
Increasing Temperature

The presented post-test calculations of the test PACOS Px2.2 performed at Ruhr-Universität Bochum (RUB) regard the predictability of the containment spray system’s effect using the lumped parameter codes ASTEC and COCOSYS. The focus of the calculations is set on the decrease of temperature and pressure in case of severe accident scenarios in light water reactor containments. The comparison of the simulation results to experimental data shows, that pressure and temperature during spraying can be simulated satisfactorily with ASTEC and COCOSYS. While calculating the results of the pressure with high agreement to the experiment, both codes underestimate the temperature more and more with increasing distance along the spray path, as the increasing temperature caused by a moving steam cushion is underestimated. The steam cushion is caused by spray induced convection pushing the warmer atmosphere of the upper test facility compartments into the cooler lower compartments. The temperature increase in the lower zones resulting from the establishing flows cannot be simulated properly, as both codes are not fully capable of calculating the occurring forces between dynamic atmosphere and droplet surface.

Results of the LIVE-L4 Experiment on Melt Behavior in the RPV Lower Head

2010 ◽  
Author(s):  
Alexei Miassoedov ◽  
Thomas Cron ◽  
Jerzy Foit ◽  
Xiaoyang Gaus-Liu ◽  
Alexander Palagin ◽  
...  
Keyword(s):  
Heat Generation ◽  
Molten Pool ◽  
Transient Behavior ◽  
Assessment Process ◽  
Severe Accident ◽  
Mushy Region ◽  
Thermal Hydraulics ◽  
Lower Head ◽  
Post Test ◽  
Crust Thickness

The development of a corium pool in the lower head and its behavior is still a critical issue and is of great importance to assess the severe accident progression consequences to ensure the nuclear plant safety. Therefore, experimental efforts are a vital element of the assessment process, providing hard data and insights of the complicated multi-component, highly turbulent corium pool dynamics. It is essential to consider the whole evolution of the accident, including e.g. formation and growth of the in-core melt pool, characteristics of corium arrival in the lower head, and molten pool behavior after the debris re-melting. These phenomena have a strong impact on a potential termination of a severe accident. The general objective of the LIVE program at the Karlsruhe Institute of Technology (KIT) is to study these phenomena experimentally in large-scale 3D geometry and in supporting separate-effects tests, with emphasis on the transient behavior. The LIVE-L4 experiment was performed using a non-eutectic melt (KNO3-NaNO3) as a simulant fluid. Besides the transient behavior, for which the LIVE-L4 test provides qualified data on temperature evolution in the molten pool and crust growth rates, the experiment addresses other important phenomena, such as the local distribution of heat flux, and the influence of solidification on the thermal-hydraulics of the pool, i.e. the possible existence of a mushy region and its impact on the heat transfer. In the post-test analysis crust thickness profile along the vessel wall, the crust composition and the morphology were determined. The results of this experiment also allow a comparison with findings obtained earlier in other experimental programs. The LIVE-L4 experimental results are being used for the assessment of correlations and development and validation of mechanistic models for the description of molten pool behavior. These calculations are complemented by analyses with the CFD code CONV (thermal hydraulics of heterogeneous, viscous and heat-generating melts) which was developed at IBRAE. The CONV code was applied to simulate the LIVE-L4 test: a) assuming homogeneous heat generation in the liquid and b) accounting for wire heaters used to simulate the heat generation in the melt. Though the results of calculations demonstrate satisfactory agreement with the experimental measurements, deficiencies in the code prediction have been identified regarding e.g. the prediction of the crust thickness. The paper summarizes the objectives of the LIVE program, the main results obtained in the LIVE-L4 experiment and the results of the post-test calculations performed with the CONV code.

Application of Thermal Hydraulic and Severe Accident Code SOCRAT/V3 to Bottom Water Reflood Experiment QUENCH-LOCA-1

2016 ◽  
Vol 2 (2) ◽  
Author(s):  
Alexander Vasiliev ◽  
Juri Stuckert
Keyword(s):  
Nuclear Power ◽  
Hydrogen Generation ◽  
Cooling System ◽  
Reactor Core ◽  
Severe Accident ◽  
Loss Of Coolant Accident ◽  
Post Test ◽  
Core Cooling ◽  
Modeling Code ◽  
Code Quality

This study aims to (1) use the thermal hydraulic and severe fuel damage (SFD) best-estimate computer modeling code SOCRAT/V3 for post-test calculation of QUENCH-LOCA-1 experiment and (2) estimate the SOCRAT code quality of modeling. The new QUENCH-LOCA bundle tests with different cladding materials will simulate a representative scenario for a loss-of-coolant-accident (LOCA) nuclear power plant (NPP) accident sequence in which the overheated (up to 1050°C) reactor core would be reflooded from the bottom by the emergency core cooling system (ECCS). The test QUENCH-LOCA-1 was successfully performed at the KIT, Karlsruhe, Germany, on February 2, 2012, and was the first test for this series after the commissioning test QUENCH-LOCA-0 conducted earlier. The SOCRAT/V3-calculated results describing thermal hydraulic, hydrogen generation, and thermomechanical behavior including rods ballooning and burst are in reasonable agreement with the experimental data. The results demonstrate the SOCRAT code’s ability for realistic calculation of complicated LOCA scenarios.

