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DEVELOPMENT OF A COMPREHENSIVE DECISION SUPPORT SYSTEM FOR NUCLEAR EMERGENCIES IN EUROPE FOLLOWING AN ACCIDENTAL RELEASE TO ATMOSPHERE

Objective

Task description

The purpose of the research is to develop the essential ingredients of a decision supporting system which has the potential for wide scale application in Europe.

The structure of the system will be modular in form with separate components corresponding to data input facilities, data banks, atmospheric transport, environmental and economic models, logic routines, output facilities, etc.

The modular structure of the system and the detailed parameterization of calculational procedures will provide great operational flexibility which will enable the system to cope with differing:
amounts and quality of measured and radiological data;
site and source term characteristics;
national regulations, emergency plans, responsibility structures;
needs of the user.

In addition to its role in providing decision support in the case of a real emergency, the structure and design of the system will be such that it can be used as a powerful tool in training of decision makers, in exercising emergency plans and as a means for gaining experience with emergency plans and recommendations for long term countermeasures and recovery actions.

The activities in the first project period 1990 to 1991 will be concentrated on the following areas:

Project 1 (KfK)
Development of a real time system for aiding decisions about emergency actions in the early phase of an accident, such as evacuation and sheltering. Besides the estimation of radiological quantities, the modelling of emergency actions, and the evaluation and ranking of alternative actions by an expert system, emphasis is given to the installation of an operational system as framework for a comprehensive decision support system.

Project 2 (GSF)
In the framework of a preceding research programme a real time emergency dose prediction system including countermeasures has been developed. This computer code has been designed for adaption to the different living habits, climatic and agricultural conditions in the different regions of the European Community.
It is intended to continue this work with the aim to integrate the existing code into the framework of the decision support system under development.

Project 3 (CEA and NCSR Demokritos)
A code system calculating the atmospheric dispersion of pollutants will be developed, based on the MC31 code which solves the diffusion-advection equation by Monte-Carlo techniques, and the ADREA code, which is a 3-dimensional time-dependent transport code, suitable for complex terrain.

Project 4 (ENEA)
The phase of the evaluation of input parameters for meteodiffusive codes plays a very important role during a run of an emergency system, so it is essential to develop a software package to provide in real time those input parameters which are neither directly measured nor available on the database, and to format the data as required by the specific input files of the models. In particular, this package should include several routines to estimate input model parameters like atmospheric stability category; mixing layer depth; scaling parameters (friction velocity, Monin-Obukhov length, etc.).

In the present research project, the feasibility of using stochastic methods (grey box models) for the local prediction of some of the above mentioned parameters will be studied.

Project 5 (Risoe):
A portable atmospheric dispersion module will be created, based on the combination of our mesoscale puff model RIMPUFF and an updated version of the diagnostic, nonhydrostatic flow model LINCOM.
A functional demo-system will be established.

Project 6 (ICSTM)
Under the postChernobyl programme a computer model, 3-DRAW, has been developed in a preliminary form as a tool to simulate atmospheric dispersal and deposition out to continental scale distances, in the context of real time assessment (following a nuclear accident). This project will concentrate on validation and improvement by addressing:
the performance and accuracy of the model in critical meteorological situations such as frontal systems;
improved parameterization, particularly with respect to conditions in the boundary layer, and their assessment from available meteorological data (collaboration with ENEA here);
the practical use of the model in an emergency situation including its combined use with measurements to optimize and update predictions;
investigation of potential benefits of advances in computer technology, specifically through parallel processing techniques.

