Improved global dispersion models for iodine-129 and carbon-14
166 Pages
English
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Improved global dispersion models for iodine-129 and carbon-14

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166 Pages
English

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ISSN 1018-5593
European Commission
duci
Cli
Improved global dispersion models for
iodine-129 and carbon-14
Report
EUR 15880 EN European Commission
nuclear science
and technology
Improved global dispersion models for
iodine-129 and carbon-14
J. G. Titley, T. Cabianca, G. Lawson, S. F. Mobbs, J. Simmonds
NRPB
Chilton, Didcot
Oxfordshire OX 11 ORQ
United Kingdom
Contract No FI2W-CT90-0008
Final report
Work performed as part of the European Atomic Energy Community's shared-cost programme (1990-94)
'Management and disposal of radioactive waste'
Task 5: 'Methods of evaluating the safety of disposal systems'
Directorate-General
Science, Research and Development
1995 EUR 15880 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 92-827-0090-9
© ECSC-EC-EAEC, Brussels · Luxembourg, 1995
Printed in Luxembourg Contents
Page
Introduction
1.1 Overview
1.2 Global dispersion models
Global models for 14C
2.1 Introduction
2.2 Review of existing models and data
2.2.1 Introduction
2.2.2 Parameter values
2.2.3 Implementation of existing 14C
on the NRPB computer system
2.2.4 Calculation of doses
Discussion of model results 2.2.5
2.3 Development of a new model
2.3.1 Introduction
2.3.2 Ocean section
Terrestrial section 2.3.3
2.3.4 Dose model
2.4 Results and discussion
2.5 Global climate change
2.5.1 Introduction
2.5.2 Fossil fuel burning
2.5.3 Cooling
2.5.4 Warming
Global models for 129l
3.1 Introduction
3.2 Review of models and data
3.2.1 Kocher's model
3.2.2 Smith and White's model
3.2.3 Fabryka-Martin's model
3.2.4 Data review
3.3 New model for global circulation of 129I
3.3.1 Introduction
3.3.2 Atmosphere
3.3.3 Oceans and ocean sediments
3.3.4 Soil and terrestrial biosphere
3.3.5 Groundwater
Sedimentary Rock 3.3.6
3.3.7 Dose calculation
3.4 Results and discussion
3.5 Climate change
Summary
4.1 14C model
4.1.1 Future work
4.2 129I model
References
5.1 14C global modelling
5.2 129I globalg
Acknowledgements Tables
2.1 A summary of the existing global circulation compartmental models from recent literature.
2.2 Parameter values for carbon models taken from the available literature.
2.3 A summary of runs undertaken on NRPB VAX computer (COMA solving routine) using
carbon models from the literature.
2.4 Determination of revised areas of the oceans for use in new model.
2.5 Tranfer of carbon between terrestrial biosphere and oceans by river.
2.6 Stable carbon compartment inventories for the new model.
2.7 Data for implementation of proposed new global carbon model using COMA, main version.
2.8 A summary of the model runs undertaken on NRPB VAX computer (COMA solving
routine) using the new NRPB model, constant total carbon background.
2.9 Natural 14C in exchangeable reservoirs predicted by the new global carbon model (C-14
natural production rate of 1.075 1015 Bq y"1) and taken from the literature.
2.10 Summary of bomb 14C inventories by ocean region as predicted by the new global carbon
model and as reported in the literature.
2.11 Time history of bomb 14C in the atmosphere and biosphere between 1950 and 1990
(deviation in 14C/Total Carbon from the no-bomb standard) predicted by the proposed
global carbon model and as reported from the literature.
2.12 Collective doses to Global and EC populations as a function of time as predicted by the
main version of the new global carbon model. Unit release of 1 TBq of C to the
atmosphere, atlantic surface, atlantic bottom and soil. Results for a constant total carbon
background are presented.
2.13 A summary of the model runs undertaken on VAX computer using the new NRPB model,
main version, with fossil fuel burning.
