Review of specific effects in atmospheric dispersion calculations. Volume 1, Final report

Directorate-General For Research And Innovation

Description

Nuclear energy and safety

Sujets

• Air pollution

Informations

• Publié par: DIRECTORATE-GENERAL-FOR-RESEARCH-AND-INNOVATION
• Nombre de lectures: 12
• Langue: English
• Poids de l'ouvrage: 26 Mo

Extrait

Commission of the European Communities
nuclear science
and technology
Review of specific effects in
atmospheric dispersion calculations
Volume 1 Commission of the European Communities
nuclear science
and technology
Review of specific effects in
atmospheric dispersion calculations
B.Y. Underwood, P.J. Cooper, N.J. Holloway, G.D. Kaiser, W. Nixon
United Kingdom Atomic Energy Authority (UKAEA)
Safety and Reliability Directorate
Harwell
United Kingdom
Volume 1
Contract No SR011-80 UK (B)
Final report
Directorate-General
Science, Research and Development
1984 EUR 8935 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Information Market and Innovation
Bâtiment Jean Monnet
LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting
on behalf of then 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, 1984
ISBN 92-825-4182-7 Catalogue number:1
© ECSC-EEC-EAEC, Brussels · Luxembourg, 1984
Printed in Belgium CONTENTS
VOLUME 1 : Chapter 1 to 3
VOLUME 2 :r 4 to IO
Author Page
Β. Y. underwood S-l Summary Document
G. D. Kaiser 1-1 Ch 1 Plume Rise in Nuclear Safety Studies
Β. Y. Underwood 2-1 Ch 2 Dry Deposition
Β. Y.d 3-1 Ch 3 Wetn
Ch 4 Atmospheric Dispersion in Urban
Environments N. J. Holloway 4-1
Ch 5 Topographical Effects in Nuclear Safety
Studies - a Review P. J. Cooper 5-1
Ch 6 Coastal Effects and Transport over Water
W. Nixon 6-1
Ch 7 Time-Varying Meteorology in Consequence
Assessment
Β. Y. Underwood 7-
Ch 8 Building Effects in Nuclear Safety
Studies - a Review
P. J. Cooper 8-1
Ch 9 Effect of Variations in Mixing Height
on Atmospheric Dispersion
Β. Y. Underwood 9-1
Ch 10 The Effect of Turning of the Wind with
Height on Lateral Dispersion
Β. Y. Underwood 10-1
III IV REVIEW OF SPECIFIC EFFECTS IN
ATMOSPHERIC DISPERSION CALCULATIONS
SUMMARY DOCUMENT
Β.Y. UNDERWOOD
Safety and Reliability Directorate
S-l S-2 1 INTRODUCTION
This summary document serves as an overview of the material prepared in
fulfilment of contract SR011-80UK(B) entitled "Review of Specific Effects in
Atmospheric Dispersion Calculations". The Technical Annex of the contract
listed 13 topics (see Table 1) to be included in the review exercise, at the
same time recognising that there was some overlap amongst topics. The
approach adopted by SRD has resulted in the production of 10 separate
reviews and the relationships between specified topics and review chapters
is sketched in Table 1. It should be noted that the pertinent aspects of
"terrain roughness", "transport over water" and "mesoscale problems" are
covered in existing reviews: in particular it was agreed that the definition
of 'mesoscale' intended in the original specification was 10-100km, the main
problems of interest being topographical effects, coastal effects, urban
effects, time varying meteorology and spatial variation of precipitation.
A principal motivation for reviewing these topics is the recognition that
the 'first generation' of computer codes written to assess the consequences
of major reactor accidents accounts for the phenomena under consideration at
only a very rudimentary level, if at all. Many of the subject areas have
undergone considerable development in the last few years and the need for
up-to-date reviews was apparent. Although some of the technical areas have
been generally reviewed in the literature, the emphasis in this work has
been directed towards their impact on the calculation of reactor-accident
consequences and this has dictated to some extent the selection of material
included.
In general the reviews focus on the 0-100km range of downwind distance. In
practice, for a zero-threshold, linear dose-risk relationship, a large
contribution to the collective-dose integral used to calculate latent
cancers may arise from distances >100km, albeit from a large number of very
small individual doses. However, since the integration tends to attenuate
sensitivity to many details of the modelling, a common approach in
consequence assessment has been to make rather simplistic assumptions about
the > 100km range. The attention given to the longer range depends on which e parameters are considered most important, as discussed in
