CFD Application to Hydrogen Risk Analysis and PAR Qualification (original) (raw)
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CFD evaluation of hydrogen risk mitigation measures in a VVER-440/213 containment
Nuclear Engineering and Design, 2010
In the PHARE project "Hydrogen Management for the VVER440/213" (HU2002/000-632-04-01), CFD (Computational Fluid Dynamics) calculations using GASFLOW, FLUENT and CFX were performed for the Paks NPP (Nuclear Power Plant), modelling a defined severe accident scenario which involves the release of hydrogen. The purpose of this work is to demonstrate that CFD codes can be used to model gas movement inside a containment during a severe accident. With growing experience in performing such analyses, the results encourage the use of CFD in assessing the risk of losing containment integrity as a result of hydrogen deflagrations. As an effective mitigation measure in such a situation, the implementation of catalytic recombiners is planned in the Paks NPP. In order to support these plans both unmitigated and recombinermitigated simulations were performed. These are described and selected results are compared. The codes CFX and FLUENT needed refinement to their models of wall and bulk steam condensation in order to be able to fully simulate the severe accident under consideration. Several CFD codes were used in parallel to model the same accident scenario in order to reduce uncertainties in the results. Previously it was considered impractical to use CFD codes to simulate a full containment subject to a severe accident extending over many hours. This was because of the expected prohibitive computing times and missing physical capabilities of the codes. This work demonstrates that, because of developments in the capabilities of CFD codes and improvements in computer power, these calculations have now become feasible.
CFD-based risk assessment for hydrogen applications
Process Safety Progress, 2008
Computational fluid dynamics calculations for gas explosion safety have been widely used for doing risk assessments within the oil and gas industry for more than a decade. On the basis of predicted consequences of a range of potential accident scenarios a risk level is predicted. The development of applications using hydrogen as a clean energy carrier has accelerated in recent years, and hydrogen may be used widely in the future. Because of the very high reactivity of hydrogen, safe handling is critical. For most applications it is not realistic to perform an extensive risk assessment similar to what is done for large petrochemical installations. On the other hand, simplified methods, like venting guidelines, may have a questionable validity for hydrogen. The use of simple methods, if these actually are conservative, will in general predict too high consequences for the majority of scenarios, as these are not able to represent actual geometry and physics of the explosion. In this article a three-step approach is proposed. The initial approach will be to carry out a ''worstcase'' calculation evaluating the consequences if a full stoichiometric gas cloud is ignited. Mitigation measures can also be considered. As a second step, if potential consequences of the initial approach are not acceptable, the assumptions are refined and more calculations are performed to make the evaluations more realistic and reduce unnecessary conservatism of the chosen worst-case scenarios. Typically a number of dispersion calculations will be performed to generate likely gas clouds, which are subsequently ignited. If estimated consequences are still not acceptable, a more comprehensive study, including ventilation, dispersion, and explosion, is performed to evaluate the probability for unacceptable events.
Hydrogen
During an accident, hydrogen distribution in a containment building of a nuclear power plant (NPP) and characteristics of hydrogen depletion by passive autocatalytic recombiners (PARs) differ depending on the thermal-hydraulic behaviors occurring in the containment. A spray system installed in the NPP containment to control the pressure in accident conditions may interact with PAR operations. This study intended to experimentally evaluate the hydrogen removal characteristics of a grid-type PAR when a spray was operating. For the experimental simulation of hydrogen recombination characteristics of the PAR affected by a spray operation, we used the SPARC experimental facility, which was equipped with a pressure vessel capable of controlling the wall temperature with a volume of 82 m3. To measure gas species concentrations, 14 probes each for hydrogen, oxygen, and water vapor were installed. Two tests were designed depending on the spray initiation time. The SSP3 test was an experiment...
Modelling of a Passive Catalytic Recombiner for Hydrogen Mitigation by CFD Methods
2013
Four turbulence models (k-, k-, intermittency, RSM) have been applied in CFD simulations of: gas flow, heat and mass transport, and chemical surface reactions occurring in a passive catalytic recombiner used to remove hydrogen from safety containments of light water nuclear reactors. It was found that differences in model predictions increase with increasing gas flow rate, while at low gas flow rates simulation results converge to those obtained for a limiting case of laminar flow. Heat and mass transfer taking place in the gas phase were identified as essentially two dimensional processes unlike heat exchange with the environment. Large Eddy Simulation technique was used to select the turbulence model giving the best prediction of the hydrogen recombination rate.
