Modeling Radiological Consequences of Sever Accidents in BWRs: Review of Models Development, Verification and Validation

Transcription

1 Modeling Radiological Consequences of Sever Accidents in BWRs: Review of Models Development, Verification and Validation Mohamed GAHEEN Department of Research on Nuclear Safety and Radiological Emergencies, Egyptian Atomic Energy Authority (EAEA), Egypt Workshop on Advances in Understanding the Progression of Severe Accidents in Boiling Water Reactors July 2017, Vienna, Austria

2 Contents Introduction Atmospheric Transport and Dispersion Models Simulation of Fukushima accidents using ATDMs Hypothetical Fukushima-like accidents Simulation Example of Modeling Radiological Consequences of a Sever Accident Concluding Remarks

3 Introduction The concept of DEFENCE IN DEPTH in design of Nuclear Power Plants consists of FIVE independent LEVELS of protection. FIFTH and final level of defence is to mitigate, through off-site emergency preparedness and response measures, the radiological consequences of potential radioactive releases that may result from an accident. The assessment of radiological consequences include reradioactive releases and nuclide types ( 131 I or 137 Cs,...), dispersion, and concentrations. This requires Pre-defined radioactive source terme, Atmospheric Releases Transport and Dispersion Models (ATDM).

4 Atmospheric Transport and Dispersion Models (1/7) The ATDMs used by WMO (World Meteorological Organization) in simulations of the radionuclide dispersion and deposition from the Fukushima Daiichi nuclear power plant accident, included: MLDP0 (Modèle Lagrangien de Dispersion de Particules d ordre 0 - Canada), HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory Model- US), NAME (Numerical Atmospheric-dispersion Modelling Environment UK), RATM (Regional Atmospheric Transport Model - Japan), and FLEXPART (Lagrangian Particle Dispersion Model - Austria)

5 Atmospheric Transport and Dispersion Models (2/7) The ATDMs are Lagrangian Particle Dispersion Models have the main advantage of tracking particle motion across a non-uniform wind field with varying meteorological conditions. Usually a dispersion model is an off-line model, that is meteorological fields are provided by meteorological model. Examples of the meteorological model outputs are used to drive the ATDMs, are: Weather Research and Forecasting (WRF) Model, MM5 Model, Regional Atmospheric Modelling System (RAMS), and European Centre for Medium-Range Weather Forecasts (ECMWF).

6 Atmospheric Transport and Dispersion Models (3/7) MLDP0 MLDP0 is a Canadian Meteorological Centre (CMC) Lagrangian particle dispersion model of zeroth order designed for long-range dispersion problems occurring at regional and global scales. Dispersion is estimated by calculating the trajectories of a very large number of air particles (also called parcels or fluid elements). MLDP0 is an off-line model that uses meteorological fields of wind, moisture, temperature and geopotential heights, which are normally obtained from the Global Environmental Multiscale (GEM) model.

7 Atmospheric Transport and dispersion models (4/7) HYSPLIT HYSPLIT model of National Oceanic and Atmospheric Administration (NOAA) Air Resources Laboratory s (ARL) is computing simple air parcel trajectories as well as transport, dispersion, chemical transformation, and deposition simulations. HYSPLIT continues to be one of the most extensively used atmospheric transport and dispersion models in the atmospheric sciences community. In addition, the meteorological data already formatted for HYSPLIT that are publicly available from NOAA ARL, the model outputs the can be used to drive HYSPLIT are WRF Model, MM5, RAMS, and ECMWF can be used to drive HYSPLIT.

8 Atmospheric Transport and dispersion models (5/7) NAME NAME is the UK Met Office s Lagrangian particle dispersion model and it is used to model the atmospheric transport and dispersion of a range of gases and particles. It was originally developed to model the transport of radioactive material following the Chernobyl accident. Now, NAME has a wide range of applications including simulating releases of hazardous materials (chemical, biological, radiological and nuclear) and modeling the transport of ash clouds from volcanic eruptions.

9 Atmospheric Transport and dispersion models (6/7) RATM The RATM of Japan Meteorological Agency (JMA) is a Lagrangian tracer transport model, which can be driven by the MESO analysis. The JMA operational products of RATM are the photochemical oxidant information and the volcanic ash fall forecast in Japan. However, RATM was not previously applied to predicting the dispersion and deposition of radionuclides. The preliminary and revised calculations of the JMA-RATM were conducted to provide a meteorological analysis of the Fukushima accident

10 Atmospheric Transport and dispersion models (7/7) FLEXPART The Austrian Meteorological Service (ZAMG) uses FLEXPART, in many of its atmospheric transport modeling applications, ranging from emergency response systems to research purposes, specifically applied to nuclear releases. It can use meteorological fields from the ECMWF numerical weather prediction model or WRF have been developed. ZAMG was involved in a task team of WMO to provide a meteorological analysis of the Fukushima accident, including dispersion and deposition. Participants: NOAA/ARL (lead), ZAMG, JMA, CMC and Met Office, UK

11 Simulation of Fukushima accident using ATDM calculations (1/2) Temporal changes in the air concentrations of 137 Cs at JAEA-Tokai in the simulations using the WMO models for two source terms generally reproduced the observed time trends and the high values observed (13 to 31 March 2011 ) Observed concentration (lines with open circles)

12 Simulation of Fukushima accidents using ATDM calculations (2/2) Distributions of the cumulative 137 Cs surface deposition over eastern Japan on 1 April calculated using WMO models for two source terms.

