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VERBESSERUNG DER MODELLE ZUR BERECHNUNG DER TROCKENEN ABLAGERUNG VON AN AEROSOLTEILCHEN GEBUNDENEN RADIONUCLIDEN

Objectif

THE DRY DEPOSITION OF RADIONUCLIDES BOUND TO AEROSOL PARTICLES AND OF RADIOIODINE ON VEGETATION AND THE GROUND IS A VERY IMPORTANT FACTOR IN CALCULATING HUMAN EXPOSURE TO RADIATION THROUGH INGESTION AND GROUND RADIATION.
IT IS STANDARD PRACTICE AT PRESENT TO USE A CONSTANT DEPOSITION VELOCITY VD FOR AEROSOLS AND FOR IODINE WHEN CALCULATING THE DOSE; SEE, FOR EXAMPLE, (BU79), (BU83). SINCE THE DEPOSITION VELOCITY DEPENDS ON MANY PARAMETERS (E.G. PARTICLE DIAMETER, PARTICLE DENSITY, WINDSPEED OR SHEARING STRESS SPEED, TURBULENT DIFFUSION COEFFICIENTS, AIR HUMIDITY, TYPE OF GROUND VEGETATION, ETC.), A MORE ACCURATE DETERMINATION OF VD IS OF THE GREATEST IMPORTANCE TO REALISTIC DOSE CALCULATION.
AT THE INSTITUTE FOR RADIATION PROTECTION IN NUCLEAR TECHNOLOGY AT THE RWTH AACHEN, MODELS AND COMPUTER PROGRAMMES WERE DEVELOPED FOR THE THEORETICAL DESCRIPTION OF DRY DEPOSITION WITH DUE REGARD TO THE ABOVE-MENTIONED PARAMETERS UNDER A RESEARCH PROJECT (ST.SCH.729) SUPPORTED BY THE FEDERAL MINISTER OF THE INTERIOR OF THE FEDERAL REPUBLIC OF GERMANY. THE COMPARISON OF THE RESULTS OF THE MODEL CALCULATIONS PERFORMED SO FAR WITH THE EXPERIMENTAL RESULTS PUBLISHED IN THE LITERATURE SHOWED ASTONISHINGLY GOOD AGREEMENT AS REGARDS THE DEPOSITION VELOCITIES.
THE TURBULENT DIFFUSION COEFFICIENT IS A SIGNIFICANT PARAMETER IN MODEL CALCULATIONS FOR DETERMINATION OF THE TRANSPORT OF AEROSOL PARTICLES (OR IODINE) TO THE GROUND AND THE VEGETATION.
IT IS MAINLY IN RESPECT OF DEPOSITION WITHIN THE VEGETATION THAT ONLY A FEW MEASURED VALUES OR ADEQUATELY DETAILED THEORETICAL MODELS ARE AVAILABLE FOR THE TURBULENT DIFFUSION COEFFICIENTS.
FOR THIS REASON, IT IS INTENDED TO DETERMINE THE HEIGHT-DEPENDENT EVOLUTION OF THE TURBULENT DIFFUSION COEFFICIENT IN BOTH FIELD EXPERIMENTS AND THE WIND TUNNEL. THE MEASUREMENTS WILL SIMULTANEOUSLY PROVIDE HEIGHT-DEPENDENT WINDSPEED PROFILES WITHIN AND ABOVE THE VEGETATION.
Measurements of the influence of height on the diffusion coefficients of turbulence have been carried out both in the field and in a wind tunnel. These results have been used to calculate deposition velocity.

Measurements have been made of the vertical distribution of wind velocity and eddy diffusion coefficients in and above different kinds of vegetation (both field and wind tunnel experiments). These results were used for the calculation of the deposition velocity of radionuclides.
IN ORDER TO BE ABLE TO MAKE STATISTICAL STATEMENTS ON THE EVOLUTION OF THE DIFFUSION COEFFICIENT AS A FUNCTION OF THE MEASURED QUANTITIES NORMALLY USED IN DOSE CALCULATIONS (WINDSPEED, WIND DIRECTION, DIFFUSION CATEGORY) AND THE SITE CHARACTERISTICS (GROUND VEGETATION IN THE VICINITY OF THE EMITTING INSTALLATION), IT IS NECESSARY TO DOCUMENT BOTH THE METEOROLOGICAL BOUNDARY CONDITIONS AND THE VEGETATION CONDITIONS STUDIED IN THE CASE OF EACH MEASUREMENT.
THE MEASUREMENTS WITHIN THE VEGETATION ARE CARRIED OUT WITH THREE-DIMENSIONAL MICRO-ANEMOMETERS.
IN ORDER TO SUPPLEMENT THE FIELD MEASUREMENTS, THE FLOW CONDITIONS CLOSE TO THE GROUND WILL, IN PARTICULAR, BE STUDIED IN WIND-TUNNEL EXPERIMENTS. THE WIND TUNNEL SUITABLE FOR DEPOSITION EXPERIMENTS WHICH IS REQUIRED FOR THIS PURPOSE IS AT PRESENT UNDER CONSTRUCTION AT THE INSTITUTE FOR RADIATION PROTECTION IN NUCLEAR TECHNOLOGY.
THE PROPOSED RESEARCH WORK REPRESENTS AN EXPANSION OF THE RESEARCH PROJECT "PRECIPITATION OF RADIOACTIVE MATERIALS ON VEGETATION, THE GROUND AND RAINDROPS DURING DIFFUSION IN THE ATMOSPERE" (ST.SCH.920) SUPPORTED BY THE FEDERAL MINISTER FOR THE INTERIOR OF THE FEDERAL REPUBLIC OF GERMANY AND CURRENTLY UNDERWAY AT THE INSTITUTE FOR RADIATION PROTECTION IN NUCLEAR TECHNOLOGY.
WITH THE TURBULENCE PARAMETERS OBTAINED BY MEANS OF THESE MEASUREMENTS, IT IS INTENDED, AS PART OF THE PROPOSED RESEARCH PROJECT, TO IMPROVE ACCURACY IN RESPECT OF THE DEPOSITION VELOCITIES DETERMINED SO FAR AS A FUNCTION OF THE VARIOUS RELEVANT PARAMETERS. ALL AVAILABLE MEASURED VALUES WILL BE TAKEN INTO ACCOUNT, AS HITHERTO, IN A COMPARISON WITH EXPERIMENTAL DATA.
TOGETHER WITH THE DEPOSITION MODELS ALREADY DEVELOPED AT THE TRAINING ESTABLISHMENT FOR RADIATION PROTECTION IN NUCLEAR TECHNOLOGY, ONE RESULT OF THE STUDIES WILL BE THE POSSIBILITY OF PREDICTING SUBSTANTIALLY MORE ACCURATELY THAN IS POSSIBLE TODAY THE DRY DEPOSITION OF RADIONUCLIDES BOUND TO AEROSOL PARTICLES AND OF RADIOIODINE ON THE BASIS OF THE METEOROLOGICAL AND OROGRAPHIC DATA AVAILABLE AT THE SITES OF NUCLEAR INSTALLATIONS. THE RESULTS CAN ALSO BE EXTRAPOLATED TO OTHER NON-RADIOACTIVE HARMFUL SUBSTANCES.

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Régime de financement

CSC - Cost-sharing contracts

Coordinateur

AACHEN UNIVERSITY OF TECHNOLOGY
Adresse
Templergraben 55
52056 Aachen
Allemagne

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