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Deposition of radionuclides, their subsequent relocation in the environment and resulting implications. Report

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ISSN 1018-5593 * * tir **European Commission radiation protection Deposition of radionuclides, their subsequent relocation in the environment and resulting implications European Commission radiation protection Deposition of radionuclides, their subsequent relocation in the environment and resulting implications J. Tschiersch, G. Frank, U. Hillmann, P. Jacob, R. Meckbach, H.G. Paretzke and F. Trautner GSF­Forschungszentrum für Umwelt und Gesundheit 85758 Oberschleißheim Germany J. Roed, K.G. Andersson and C. Lange Risø National Laboratory, MIL­114 4000 Roskilde Denmark Α. J. Η. Goddard and M. A. Byrne Imperial College of Science, Technology and Medicine London SW7 2BX United Kingdom J. Brown and J.A Jones National Radiological Protection Board Chilton, Didcot, Oxon ΟΧ11 ORQ United Kingdom K. Rybácek, J. Palágyi, S. Palágyi and M. Tomásek Institute of Nuclear Physics 18086 Prague 8 Czech Republic I. Navarcik, A. Mitro, V. Jansta, I. Datelinka and A. Cipáková Institute of Radioecology, j.s.c 04061 Kosice Slovak Republic P. Zombori and I.

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ISSN 1018-5593
* * tir
*
*
European Commission
radiation protection
Deposition of radionuclides, their subsequent
relocation in the environment and
resulting implications European Commission
radiation protection
Deposition of radionuclides, their subsequent
relocation in the environment and
resulting implications
J. Tschiersch, G. Frank, U. Hillmann, P. Jacob, R. Meckbach, H.G. Paretzke and F. Trautner
GSF­Forschungszentrum für Umwelt und Gesundheit
85758 Oberschleißheim
Germany
J. Roed, K.G. Andersson and C. Lange
Risø National Laboratory, MIL­114
4000 Roskilde
Denmark
Α. J. Η. Goddard and M. A. Byrne
Imperial College of Science, Technology and Medicine
London SW7 2BX
United Kingdom
J. Brown and J.A Jones
National Radiological Protection Board
Chilton, Didcot, Oxon ΟΧ11 ORQ
United Kingdom
K. Rybácek, J. Palágyi, S. Palágyi and M. Tomásek
Institute of Nuclear Physics
18086 Prague 8
Czech Republic
I. Navarcik, A. Mitro, V. Jansta, I. Datelinka and A. Cipáková
Institute of Radioecology, j.s.c
04061 Kosice
Slovak Republic
P. Zombori and I. Fehér
KFKI Atomic Energy Research Institute
1525 Budapest
Hungary
Final Report
Directorate­General
Science, Research and Development
1995 EUR 16604 EN Published by the
EUROPEAN COMMISSION
Directorate-General XIII
Telecommunications, Information Market and Exploitation of Research
L-2920 Luxembourg
LEGAL NOTICE
Neither the European Commission nor any person acting on behalf of
the Commission is responsible for the use which might be made of the
following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1995
ISBN 92-827-4903-7
© ECSC-EC-EAEC, Brussels · Luxembourg, 1995
Printed in Germany Summary
The research programme "Deposition of artificial radionuclides, their subsequent relocation in the
environment and implications for radiation exposure" was initiated by the Commission of the
European Communities under the Contract FI3P-CT92-0038. The main objective of the
programme was to improve, where necessary, the models and their parameterizations used in
estimating the intensity and spatial distribution of deposited radionuclides and the total impact of
such deposits in assessments of the accidental releases of radioactivity. For that purpose several
experimental studies on specific relevant problems were performed and models were developed.
The results of the experimental programmes were reviewed and considered for incorporation into
nuclear accident consequences assessment codes. The direct link between experimental studies,
model development and the improvement of accident consequences assessment codes was one of
the main features of the project.