Project 7 (SMHI)
An extension of a 3-dimensional Eulerian mesoscale dispersion model to the European scale will be performed, for the use as an operational real time model.
The real time emergency dose prediction system, EURALERT, is being used as a basis for the food chain transport module, the dose module and for parts of the countermeasure modules in a proposed decision support system. According to the requirements of this system, a refined version, EURALERT-91, of the computer code has been designed and is under development. The main features of EURALERT-91 are as follows.
EURALERT-91 consists of a frame program and a number of modules.
During the development of EURALERT-91, the frame program has to do the tasks which will be performed later on by the operation system, OSY, especially input and output operations and controlling the sequence of the modules. In the established decision support system, the frame program is no longer necessary.
The modules of EURALERT-91 are outlined to fit into the decision support system without changes or, at most, minor adaptions. For this purpose, all input and output operations have been banished from the modules and they are coded as subroutines without parameter list.
Input and output data are submitted to and from the modules via COMMON blocks located in include files together with the definition of these data. Progress in the capabilities of workstations regarding available random access memory (RAM), make it possible, at least for the greater part of the interfaces, to avoid data transfer from one module to another via external files but to keep the data inside the memory. This implies, however, an effective use of data space and limitations on the dimensions of the calculated data.
For the purpose of an easy adaptability, the declaration of dimensions is performed by PARAMETER statements and submitted to the modules via include files.
According to these features, the computer code EURALERT has been disintegrated and modified and is being recomplied as EURALERT-91.

A complete set of calculation tools has been drawn, expanded and improved in the form of a system code permitting forecasting or real time dispersion computations to be used in dose assessments in case of radioactive release in air. The developed code system is based on the MC 31 and ADREA codes, including descriptive data homogenization. The interface and data homogenization work will cover topics such as ADREA and MC 31 interface introducing a common 3-dimensional representation of the orography of sites. A common support programme development to perform automatic and optimum discretization of the complex domain under consideration has been developed.

A software package for the assessment of meteorological parameters needed by real time atmospheric dispersion models has been developed. The general structure and characteristics of the meteorological preprocessor have been defined. The preprocessor is independent of the atmospheric dispersion model(s) included in the comprehensive decision support system and is flexible with respect to the meteorological data that can be available on site (ranging from a single wind measurement and cloud cover observation to vertical profiles of wind and temperature). All functions of the module (preparation of input data, selection of the parameterization method, analysis of the results) are driven by a user friendly menu. The apckage has been implemented on a RISC workstation in OSF MOTIF environment

The meterological preprocessor estimates boundary layer parameters generally used by atmospheric dispersion models such as mixing height, friction velocity, Monin-Obukhov length etc. In order to identify the most suitable and updated methods for deriving these parameters, a review of recent works available in the literature was carried out. An agreement on the structure of the preprocessor has been reached and technical information and suggestions regarding the methods for estimating the meteoroloical parameters exchanged with Risoe National Laboratory.

New and updated models for plume rise, building wake and penetration of the inversion lid are being introduced in RIMPUFF along with a better model for calculating the gamma doses from puffs. A system for coupling RIMPUFF with the flow model LINCOM has been implemented on a personal computer. LINCOM is under improvement by introducing temperature forcing so that it is able to deal with both unstable and stable situations. In addition to the neutral, a method for calculating a mass consistent flow field based on data from a combination of the Flow Fields from several wind stations will soon be operational. Work has started on the modelling of chemical reactions involving the materials released to the atmosphere and will be included in RIMPUFF. In cooperative work, the mesoscale puff (RIMPUFF) is being coupled to the regional scale dispersion model, RAM, and methods for connecting the HIRLAM flow model to RIMPUFF are being investigated in order to establish an integrated sytem for calculating the dispersion of toxic material over long. (1000 km) and medium range (100 km).

A simple reprocessing system for use with RIMPUFF has already been established in connection with the development of a model for the dispersion of virus released to the atmosphere.

RIMPUFF and LINCOM are being evaluated using data from 2 complex terrain experiments. In an orographically influenced dispersion scenario, potential has been found for improvements by the use of the high resolution mean flow model, LINCOM.

Initial development has been undertaken of a model to simulate atmospheric dispersion of an accidental release out to continental scale for use in the event of a nuclear accident. In conjunction with data from a weather forecasting model, this is designed to provide predictons of the levels of contamination in air and deposited on the ground. A Monte Carlo approach has been chosen, representing a release as an assembly of particles advected according to the mean 3-dimensional wind fields but with random displacements to represent smaller scale eddies and turbulence. Each particle represents variable amounts of selected nuclides, these quantities being depleted during transport according to the probability of decay or deposition. Deposition is calculated due to both dry and wet processes, the latter with provision to distinguish between convective and frontal precipitation where meteorological data from forecasting models enables this (the height of origin of material scavenged can be very different in the 2 cases).