Analysis of the Quench-14 Bundle Test With M5® Cladding

2009 ◽  
Author(s):  
Jonathan C. Birchley ◽  
Bernd Jaeckel ◽  
Timothy J. Haste ◽  
Martin Steinbrueck ◽  
Juri Stuckert
Keyword(s):  
Severe Accident ◽  
Local Version ◽  
Test Protocol ◽  
Pressurized Water ◽  
Fuel Rod ◽  
Post Test ◽  
The Subject ◽  
Water Reactors ◽  
Accident Conditions ◽  
Cladding Material

The QUENCH experimental programme at Forschungszentrum Karlsruhe (FZK) investigates phenomena associated with reflood of a degrading core under postulated severe accident conditions, but where the geometry is still mainly rod-like and degradation is still at an early phase. The QUENCH test bundle is electrically heated and consists of 21 fuel rod simulators with a total length of approximately 2.5 m. The cladding and grid spacers are identical to those used in Pressurized Water Reactors (PWR) whereas the fuel is represented by ZrO2 pellets. Experiment QUENCH-14 was successfully performed at FZK in July 2008 and is the first in this programme where Zr-Nb alloy M5® is used as the fuel rod simulator cladding. QUENCH-14 was otherwise essentially the same as experiment QUENCH-06, which was the subject of the CSNI ISP-45 exercise. It is also the first of three experiments in the QUENCH-ACM series, recently launched to examine the effect of advanced cladding materials on oxidation and quenching under otherwise similar conditions. Pre- and post-test analyses were performed at PSI using a local version of SCDAP/RELAP5 and MELCOR 1.8.6, using input models which had already been benchmarked against QUENCH-06 data. Preliminary pre-test calculations with both codes and alternative correlations for the oxidation kinetics indicated that the planned test protocol would achieve the desired objective of exhibiting whatever effects might arise from the change in cladding-material in the course of a transient similar to QUENCH-06. Several correlations were implemented in the models, namely Cathcart-Pawel, Urbanic-Heidrick, Leistikow-Schanz and Prater-Courtright for Zircaloy-4 (Zry-4), and additionally a new candidate correlation for M5® based on recent separate-effects tests performed at FZK on M5® cladding samples. Analyses of the QUENCH-14 data demonstrate strengths and limitations of the various models. Some tentative recommendations are made concerning choice of correlation and effect of cladding material.

Förderung der Lesekompetenz mittels reziproken Lehrens: Implementation und Wirksamkeit imRegelunterricht

2016 ◽  
Vol 30 (4) ◽  
pp. 213-225 ◽  
Author(s):  
Helvi Koch ◽  
Nadine Spörer
Keyword(s):  
Good Practice ◽  
Post Test

Zusammenfassung. Ziel war es, die Effektivität zweier Interventionen zur Förderung der Lesekompetenz von Fünftklässlern zu untersuchen. Beide Treatments wurden von Regellehrkräften implementiert. Die eine Intervention war das reziproke Lehren, welches um Selbstregulationsprozeduren angereichert wurde (RT+SRL). Die zweite war eine von Lehrkräften konzipierte lesestrategiebasierte Unterrichtseinheit (Good Practice, GP). Zusätzlich gab es eine No-Treatment-Kontrollgruppe (KG0). Insgesamt nahmen an der Studie N = 244 Schüler teil. Im Rahmen eines Pre-, Post-, Follow-Up-Test-Untersuchungsplans kamen standardisierte Leseverständnisaufgaben, selbstkonstruierte Lesestrategieaufgaben und eine Selbstwirksamkeitsskala zum Einsatz. Kontrastierende Einzelvergleichsanalysen ergaben, dass sich die Schüler der Treatmentbedingung RT+SRL im Vergleich zu den Schülern der Kontrollgruppe zum Post-Test signifikant stärker im Leseverständnis, in der Lesestrategieanwendung und in der Selbstwirksamkeit verbesserten. Gleiches galt für die Lesestrategieanwendung zum Follow-Up-Test. Schüler der Bedingung GP konnten im Vergleich zu KG0-Schülern weder zum Post- noch zum Follow-Up-Test vorteilige Ergebnisse in den drei Kriteriumsmaßen erzielen.