Field studies have been undertaken at GSF with the aim of improving the characterisation of the
wet deposition process of radionuclides by appropriate parameters. In addition to the
measurement of the particle size distribution, special emphasis was given to the simultaneous
determination of the size distribution of the rain drops. A newly developed rain drop spectrometer
(pluvio-spectrometer) was used for this purpose. It was found that the scavenging process is
strongly influenced by the rain drop size distribution. The variation of scavenging rate with particle
size is small when many of the rain drops are large. However, the g rate varies much
more with particle size when small rain drops are predominating. A comparison with values
calculated in accident consequence codes showed that, in general, at lower precipitation intensities
the scavenging efficiency is underestimated, but at higher intensities it tends to be overestimated. It
is proposed to develop a parameterization based on particle and rain drop size distribution rather
than on rain intensity only. Deposition by fog proved to be a very efficient path for deposition.
High deposition velocities have been measured particularly for large and hygroscopic aerosol
particles.
The process of aerosol deposition on indoor surfaces has implications for human exposure to
particulate contaminants of both outdoor and indoor origin. Indoor deposition rates have been
determined by monitoring the decay of tracer aerosol in three Danish and one British house by
Risø and Imperial College. Monodisperse aerosols from 0.5 to 6.5 μπι in size were labelled with
dysprosium and released in the houses. Sequential air samples were analysed by neutron
activation. The results were consistent with increasing deposition velocities for increasing particle
size and increasing degree of furnishing. An empirical formula was found by a power regression of
the deposition velocity, vd, as a function of the aerodynamic diameter of the particles, dp :
Vd = 1.23 · 10"4 · (dp in μπι)065 ms'1. Using this formula dose reduction factors were calculated as a
function of particle size.
It has long been recognised that a relationship exists between the occurrence of some adverse
health effects and the deposition of airborne contaminants onto skin. In order to extend the
database for aerosol n velocities to skin, and also to hair and clothing, comprehensive
measurements were carried out by Imperial College and Risø working in close collaboration. It
was found that deposition velocities to skin are at least one order of magnitude higher than to
internal building surfaces. Considerable variability exists in the values measured, partially
III attributable to differences in the volunteers. It is suggested that the deposition velocity of aerosol
particles of micrometer dimensions to skin are in the order of 10"2 m/s. Tests with heated and
unheated aluminium cylinders indicate that the measured deposition velocity was higher to the
heated surface. This finding demonstrates that body heat may be responsible for a significant
proportion of the differences between the deposition velocity values observed to human and inert
subjects. The volunteers differ in their arm-hair growth. More aerosol particles were deposited on
a hairy arm than on a non-hairy arm, indicating the strong influence of the surface roughness on
aerosol deposition velocities. Hair deposition has not been seen to differ significantly from skin
deposition; however, a satisfactory protocol for determining hair surface is still under
development. A subject which must also be considered when assessing radiological risk due to
aerosol deposition on the body is the efficiency of removal of the deposited material through
active decontamination procedures. The removal efficiency for silica particles was found to be
higher by washing than by wiping. The mean decontamination efficiency was about 52%.
Following caesium deposition from the atmosphere to the ground, fields with undisturbed caesium
depth distributions are a major source for the external exposure of the population. Two methods
for the determination of the gamma dose rate in air due to caesium distributions in soil have been
applied by GSF, Risø, INP Prague and IR Kosice. The first method is soil sampling and laboratory
measurements, the second method is the peak-to-valley evaluation of in situ gamma-ray spectra, a
method that has been developed in the framework of this project. From the obtained results,
gamma dose rates in air due to caesium in the soil have been calculated. These data have been
analytically approximated to allow an easy use of the results in external dose assessment models.
The new analytical approximations were compared to former approximations utilising
measurement results from Southern Bavaria after the Chernobyl accident and from the New York
area after the atmospheric weapons test fallout. The new approach gives a better approximation to
the measured data at medium and long times after deposition.
Weathering of radioactive substances in urban areas was studied, and the calculation of location
factors in urban dry deposition scenarios was performed by Risø and GSF. The time series of
measurements of weathering on urban surfaces in the town of Gävle (Sweden) now spans over
almost a decade and has provided a reference against which existing models can be validated.
