1、1MULTIDIMENSIONAL SIMULATION OF HYDROGEN DISTRIBUTION AND COMBUSTION IN SEVERE ACCIDENTSCO-ORDINATORW. ScholtyssekForschungszentrum KarlsruhePostfach 364076021 KarlsruheGermanyTel.: + 49 7247 82 5525Fax: + 49 7247 82 5508E-mail: werner.scholtyssekpsf.fzk.deLIST OF PARTNERS1. Forschungszentrum Karlsr
2、uhe, Institut fr Kern- und EnergietechnikU. Bielert, W. Breitung, S. Dorofeev, A. Kotchourko, R. Redlinger2. Institut de Radioprotection et de Surete Nucleaire, IRSNJ-P. LHeriteau, P. Pailhories, M. Petit3. Framatome ANP GmbHJ. Eyink, M. Movahed, K-G. Petzold4. GRS M. Heitsch5. Kurchatov Institute V
3、. Alekseev, A. Denkevits, M. Kuznetsov, A. Efimenko, M.V. Okun6. JRC Ispra, JRC PettenT. Huld, D. BaraldiCONTRACT N: FIKS-CT1999-0004EC Contribution: EUR 700.000Partners Contribution: EUR 720.487 Starting Date: February 2000 Duration: 36 monthsVersion 18. 8. 20032CONTENTSLIST OF ABBREVIATIONS AND SY
4、MBOLSEXECUTIVE SUMMARYA. OBJECTIVES AND SCOPEB. WORK PROGRAMMEB.1 Pre-Test Analysis and Test Definition B.2 Tests on Flame Propagation in Room Chains at Small ScaleB.3 Large Scale Tests on Flame Propagation in Multicompartment GeometryB.4 Analysis, Model and Code Validation, and Plant AnalysisC. WOR
5、K PERFORMED AND RESULTSC.1 ExperimentsC.1.1. Medium Scale TestsC.1.2 Large Scale TestsC.1.3 Verification of the -criterion for Multi Compartment GeometryC.2 Code DescriptionC.3 Blind Pre-Test CalculationsC.4 Analysis of Combustion TestsC.4.1 Code Comparison of Medium Scale TestsC.4.2 Code Comparison
6、 of Large Scale TestsC.5 Full Scale Application C.5.1 Maximum Admissible Mesh Size for CFD CaluclationsC.5.2 Application of Combustion Regime CriteriaC.5.3 Full Scale Benchmark CONCLUSIONREFERENCESTABLESFIGURES3LIST OF ABBREVIATIONS AND SYMBOLSBR Blocking RatioCFD Computational Fluid DynamicsCPU Cen
7、tral Processing UnitDDT Deflagration to Detonation TransitionDLF Dynamic Load Factor EBU Eddy Break UpED Eddy DissipationFA Flame AccelerationFCFS Fully Compressible Flow SolverFZK Forschungszentrum KarlsruheIKET Institut fuer Kern- und Energietechnik (FZK)IRSN Institut de Radioprotection et de Sure
8、te NucleaireJRC Joint Research CentreKI Kurchatov InstituteLMNFS Low Mach Number Flow SolverNPP Nuclear Power PlantPWR Pressurised Water ReactorRUT Large Scale Combustion Facility, KI, MoscowSG Steam Generator4EXECUTIVE SUMMARYThe HYCOM project, an EC Cost Shared Action, was carried out with contrib
9、utions from six organisations, which included research and expert organisations as well as industry. The project aimed at extension of the experimental data base which is needed for the verification of newly developed analysis methods and codes to predict hydrogen combustion behaviour and correspond
10、ing loads on representative scale. An experimental programme in medium and large scale facilities has been performed with combustion modes, ranging from slow to fast turbulent deflagration, that were not yet covered by previous experiments. The main focus was on complex, multi-compartment geometry a
11、nd on inhomogeneous hydrogen concentrations in dry test atmospheres and at ambient temperatures, which allowed precise definition of the initial and boundary conditions. Detailed data were obtained revealing specific effects of scale, multi-compartent geometry and venting. It was observed that the f
12、low geometry has some influence on critical conditions for fast combustion regimes, however applicability of the -criterium was confirmed also for complex enclosures. The data base has been used for the validation of criteria, models and codes which were developed by the partners. For several tests,
13、 blind predictive calculations were performed. Lumped parameter codes performed reasonably well in cases with slow flames, CFD codes showed better performance for fast combustion. Some phenomena like flame quenching or oscillation are not yet modelled, also description of heat losses needs improveme
14、nt. Post-test calculations were performed for selected tests, which gave valuable information on code capabilities and on the range of validity of models and code control parameters. A number of suitable tests were identified for benchmarking purposes and relevant data are made available to interest
15、ed users outside the project. After the validation stage, a scaling-up exercise was performed in order to evaluate the applicability of the codes to real-scale plants. The exercise was carried out on a simplified PWR containment. The assessment of the results of the validation phase and of the chall
16、enging containment calculation exercise allows a deep insight in the quality and capabilities of the CFD tools which are currently in use at various laboratories. The HYCOM project contributed significantly to the establishment of a meaningful method to assess hydrogen risk in a nuclear plant contai
17、nment. It consists of three steps: Calculation of the time dependent gas- and temperature distribution using CFD codes Assessment of the potential combustion mode using state-of-the-art combustion criteria If combustion criteria are met, the impact of the combustion needs to be calculated. The codes