2.14 Collective doses to Global and EC populations as a function of time as predicted by the
main version of the new global carbon model. Unit release of 1 TBq of 14C to the
atmosphere, atlantic surface, atlantic bottom and soil. Results for a fossil fuel total carbon
background are presented.
2.15 Integrated collective doses to EC obtained in sensitivity anlyses for climate change (lTBq
release).
2.16 Integrated collective doses to world obtained in sensitivity analyses for climate change
(1 TBq release).
3.1 Review of concentrations of stable iodine in various materials adopted in global models for
circulation of 129I.
3.2 Parameters and their values used in the new model of global circulation of I.
3.3 Inventories and residence times of stable iodine adopted in the new model of global
circulations of 129I.
3.4 Fluxes adopted in the new model of global circulation of 129I.
3.5 Calculation of density and concentration of stable iodine in soil as adopted in the new
model for circulation of 129I.
3.6 Intake rates (g d"1) adopted in existing models and in the new model of global circulation
of129I.
3.7 World population (millions) by geographical areas.
IV 3.8 Parameter values used in the pathway analyses in existing models and in the new model
of global circulation of 129I.
3.9 Daily intake of iodine (micro-g d"1) assumed in existing models and in the new model of
global circulation of 129I.
3.10 Dosimetric data adopted in existing models and in the new models of global circulation of
129j
3.11 1-129 global circulation model. Comparison of collective effective doses (man Sv) to the
world population arising from a discharge of 1 TBq for 1 year to five different
compartments calculated using the new model, Kocher's model and Smith and White's
model.
3.12 1-129 global circulation model. Effect of 0.20% increase and of a 20% reduction
imprecipitation rate and runoff of surface waters of collective effective doses to the world
population arising from a discharge of lTBq for 1 year to 5 différend compartments.
Figures
2.1 A simple representation of global circulation models for carbon.
2.2 Global carbon model of Cannell and Hooper. Compartment inventories in g, fluxes
between compartments in g y of stable carbon.
2.3 Existing NRPB global carbon model. Compartment inventories in g of stable carbon,
fluxes between compartments in g y"1.
2.4 NCRP global carbon model as implemented. Compartment inventories in g of stable
carbon, fluxes between compartments in g y .
2.5 Carbon model of Nair as implemented. Compartment inventories in g of stable carbon.
2.6 The new NRPB global compartmental model.
2.7 Detailed view of the Antarctic Ocean part of the model.
3.1 Kocher's model for global circulation of 1-129.
3.2 Smith and White's model for global circulation of 1-129.
3.3 Fabryka-Martin's model for global circulation of 1-129.
3.4 New model for global circulation of 1-129.
3.5 1-129 global circulation model. Summary of collective effective doses to the world
population arising from a discharge of 1 TBq for 1 year to five different compartments.
Appendix A Inventories and doses calculated using existing 14C models.
Appendix Β s and doses calculated using the new 14C model.
Appendix C Inventories and doses calculated using the new 129I model. 1 Introduction
1.1 Overview
This report describes the development of improved global circulation models for I and
14C under contract number FI2W-CT90-0008 between the National Radiological Protection Board
(NRPB) and the European Atomic Energy Community represented by the Commission of the
European Communities (CEC). The project is within Task 5 "Methods of Evaluating the Safety of
Disposal Systems" of the CEC Programme on Radioactive Waste Management and Storage.
The work programme was divided into the following four tasks:
TASK 1 Consultation and literature search to identify models, their implementation on the
NRPB computer and comparison of their results.
TASK 2 Consultation and literature search for information on important processes in the
global circulation of carbon and iodine for parameter values for use in models identified in Task 1.
TASK 3 Review of models obtained in Task 1. Using information on important processes
and parameters, construction of 'state of the art' models.
TASK 4 Calculation of collective doses using the 'state of the art models' from task 3,
considering possible future climatic scenarios and quantification of possible ranges of results.