Weathering measurements were also made in other parts of Europe (Bavaria and Russia) and the
results were found to agree very well. The weathering effect on radiocaesium on paved surfaces in
Bavaria since the Chernobyl accident has been followed continually from the early phase.
Location factors were calculated for various dry deposition scenarios in houses offering different
shielding, partly based on experimental data, and it was established that indoor deposition may
have great influence on the location factors. Other calculations based on in situ gamma
spectrometry in Bavarian environments (mainly affected by wet deposition) gave location factors
which were comparable to those found by the first approach for a medium shielded house.
The behaviour of long-lived radionuclides in the atmosphere, (their concentration in ground level
air, wet and dry deposition and resuspension) was studied. A considerable amount of experimental
data based on two larger-scale nuclear accidents (Chernobyl and Goiânia) was collected during the
contract period and substantial contributions were provided by Risø, GSF and the PECO partners
(INP Prague, IR Kosice and AERI Budapest).
These contributors provided data on 137Cs activity concentration in ground level air, both for the
case of a local contamination (GSF for Goiânia) and for global contamination (PECO participants
and Risø for the Chernobyl accident). Data are available for atmospheric 90Sr from the IR. The
IV concentration of 7Be in the air was measured by IR, INP, AERI and Risø for comparison with
137Cs data. The overall trend for airborne 137Cs concentration of Chernobyl origin is a slight
decrease with time in Central Eastern Europe. The same trend was found for the 137Cs data on the
Goiânia local contamination accident site. Seasonal variation was observed, atmospheric ' Cs
being higher in the winter time than during the summer. In contrast, cosmogenic 7Be was found to
vary in a different way, having higher values in the summer and minima during winter. Seasonal
changes in 137Cs data seem to be strongly related with the rainfall rate in Goiânia. A somewhat
different seasonality was found for 90Sr, with maxima in winter and summer and minima in spring
and autumn.
Regular measurement of airborne l37Cs in the long term provides a good basis for deriving the
resuspension factor K as a function of time. A value of 10"9 m' in recent years (a level slowly
decreasing from about 2 · 10~8 m"1 in 1986) was found to be typical in Prague. This value (K
around 2 · 10"9 m') and trend were also confirmed on a similar surface contamination area (5.4
kBq/m2) in Budapest and in Risø (K around IO'9 m"1 since 1991). The experimental data (also in
the order of 10"9 - 10"8 m' ) measured in Goiânia show that the resuspension and deposition of
137Cs is a local phenomenon which is, however, somewhat dependent on the extent of the primary
deposition. These experimental values were compared with the K parameters used by the codes
COSYMA and RODOS.
The dominance of water solubility of 137Cs, observed by INP in air samples taken in the early-
phase after the Chernobyl accident, later changed towards a higher proportion of the insoluble
fraction. This is explained by the penetration of the soluble fraction into deeper soil layers making
the soluble fraction less available for resuspension. Recently IR found that there is a seasonal
variation in the solubility of airborne 137Cs. The prevailing form is water-soluble in the winter
months, acid-soluble in the summer period and insoluble in the end of spring and start of summer.
90Sr is mostly insoluble in the summer while the acid-soluble form is dominant for the other
seasons.
A different deposition pattern was observed for the radionuclides, Cs and Be. Cs
measurements indicated high dry deposition velocities and showed little (INP) or no (Risø)
correlation with precipitation. The high deposition velocities, from 0.02 to 1 ms"1, correspond to
the sedimentation velocity of rather large particles, 24 to 173 μπι. Estimating the size of
resuspended particles in Goiânia also showed that a significant fraction of the activity was present
in large particles, dp > 15 μπι. For 7Be dry deposition velocities were found to be much smaller,
around 5 · 10"4 ms" , and a strong dependence of deposition rate on precipitation was observed. In
summary, 7Be showed a deposition pattern similar to that of a long-range transported
radionuclide.