18、 under investigation in this project are suited to predict the overall course of combustion events and of the containment impact within their validation range. This project demonstrates that the quality of validation work is of prime importance. In addition to validation runs, reasonable physical mo
19、dels for input parameters, depending on basic mixture properties, should be validated. This could help to further reduce conservatism and uncertainties of plant application calculations.5A. OBJECTIVES AND SCOPEDuring a severe accident in a nuclear power plant, large quantities of hydrogen and steam
20、can be produced which may threaten containment integrity. As a consequence, early containment failure due to hydrogen combustion was identified as a major contributor to large land contamination in various probabilistic risk studies. In recent years a general consensus has been reached among Europea
21、n safety authorities, vendors, utilities and research organisations, that early containment failure must be excluded on a deterministic basis, and that significant accident consequences must be limited to the plant site. To prove that the new safety goal will be met, numerical methods are under deve
22、lopment. They must be validated on realistic scale and under prototypical conditions to allow reliable prediction of hydrogen distribution, combustion processes and control system behaviour in large complex containment geometries with acceptable uncertainties and little conservatism. Therefore the d
23、evelopment of reliable physical models and adequate numerical methods is a necessary basis for integrated analysis of severe accidents, thereby enhancing safety and avoiding unnecessary conservatism. To ensure this, the analytical tools must be validated on an experimental data base which covers rel
24、evant aspects of the hydrogen problem.Hydrogen combustion can occur in various modes depending on composition, scale and geometry. Consequently, different loads can be expected. Global pressure loads affect the containment building itself. In most cases, the level of loads depends on the total amoun
25、t of hydrogen burnt, initial conditions (pressure and temperature), and an average rate of the combustion process. The local loads are more sensitive to details of hydrogen distribution inside containment, to geometry, venting areas and connecting areas between subcompartments. It is possible that t
26、he global pressure rise is below some certain safety level for a containment, but local loads are capable to damage seriously specific containment components, internal walls and safety equipment. Existing analysis methods and codes are mainly based on experimental data from single-compartment geomet
27、ry and with uniform initial gas distributions. Earlier experimental programmes on multicompartment hydrogen combustion were usually limited due to safety requirements of test facilities. Tests in the facility that was used in this project were free of such safety constraints. The main objectives of
28、previous tests in this facility were, however, to study necessary conditions for DDT. Complementary large scale hydrogen deflagration tests are therefore necessary for improvement of the knowledge base in the hydrogen field. The HYCOM project included the following main objectives:a) Studies of prem
29、ixed hydrogen flames in non-uniform mixtures and multi-compartment geometry under conditions and scale representative for severe accidents. b) Evaluation of effects of scale and mixture properties on hydrogen combustion behaviour. c) Test and refinement of criteria for effective flame acceleration (
30、-criterion). d) Extension of the experimental data base on hydrogen combustion that is necessary to benchmark containment analysis methods, criteria, and codes. e) Validation of models and codes on experimental data and identification of ranges of applicability of modelling approaches, e.g. lumped p
31、arameter and CFD techniques.f) Demonstration of code capabilities by full scale plant analysis.The following steps were taken to respond to the objectives:A) An extensive experimental programme was carried out by one of the partners (KI), on two different scales, with the focus on combustion regimes
32、 which ranged from slow to fast 6turbulent deflagrations. The main interest was in geometrical aspects and hydrogen concentration gradients. Although steam would generally be present in accident atmospheres, dry atmospheres at ambient temperatures were used in the tests. This was justified since the
33、 effect of steam on the reactivity of hydrogen-air mixtures was studied extensively and is considered to be sufficiently well known 1, 2. In addition, tests at ambient temperatures allow a more precise definition of the initial and boundary conditions.The programme yielded a great number of test res