LRS-Elterngruppenprogramm: Teilnehmerzufriedenheit und subjektive Effektivität

2016 ◽  
Vol 5 (1) ◽  
pp. 44-57
Author(s):  
Anke Buschmann ◽  
Bettina Multhauf
Keyword(s):  
Goal Attainment ◽  
Goal Attainment Scaling ◽  
Eine Hohe ◽  
Post Test

Zusammenfassung. Das Ziel vorliegender Studie bestand in einer Überprüfung der Akzeptanz und Teilnehmerzufriedenheit eines Gruppentrainings für Eltern von Kindern mit Lese- und/oder Rechtschreibschwierigkeiten. Zudem sollten erste Indikatoren bezüglich der Wirksamkeit des Programmes untersucht werden. Dazu wurden Daten von 25 Müttern zu 2 Messzeitpunkten (Post-Test, 3-Monats-Follow-up) analysiert. Die Probandinnen nahmen über einen Zeitraum von 3 Monaten an 5 Sitzungen des Programms «Mein Kind mit Lese- und Rechtschreibschwierigkeiten verstehen, stärken und unterstützen: Heidelberger Elterntraining zum Umgang mit LRS» teil. Ein Paper-Pencil-Fragebogen diente zum Post-Test der Erhebung von Teilnahmeparametern, der Zufriedenheit mit dem Training, der Relevanz einzelner Themen und der wahrgenommenen Veränderungen in wichtigen Zielbereichen. Zusätzlich kam eine für das Gruppensetting adaptierte Form des Goal Attainment Scaling zum Einsatz, um das Erreichen persönlich relevanter Ziele unmittelbar nach dem Training sowie 3 Monate später zu erfassen. Die Analyse des Fragebogens zeigte eine hohe Partizipationsbereitschaft der Mütter. Die Rahmenbedingungen des Trainings (Gruppengröße, Dauer des Trainings und der Sitzungen) sowie die didaktischen Methoden wurden als ideal und die Themen als relevant eingeschätzt. Die Mütter sahen sich in der Lage, die Inhalte im Alltag anzuwenden und nahmen positive Veränderungen hinsichtlich Einfühlungsvermögen, Unterstützung des Kindes, Hausaufgabensituation und Beziehung zum Kind wahr. Das Ausmaß des Erreichens individueller Ziele zum Post-Test variierte je nach Zielbereich: Einfühlen und Verstehen (75 %), Optimierung der Hausaufgabensituation (76 %), Unterstützung psychosozialer Entwicklung (86 %), Lese-Rechtschreibförderung (60 %) und war auch 3 Monate später noch vergleichbar hoch. Die Überprüfung der Wirksamkeit hinsichtlich einer Belastungsreduktion und Kompetenzstärkung seitens der Eltern erfolgt aktuell im Vergleich zu einer unbehandelten Kontrollgruppe.

Clinically Meaningful Change

Methodology ◽  
2019 ◽  
Vol 15 (3) ◽  
pp. 97-105
Author(s):  
Rodrigo Ferrer ◽  
Antonio Pardo
Keyword(s):  
Effect Size ◽  
False Negative ◽  
False Negative Rate ◽  
Point Of View ◽  
Skewed Distribution ◽  
Effect Sizes ◽  
False Negatives ◽  
Large Size ◽  
Before And After ◽  
Post Test

Abstract. In a recent paper, Ferrer and Pardo (2014) tested several distribution-based methods designed to assess when test scores obtained before and after an intervention reflect a statistically reliable change. However, we still do not know how these methods perform from the point of view of false negatives. For this purpose, we have simulated change scenarios (different effect sizes in a pre-post-test design) with distributions of different shapes and with different sample sizes. For each simulated scenario, we generated 1,000 samples. In each sample, we recorded the false-negative rate of the five distribution-based methods with the best performance from the point of view of the false positives. Our results have revealed unacceptable rates of false negatives even with effects of very large size, starting from 31.8% in an optimistic scenario (effect size of 2.0 and a normal distribution) to 99.9% in the worst scenario (effect size of 0.2 and a highly skewed distribution). Therefore, our results suggest that the widely used distribution-based methods must be applied with caution in a clinical context, because they need huge effect sizes to detect a true change. However, we made some considerations regarding the effect size and the cut-off points commonly used which allow us to be more precise in our estimates.

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