The model calculates time integrated atmospheric concentrations in ground level grid cells over specified periods of time (eg 3 or 6 hourly intervals) and cumulative dry and wet deposition over the same grid, spanning the map area. It reflects a novel feature of the model in that contributions to exposure are calculated along the whole trajectory of each particle rather than just using positions at certain times (thus reducing the number of particles which it is necessary to track and reproducing the observed quantities more closely). This statistical approach can also be interpreted to give a more probabilistic indication of exposure at a location of interest.

The model has been constructed in such a way that it can be readily adapted ot meteorological data form different national or European forecasting models. An initial version of the code is operational.

The MC31 and ANDREA-1 codes have been merged, the former performing pollutant dispersion calculations in the wind field produced by the latter. The topography of the complex terrain they both take into account is simulated by the DELTA code. The current version of the DELTA code may accept user supplied data or may directly use digitized charts built according to French or Greek specifications. The modellization of the topography in the DELTA code is obtained using adjacent traingular surfaces in number and size depending on the accuracy required. Each triangle simulating the ground surface may have its own characteristics. Each user defined cartesian calculation cell can include many ground surface elements and corresponding one eighth type surface and volume porosities, which are important items in hydrodynamic calculations, are analytically computed. For subsequent air and ground energy exchange calculations, the DELTA code determines each triangular surface element to be either sunny or shaded, given the geographical location of the area under treatment and the timing of the event studied.

A review study has been carried out concerning the mathematical modelling, in Eulerian formulation, of clouds, precipitation and wet deposition. Based on the review, a single prognostic equation for the whole of water substance will be utilized for the present model. This has the advantage of model simplicity and the potential for lower computer time by avoiding the addition of more differential equations for solution. In addition no explicit modelling is required for microphysical proceses which are difficult to verify directly. The energy transport is expressed in terms of internal energy instead of liquid potential temperature.

A dispersion model, based on an Eulerian mesogamma scale model, has been adapted to the European scale. The model descriptions of the emission phase of an accidental release and of the initial 24 hour plume dispersion have been developed. The model code has been recorded to give a more general structure and emphasis has been put on increasing the portability of the code. The system was recorded to be independent of projection, although the map projections used have to be specified, and it is therefore feasible to use analyzed or forecast meteorological input fields from various databases. The interface to such data, however, has to be carefully specified.

The system has been used with either HIRLAM or ECMWF meterological input data in some different test calculations. HIRLAM data have only been applied to non real time simulations while ECMWF data have also been used for forecasts in real time applications. A model application, focusing on the importance of accurate precipitation information, has been performed using some data from the Chernobyl case. A comparison between the model calculated (using wind fields for HIRLAM) and deposition of caesium-137 shows very good agreement. The agreement depends to a large extent on the accuracy in space and time of the precipitation fields used in the model. The importance of precipitation for the deposition pattern can be seen from a comparison of the detailed analysis of precipitation amounts with observed caesium-137 deposition therefore the uncertainty of precipitation analyses and forecasts has to be addressed.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Forschungszentrum Karlsruhe Technik und Umwelt GmbH
Address

76021 Karlsruhe
Germany

Participants (7)

Commissariat à l'Energie Atomique (CEA)
France
Address
Centre D'études De Fontenay-aux-roses
92265 Fontenay-aux-roses
Ente per le Nuove Tecnologie, l'Energia e l'Ambiente (ENEA)
Italy
Address
Via Vitaliano Brancati 48
00144 Roma
GSF - FORSCHUNGSZENTRUM FUER UMWELT UND GESUNDHEIT GMBH
Germany
Address
Ingolstaedter Landstrasse 1
85764 Neuherberg
Greek Atomic Energy Commission
Greece
Address
Attikis
15310 Athens
IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE
United Kingdom
Address
South Kensington Campus
London
RISOE NATIONAL LABORATORY
Denmark
Address
Frederiksborgvej 399
Roskilde
Swedish Meteorological and Hydrological Institute
Sweden
Address
1,Folkborgsvoegen
601 76 Norrköping