In models used in the assessment of the consequences of accidental releases of radioactivity only limited
effort had been directed to the behaviour of radioactive fallout deposited in an urban environment prior
to the Chernobyl accident. The need has emerged for contingency strategies which enable the
consequences of radioactive contamination of large urban areas to be identified and dealt with as early
as possible following contamination. The URGENT (URban Gamma Exposure Normative Tool) and
the PARATI (Program for the Assessment of RAdiological consequences in a Town and of
Intervention after a radioactive contamination) models have been developed by Risø and GSF in order
to facilitate the decision-making in such cases. Experimental data is used for URGENT to describe the
system of retention/migration loss processes which might occur on outdoor surfaces in an urban
environment contaminated with radioactive material. The resulting gamma doses can then be calculated
for four different urban or suburban environments using dose conversion factors. The model is
restricted to cover the behaviour of the single most important radionuclide concerning external dose from urban contamination - namely 137Cs. Further, a semi-empirical model has been introduced to
estimate the relative importance of radiocaesium deposition on internal surfaces of buildings. Also
described is a different model for radiological assessments in urban areas, PARATI, which has been
developed for similar purposes. The basic functions of the PARATI code are to estimate the radiation
exposures for different groups of people as a function of time after an accident with the indication of the
fractional contributions to this exposure from each pathway, and to indicate the feasible
countermeasures and their relative effectiveness regarding reduction of doses.
An important objective of the programme, which has been undertaken by NRPB, has been to review
and consider the results from the experimental research with a view to their future incorporation into
models. The current models, which are used for describing deposition and relocation of material in
urban and rural areas for the estimation of doses and risks used in the COSYMA code for probabilistic
risk assessment and in the RODOS code for real time emergency response have been described. The
available data from the experimental research carried out under this programme and the current status
of research in this area were also reviewed in the context of the current models. The contractors, as a
whole, have reviewed the adequacy of the current models for their given purpose and how the data
from this experimental research programme could be used to improve or support the current modelling
approach. This review and recommendations for changes in the models are described. As a
consequence of the review some parameters used in COSYMA have been revised and
recommendations are given where future research is required.
VI Contents
SUMMARY ΠΙ
INTRODUCTION1
1.DEPOSITIONOFATMOSPHERIC AEROSOL BY RAIN AND FOG3
1.1BELOW-CLOUDAEROSOL SCAVENGING3
1.2DEPOSITIONBYFOG8
1.3FURTHERNEEDSOFRESEARCH10
1.4 REFERENCES11
2. INDOOR DEPOSITION MEASUREMENTS AND IMPLICATIONS
FOR INDOOR INHALATION DOSE 13
Abstract13