section 5.2.
The reviews have several uses: they serve as introductions to the subject
areas; they outline theoretical and experimental developments, particularly
recent ones; they act as reference documents, providing a copious source of
references for more detailed investigation of particular points; they raise
unresolved technical issues and attempt to indicate principal uncertainties;
they point to areas requiring further development.
Each of the reviews contains a summary and a detailed set of conclusions
which will not be duplicated here. However, in the following section a very
brief outline of the scope and principal conclusions of each review will be
given to set the scene for an overview of the study as a whole.
2 SCOPE AND PRINCIPAL CONCLUSIONS OF INDIVIDUAL REVIEWS
2.1 "Plume Rise in Nuclear Safety Studies" (G D Kaiser)
By agreement with the CEC this review was not as comprehensive as the
subject might appear to warrant; the reason for this was the existence of a
S-3 prior contract between the CEC and SRD specifically dealing with plume rise
(albeit in a fast-reactor content) which discussed many of the salient
points. However, the current review by Kaiser fills a gap in the literature
on plume rise in an accident-consequence context by raising important issues
besides those connected with the calculation of mean plume trajectory: ie
what are the conditions under which a buoyant plume can lift itself out of a
turbulent building wake; what is the ground-level concentration underneath a
rising plume; what are the factors determining the final height to which a
buoyant plume may rise? It is concluded that more attention has to be
directed to these questions if a reliable quantification of the impact of
plume rise is to be made. To this end SRD has commissioned wind-tunnel
investigations of "lift-off" and the concentrations under a rising plume;
preliminary results are described in the report, as are the results of
large-scale field trials (the METEOTRON project) in France.
The discussion in general reinforces the conclusions of the earlier contract
report, namely that
1. plume rise can in some circumstances bring about a considerable
reduction in the predicted number of early deaths and morbidities, and
2. the predicted reduction in the number of latent effects is much
less marked.
2.2 "Dry Deposition" (Β Y Underwood)
Previous assessments of reactor-accident consequences have shown significant
sensitivity of some consequence parameters to the magnitude of the dry
deposition velocity. The review first explains physical concepts associated
with the theory of dry deposition, including the resistance-chain analogy,
then goes on to review separately gas and particle deposition velocities
since the issue of what is the physico-chemical form of the principal
radionuclides released is not prejudged. Different surface types - smooth,
rough, water, urban - are treated separately, with the emphasis on
vegetative canopies. For gases the applicability of standard mass-transfer
correlations is assessed, and the importance of the surface-resistance
component highlighted. The extensive empirical data on iodine deposition to
grass are reviewed. For particles, theories of transfer to smooth surfaces
are described in some detail since this gives insight into the physical
mechanisms involved; however, it is also demonstrated that the micro-
roughness characteristics of natural surfaces have a strong effect on
deposition. It is shown how the net dependence on particle size results
from a number of different physical processes dominating in different size
regimes, leading to a characteristic minimum in the 0.1 - 1 μπι size range.
The review concludes that deposition velocity depends strongly on
characteristics of the released material, for example whether particle or
gas; particle size especially has a strong influence. This sensitivity
implies a need to better define source-term parameters. Secondly,
deposition velocity also depends strongly on surface characteristics
indicating perhaps that details of land usage may need to be incorporated
into consequence assessments. Not much is published on deposition in urban
environments. Recent filtration-type models for deposition to vegetative
canopies are promising and warrant further development. Finally, deposition
velocity depends on atmospheric conditions, although the dependence is not
usually dominant.
S-4