Nuclear Engineering and Design, 2020
In this study, an accurate and efficient method is proposed to simulate hydrogen mitigation using catalytic recombiner in a nuclear reactor containment. Using a point model and a detailed set of reaction kinetics equations, the variation of hydrogen reaction rates with surface temperature for various hydrogen and water vapor concentration are found. The entire reactant domain is divided into two zones, Zone 1 and Zone 2. In Zone 1, when the mixture is heated, there is a sudden onset of surface reactions at a threshold temperature (catalytic auto ignition temperature) beyond which the reaction rate falls. In Zone 2, the reaction rate gradually builds up beyond a threshold temperature, reaching maxima (maximum reaction temperature) and then falls. Correlations for catalytic ignition/maximum reaction rate temperature and reaction rates have been developed for both the zones. Using the developed correlations, a recombiner CFD model is evolved to simulate the REKO-3 experiments performed in REKO test facility to validate the recombiner model. The present investigation reveal the importance of radiation heat transfer in correctly predicting the catalyst plate temperature. From numerical computations, the best suited radiation model is identified. A parametric study is then carried out to predict the highest catalyst plate temperature under diverse operating conditions. From the obtained results, an engineering correlation is developed which successfully predicts the highest plate temperature for the entire range of REKO-3 data.
CFD Modeling of Hydrogen Releases and Dispersion in Hydrogen Energy Station
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Gap Analysis of CFD Modelling of Accidental Hydrogen Release and Combustion
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Hydrogen is expected to play an important role in the energy mix of a future lowcarbonsociety, as it is stated in the European Strategic Energy Technology Plan ofthe European Commission (COM 2007 - 723) and in the Hydrogen, Fuel Cells &Infrastructure Technologies Program-Multi-Year Research, Development, andDemonstration Plan of the USA Department of Energy (DoE 2007).Hydrogen safety issues have to be addressed in order to demonstrate that the widespread deployment and use of hydrogen and fuel cell technologies can occur withthe same or lower level of hazards and associated risk compared to theconventional fossil fuel technologies. Computational Fluid Dynamics (CFD) isconsidered one of the tools to investigate safety issues related to the production,storage, delivery and use of hydrogen. CFD techniques can provide a wealthyamount of information on the dynamics of hypothetical hydrogen accident and itsconsequences. The CFD-based consequence analysis is then used in riskassessments. I...
Improvements in a CFD code for analysis of hydrogen behaviour within containments
Nuclear Engineering and Design, 2007
The use of CFD codes for the analysis of the hydrogen behaviour within NPP containments during severe accidents has been increasing during last years. In this paper, the adaptation of a commercial multi-purpose code to this kind of problem is explained, i.e. by the implementation of models for several transport and physical phenomena like: steam condensation onto walls in presence of non-condensable gases, heat conduction, fog and rain formation, material properties and criteria for assessing the hydrogen combustion regime expected. The code has been validated against several experiments in order to verify its capacity to simulate the following phenomena: plumes, mixing, stratification and condensation. Moreover, two tests in an integral large enough experimental facility have been simulated, showing that the well-mixed and stratified conditions of the test were reproduced by the code. Finally, an example of a plant application demonstrates the ability of the code in this kind of problems.
Simulation of hydrogen mitigation in catalytic recombiner. Part-II: Formulation of a CFD model
Nuclear Engineering and Design, 2011
This paper aims at accurate modelling of a Passive Catalytic Recombiner used for hydrogen mitigation in the nuclear power plant containments. In order to assess the performance of the recombiner through numerical simulations, it is required to accurately predict the catalytic reactions. There are various detailed reaction mechanisms available in the literature for prediction of hydrogen-oxygen reaction over a platinum surface. While a single step reaction rate expression is always sought in order to obtain numerical predictions economically, a detailed reaction mechanism that includes several elementary reactions and intermediate species is likely to produce more accurate predictions. The paper compares the solution from two of competing models, one a single step reaction and the other a multiple reaction model. A new single step rate expression is also derived from the detailed mechanism after simplifying it for the present problem. The paper also considers the diffusion controlled model that assumes rapid reaction rates for which the surface chemistry is not required at all. In order to find the best suited approach to model the surface chemistry, CFD simulations were performed with FLUENT code using available experimental data from the literature. The current study reports comparison up to 4% H 2 mole fraction in dry air with catalyst temperature varying from 300 K to 800 K. It is demonstrated that the new single step model is able to satisfactorily predict the data as well as the detailed chemistry model. The diffusion controlled model is shown to over-predict the data.
Nuclear Engineering and Design, 2008
The French Atomic Energy Commission (CEA) and the Radiation protection and Nuclear Safety Institute (IRSN) are developing a hydrogen risk analysis code (safety code) which incorporates both lumped parameter (LP) and computational fluid dynamics (CFD) formulations. In this paper we present the governing equations, numerical strategy and schemes used for the CFD approach. Typical numerical studies will be presented for hydrogen distribution and combustion applications in realistic large geometries.