13 Hypothetical Fukushima-like accidents Simulation (1/2) HYSLPLIT model was adopted to assess the potential impact of 137 Cs released from hypothetical Fukushima-like accidents occurring on potential nuclear power plant sites in Southern China (planned within 10 years) in four seasons. Prior to the calculations, the model was employed to simulate the trans-oceanic transport of 137 Cs from the Fukushima nuclear accident. Observed and modeled 137 Cs concentrations were comparable.

14 Hypothetical Fukushima-like accidents Simulation (1/2) HYSPLIT assessment of impact of 137 Cs released from hypothetical Fukushima-like accident in Southern China in JAN. and JULY.

15 Example of Modeling Radiological Consequences of a Sever Accident (1/9) This work was done as a part of research project: Impact of nuclear accidents on safety of surrounding environment in cooperation with Egyptian Meteorological Authority and Cairo university. The example presents the models that are now available and verfication and vaildation of these models and shows the assessment calculations that have been performed in modling: Radiological consequences of Chernobyl Accident Hypocritical Accident in Egypt Model simulation of Fukushima accident and El Dabaa NPP in Egypt (in progress).

16 Example of Modeling Radiological Consequences of a Sever Accident (2/9) Simulation of Chernobyl Accident For the simulation of the dispersion of the radioactive plume, released by the Chernobyl accident, the FLEXPART model was used. The model is driven by MM5 atmospheric model that can predict meteorological fields with high resolution in time and space. HYSPLIT trajectories of the accident release are also included in the simulation.

17 Example of Modeling Radiological Consequences of a Sever Accident (3/9) Source Term

18 Example of Modeling Radiological Consequences of a Sever Accident (4/9) Distributions of surface air concentrations of 137 Cs using FLEXPART dispersion model are shown The simulation model indicates that the radioactive releases in early hours of 26 April were transported mostly to the north of Chernobyl towards the Scandinavian countries. On April 28th the simulated radioactive cloud crossed the Scandinavia countries and a very strong flow spread the radioactive material in the direction of Iceland and Greenland.

19 Example of Modeling Radiological Consequences of a Sever Accident (5/9) On 1 May the radioactive cloud reached France and initially covered the southern part.. The radioactive cloud covered France on 3 May moved towards the British island and covered it totally during 4 and 5 May. It covered Eastern Europe, Greece and Turkey and also transported northward (the yellow and darkly yellow shaded areas represent concentrations exceeding 10-2 and 1.0 Bq/m 3, respectively).

20 Example of Modeling Radiological Consequences of a Sever Accident (6/9) Model Evaluation The general feature of the transport of the radioactive plume shown was similar to previous calculations. The HYSPLIT air parcel forward trajectories originating from the Chernobyl at the time of the accident agree with initial simulated movement of the radioactive releases towards the Scandinavian countries. The FLEXPART model results of predicted surface air concentration are compared with measurements for the two source terms.

21 Example of Modeling Radiological Consequences of a Sever Accident (7/9) Comparison with measurements and predictions at Mrsa Matrouh and Cairo (estimation of environmental concentrations where no measurements)

22 Example of Modeling Radiological Consequences of a Sever Accident (8/9) HYSPLIT air parcel trajectories agree with the simulated radioactive plume movement

23 Example of Modeling Radiological Consequences of a Sever Accident (9/9) Hypothetical Accident Over Egypt A hypothetical accident of Nuclear Power Plant in El Dabaa, Northwestern coast region of Egypt was simulated on months January and July. The source term for the hypothetical accidental release of 137 Cs is the first three days of Chernobyl source term. DAYS Release rate (Bq/day) Effective initial plume height (m) 13 th E th E th E th E

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27 HYSPLIT air parcel trajectories agree with the simulated radioactive plume movement

28 Concluding Remarks The results depend on the source term and meteorological conditions (seasons). How large and consequence of the radioactive releases of the previous accidents can be described and compared to limit/reduce possible releases in the design of new nuclear power reactors during the accident conditions. The atmospheric dispersion prediction models are useful tool before any releases have occurred or before the plume has reached a specific location, and allow estimations of environmental concentrations where measurements cannot be made.

29 Concluding Remarks contd. It can be concluded that the simulation models comply with the requirements response in nuclear emergences and allow tracking the atmospheric release.

30 Thank you for your attention

31 Reference 1

32 Reference 2

33 Reference 3

34 Second Source Term reference: M. Bocqueta, Parameter-field estimation for atmospheric dispersion: application to the Chernobyl accident using 4D-Var, Q. J. R. Meteorol. Soc. 138: , April 2012.