The rest of chapter 1 gives a general introduction to global models, chapter 2 describes the
work on 14C global models and chapter 3 describes the work on 129I global models.
1.2 Global circulation models
Globaln models are used to predict the general nature of the dispersion of
radionuclides whose longevity and mobility in the environment cause them to become globally
dispersed in time. Four radionuclides fall into this category, namely, 3H, 14C, 85Kr and 129I.
Compartmental global circulation models for each of these radionuclides have been developed
previously^. Tritium (3H) and Kr are too short-lived to be of concern for geologic disposal of
solid radioactive waste and are not considered within this contract. Global circulation models for
14C and 129I are used to predict the dispersion of these radionuclides over large space and time
scales. They are used principally in the calculation of collective doses to large populations over
long times. Each compartment in a global circulation model may represent a large part of an
environmental medium, in which the radionuclide is assumed to be mixed homogeneously and
instandy. Thus, the short term, local dispersion of the radionuclide cannot be adequately modelled
using a global circulation model. Local dispersion models are used to predict environmental
concentrations close to the release point at relatively short times and to predict the source term for
the corresponding global circulation model. Such local dispersion models are specific to the actual
point of release and the nature of the release, for example, to atmosphere, to a river or to the sea.
Descriptions of appropriate local dispersion models can be found elsewhere1^. 2 Global circulation models for carbon-14
2.1 Introduction
Carbon-14 occurs in the environment as a result of natural processes occurring in the upper
atmosphere, and from anthropogenic sources, such as nuclear weapons testing, and discharges from
the nuclear fuel cycle. Once produced carbon-14 circulates with stable carbon in a global cycle,
thereby becoming distributed throughout the biosphere and incorporated into all living organisms,
see Figure 2.1.
Carbon-14 has a half life of 5730 y, it is a weak beta emitter, and decays to 14N (stable).
The predominant pathway for natural 14C production is from 14N in the upper atmosphere by
capture of neutrons generated by cosmic rays. The rate of production is estimated to be in the range
1.0 1015 to 1.4 1015 Bq y"1 and has resulted in a total atmospheric burden of 1.4 1017 Bq, giving
rise to a specific activity of 0.222 Bq gC"1 3'4. The production rate variability is associated with
changes in output of energy from the sun over the 11 year sunspot cycle. Anthropogenic influences
include the release of 3.55 1017 Bq of 14C by detonation of thermonuclear devices, and lesser
emissions from the nuclear power cycle. Additionally, over the last 100 years the release of stable
carbon (as carbon dioxide) to the atmosphere by the combustion of fossil fuels has resulted in a
slight dilution of the specific activity of 14C in the atmosphere and biosphere3^.
The behaviour of 14C is considered to be analogous to stable carbon and all models
described in this section are dependant on this assumption.
2.2 Review of existing models and data
2.2.1 Introduction
The aim of the review was me identification of existing global dispersion models, the
gaining of information currently considered to be important in global carbon cycles, and obtaining
data on parameter values for use in the models. This was achieved by a literature search, using
available data bases, supplemented by contact with a number of individuals and organisations within
the EC and USA.
Two online data bases were searched:
1 Georefs (American Geological Institute, 1,000,000 records) which covers worldwide
technical literature on geology and geophysics.
2 IMS (International Nuclear Information System) which is a cooperative decentralized
information system set up by the International Atomic Energy Agency for identifying
publications relating to the peaceful applications of nuclear science.
In addition to these literature searches, the NRPB library data base was accessed and
searched. The fifteen most relevant models identified from the literature review are summarised in
Table 2.1. The models range in complexity from a simple 6 compartment model, to a detailed 146
compartment model.
Only those of NCRP3, Killough9, Nair12 and NRPB (Bush et al., 1983)13 include an
assessment of the dose to man arising from the global circulation of 14C.
A number of researchers working in the area of carbon cycling and global warming were
contacted in order to obtain current relevant information on the behaviour of carbon, including that
arising out of recent interest in the role of carbon dioxide on climate change.