34、ults which provides a valuable data base for model development and code validation. The experimental part was prepared and accompanied by pre-test analyses. B) Validation of the codes was performed against small and large-scale experiments. The work focused on calibrating the combustion models again
35、st experimental data of flame speed and pressure. The results of test analysis activities were assessed and compared. C) Finally, the simulation of hydrogen combustion in full size containment was performed. This exercise intended to demonstrate that the current codes and computer resources are capa
36、ble of describing deflagration phenomena in a nuclear containment. Real size plant calculations were not feasible until very recently, and it is one of the first times that such an exercise has been carried out. Another aim was to assess the effect of scaling-up from small and large-scale simulation
37、s to real plant computation on the predictive capabilities of the codes. B. WORK PROGRAMMEB.1 Pre-test analysis, test definitionPre-test calculational work was carried out for the planning of small and large scale experiments as performed in B2. and B3. Available numerical tools were used for the de
38、finition of the boundary and initial conditions, the definition of instrumentation type, number and location, and the prediction of expected conditions during tests, e.g. combustion regimes and loads, and prediction of performance of components and instrumentation.An important way to prove the predi
39、ctive capabilities of severe accident codes is to perform blind pre-test calculations. Such an exercise was agreed as part of the HYCOM project. The blind pre-test calculations were especially made for large scale experiments in the RUT facility. Two experiments were selected, which were performed i
40、n 2000 in RUT configuration 1. Simulation results were requested to be submitted to a central server before a given deadline. In a second round, the exercise was repeated to see wether the predictive quality of the codes could be further improved. Four tests in the RUT facility were selected, howeve
41、r in a modified geometry (configuration 2), which was investigated in the second experimental campaign in 2001. The data to be delivered by the partners were pressure evolution and flame arrival times for selected locations corresponding to the measurement locations in the tests. In total, seven cod
42、es were involved in the blind pre-test calculations, and 23 calculations were delivered. B.2 Tests on flame propagation in room chains at small scale Tests at relatively small scale addressed characteristic features of turbulent flame propagation. Special attention was given to separate effects incl
43、uding ignition location, venting, heat losses, concentration gradients, blockage ratio changes, channel cross-section changes and multiple connections on the characteristic features of hydrogen flame propagation 7The tests were performed in a research facility using combinations of smaller test unit
44、s, the DRIVER and TORPEDO tubes. These are obstructed channels of about 170 and 525 mm inner diameter respectively. The facility provided the capability to study flame propagation in obstructed channels with different blockage ratios (0 - 0.9), varying crosss sections and initially non-uniform combu
45、stible mixtures. Detailed experimental data were obtained on turbulent flame propagation in obstructed tubes. The measured data revealed specific effects of venting, ignition location, mixture gradients and blockage ratio changes. The data are useful to test turbulent combustion models both qualitat
46、ively and quantitatively.B.3 Large scale tests on flame propagation in multicompartment geometryLarge scale tests in multicompartment geometry were performed in the large, robust RUT facility to examine processes of turbulent flame propagation in room chains, in multi-compartment geometry and in non
47、-uniform mixtures on reactor typical length scales. The geometry included up to 6 compartments with obstructions for effective flame acceleration and an optional venting compartment. Tests were carried out in two different configurations with different hydrogen concentrations and ignition locations.
48、 They addressed processes with flame speeds in slow and fast deflagration regimes. The mixture compositions were chosen to provide conditions close to the critical compositions for flame acceleration. The gas distribution system provided the possibility to arrange different hydrogen concentrations i
49、n two parts of the facility. Local H2-concentrations were measured with a sampling method using eight sampling ports. The mixture was ignited with a weak electric spark. The measurement system included collimated photodiodes as well as piezoelectric and piezoresistive pressure transducers. Also integrating heat-flux meters were used. The measured data include flame arrival times throughout the facility, pressure measurements, and heat loss characteristics, both from heat flux meters and pressure transducers. The latter was achieved by the application of he