2.1 INTRODUCTION13
2.2 EXPERIMENTAL TECHNIQUE15
2.2.7 The particles15
2.2.2 Summary of experimentaltechnique16
2.3 RESULTS AND DISCUSSION17
2.3.1 Empirical modelsforindoordeposition19
2.3.2 A simple modelfortheprotectivevalueofahouse19
2.3.4 Temporal variationsoftheIndoor/Outdoorratio21
2.4 REFERENCES 22
3.AEROSOLDEPOSITION ON SKIN, HAIR AND CLOTHING 25
3.1INTRODUCTION25
3.2EXPERIMENTALMETHODOLOGY25
3.2.1Selectionoftest subjects25
3.2.2oftest aerosol26
3.2.3Aerosolmassbalance tests27
3.3EXPERIMENTALCONFIGURATION28
3.4 L RESULTS29
3.5 RECOMMENDATIONS FOR FUTURE RESEARCH 33
3.6 REFERENCES34
4. RADIONUCLDDE DISTRIBUTIONSINUNDISTURBED SOIL AND
RELATED GAMMADOSERATESINAIR35
4.1 CAESIUM AND STRONTIUMMIGRATIONINCOLUMNEXPERIMENTS35
4.2 MEASUREMENTS OF CAESIUM DISTRIBUTIONS BY SOIL SAMPLING 36
4.3 ANALYTICAL APPROXIMATION OF CAESIUMDISTRIBUTIONSINSOIL38
4.4//vsm/DETERMINATION OF CAESIUM DISTRIBUTIONSINSOIL41
4.5 GAMMA DOSE RATES IN AIR 44
4.6 REFERENCES46
5. WEATHERINGOF,37CSONVARIOUS SURFACESININHABITED AREAS
AND CALCULATEDLOCATION FACTORS47
INTRODUCTION47
5.1 MEASUREMENTSOFWEATHERINGIN GÄVLE47
5.2 SOFGIN THE FORMER SOVIET UNION 51
5.3 SOFWEATHERINGIN SOUTHERN BAVARIA51
5.4 LOCATIONFACTORCALCULATIONSFOR '37CSANDI3IIFORURBANDRY DEPOSITION SCENARIOS52
5.5 REFERENCES55
VII 6. RESUSPENSION OF DEPOSITED MATERIAL 59
INTRODUCTION 59
6.1 SUMMARY59
6.2137CsINGROUND LEVEL AIROFBUDAPEST61
6.2.1Discussion61
6.3l37CsINTHE ATMOSPHERE OFPRAGUE64
6.3.1Results64
6.4CHEMICALFRACTION OF RADIOACTIVE CAESIUM IN ATMOSPHERIC AEROSOL IN PRAGUE
AFTERTHECHERNOBYL ACCIDENT68
6.4.1Results69
6.5SPECIATION OF DEPOSITED ARTIFICIAL RADIONUCLIDES 71
6.5.1Results71
6.5.2Discussion·76
6.6RESUSPENSION STUDIES IN GOIÂNIA,BRAZIL77
6.7 RADIONUCLIDE RESUSPENSIONANDMIXEDDEPOSITIONAT DIFFERENT HEIGHTS 78
6.8 REFERENCES81
7. MODELLING OF THE RADIOLOGICALIMPACT OF A DEPOSIT
OF ARTIFICIAL RADIONUCLIDESININHABITED AREAS83
INTRODUCTION 83
7.1METHODSFORCALCULATION OF DOSES FROM OUTDOOR SOURCES 84
7.1.1TheURGENTmodel84
7.1.2ThePARATImodel86
7.2METHODFORCALCULATION OF DOSE FROM INDOORSOURCES88
7.3CALCULATIONRESULTS88
7.4REFERENCES93
8.REVIEWOFCURRENTEXTERNAL DOSE MODELSANDRECENT
EXPERIMENTALRESEARCH ON THE DEPOSITION AND SUBSEQUENT
RELOCATION OF ARTIFICIAL RADIONUCLIDES 95
8.1 INTRODUCTION 95
8.2REQUIREDCOMPLEXITYOF MODELS96
8.3EXISTINGMODELSFORTHE DEPOSITED Γ DOSEINRURALANDURBANAREAS96
8.4MODELSUSEDINCOSYMA AND RODOS97
8.4.1Deposition97
8.4.2 Data libraries for deposited γ dose99
8.4.2.1 COSYMA99
8.4.2.2 RODOS99
8.4.2.3 Further developments to deposited γ dose data libraries 100
8.4.3 Shielding of groups of the population100
8.4.3.1 COSYMA 100
8.4.3.2RODOS101
8.4.4Resuspension102
8.4.5Decontamination102
8.5REVIEWOFSUB-PROCESSMODELLING IN LIGHTOFCURRENTDATAANDRESEARCH UNDER THIS CONTRACT...103
8.5.1Deposition103
8.5.1.1Parameterisationof dry deposition103
8.5.1.2Effectoffogondry deposition103
8.5.1.3Indoordepositionand air concentrations104
8.5.1.4Depositiontoskinand clothes105
8.5.1.5Theneedtoconsider deposition to trees in ACA codes 106
8.5.1.6 Wet deposition107
8.5.2 Resuspension107
8.5.3 Weathering 108
8.5.3.1SoilMigration108
8.5.3.2Weatheringfromurban surfaces108
8.6RECOMMENDATIONSFORFURTHER WORK109
8.7REFERENCES109
ACKNOWLEDGEMENT113
VIII