Radionuclide behaviour in the natural environment docx

Geological repository systems for safe disposal of spent nuclear fuels and radioactive waste ISBN 978-1-84569-542-2 The long-term safety of spent nuclear fuel and radioactive waste mater

Radionuclide behaviour in the natural environment

Geological repository systems for safe disposal of spent nuclear fuels and radioactive waste

(ISBN 978-1-84569-542-2)

The long-term safety of spent nuclear fuel and radioactive waste materials must be assured without active human oversight, based on the requirement that we do not pass the burden of nuclear waste onto future generations Geological disposal systems and technology, utilising both natural geological barriers and engineered barrier systems, have been developed to isolate nuclear wastes from the human environment This book critically reviews state-of-the-art technologies, scientific methods and engineering practices directly related to the design, operation and safety of geological repositories.

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The potential development of any nuclear power programme requires a rigorous justification process built upon an objective infrastructure, reviewing the substantial regulatory, economic and technical information required to appropriately decide upon implementation of such a long-term commitment Both new entrants and those countries wishing to renovate their nuclear fleets after a moratorium will need

to develop and apply appropriate infrastructures to review the justification of the potential use of nuclear power This book provides a comprehensive review of the infrastructure and methodologies required to justify the implementation of nuclear power programmes in any country choosing to review this path.

Handbook of advanced radioactive waste conditioning technologies

(ISBN 978-1-84569-626-9)

Radioactive wastes are generated from a wide range of sources presenting a variety

of challenges in dealing with a diverse set of radionuclides of varying concentrations Conditioning technologies are essential for the encapsulation and immobilisation

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Woodhead Publishing Series in Energy: Number 42

Radionuclide

behaviour in

the natural

environment

Science, implications and lessons for

the nuclear industry

Edited by Christophe Poinssot and Horst Geckeis

Oxford Cambridge Philadelphia New Delhi

www.woodheadpublishingonline.com

Woodhead Publishing, 1518 Walnut Street, Suite 1100, Philadelphia, PA 19102-3406, USA Woodhead Publishing India Private Limited, G-2, Vardaan House, 7/28 Ansari Road, Daryaganj, New Delhi – 110002, India

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First published 2012, Woodhead Publishing Limited

© Woodhead Publishing Limited, 2012 The publisher has made every effort to ensure that permission for copyright material has been obtained by authors wishing to use such material The authors and the publisher will be glad to hear from any copyright holder it has not been possible to contact.

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Contributor contact details xiii Woodhead Publishing Series in Energy xix

1 Overview of radionuclide behaviour in the natural

C P oinssot , French Nuclear and Alternative Energies Commission

(CEA), France and H G eckeis , Karlsruhe Institute of Technology

2 Fundamentals of aquatic chemistry relevant to

T n eumann , Karlsruhe Institute of Technology (KIT), Germany

3 Aquatic chemistry of the actinides: aspects relevant

M a ltmaier , Karlsruhe Institute of Technology (KIT), Germany

and T V ercouter , French Alternative Energies and Atomic Energy

Commission (CEA), France

4 Aquatic chemistry of long-lived mobile fission and

activation products in the context of deep

P E r eiller , French Nuclear and Alternative Energies

Commission (CEA), France and G b uckau , Institute for

Transuranium Elements, Germany

6 Impacts of microorganisms on radionuclides in

contaminated environments and waste materials 161

A J F rancis , Pohang University of Science and Technology,

South Korea and Brookhaven National Laboratory, USA

6.6 Biotransformation of fission and activation products 196

7 Hydrogeological features relevant to radionuclide

E l edoux , P G oblet and d b ruel , Mines-ParisTech, France

7.5 Groundwater flow equations for aquifer systems 2467.6 Solving the flow equations for aquifer systems 249

8 Radionuclide retention at mineral–water interfaces in

M m arques F ernandes and B b aeyens , Paul Scherrer Institut,

Switzerland and C b eaucaire , French Alternative Energies and

Atomic Energy Commission (CEA), France

8.6 Acknowledgements 288

9 Radionuclide migration: coupling transport and

J c arrera , C a yora , Institute of Environmental Assessment and

Water Research (IDAEA-CSIC), Spain, M W s aaltink , Technical

University of Catalonia (UPC), Spain and M d entz , Institute of

Environmental Assessment and Water Research (IDAEA-CSIC),

Spain

10 Impact of colloidal transport on radionuclide migration

A B k erstinG , Lawrence Livermore National Laboratory, USA

11 Natural analogues of nuclear waste repositories:

studies and their implications for the development of

L d uro and J b runo , Amphos 21 Consulting S.L., Spain

12 Studying radionuclide migration on different scales:

the complementary roles of laboratory and in situ

l V an l oon and m G laus , Paul Scherrer Institut, Switzerland

and C F erry and C l atrille , French Alternative Energies and

Atomic Energy Commission (CEA), France

transport of radionuclides in non-consolidated porous

13 Radionuclide transfer processes in the biosphere 484

e a nsoborlo , French Nuclear and Alternative Energies

Commission (CEA), France and C a dam -G uillermin , French

Institute for Radiological Protection and Nuclear Safety (IRSN),

France

Part III Environmental impact and remediation 515

14 Modelling radionuclide transport in the environment

M t horne , Mike Thorne and Associates Limited, UK

15 Quantitative assessment of radionuclide migration

from near-surface radioactive waste burial sites: the waste dumps in the Chernobyl exclusion zone as an

a m artin -G arin , n V an m eir and c s imonucci , French Institute for Radiological Protection and Nuclear Safety (IRSN), France,

V k ashParoV , Ukrainian Institute of Agricultural Radiology

(UIAR/NUBiP), Ukraine and D b uGai , Institute of Geological

Sciences (IGS), Ukraine

16 Remediation of sites contaminated by radionuclides 601

B J m erkel and M h oyer , TU Bergakademie Freiberg, Germany

17 Safety assessment of nuclear waste repositories: a

J b runo , and A d elos, University of Catalonia, Spain

17.5 Gaps in understanding and the qualification and

quantification of the safety assessment (SA) models 689

Editors and Chapter 1

Professor C Poinssot

French Nuclear and Alternative

Energies Commission (CEA)

Nuclear Energy Division

Department of Radio Chemistry

Karlsruhe Institute of Technology (KIT)

Adenauerring 20 b

76131 KarlsruheGermany

E-mail: neumann@kit.eduChapter 3

E-mail: marcus.altmaier@kit.edu

(* = main contact)

T Vercouter

French Alternative Energies and

Atomic Energy Commission

(CEA)

Nuclear Energy Division

DEN, DANS, DPC, SEARS,

A Abdelouas* and B Grambow

École des Mines de Nantes –

French Alternative Energies and

Atomic Energy Commission

(CEA)

Nuclear Energy Division

Centre d’Étude de Saclay

Joint Research CentreHermann-von-Helmholtz-Platz 1

76344 Eggenstein-LeopoldshafenGermany

E-mail: Gunnar.Buckau@ec.europa.eu

On leave from

Institut für Nukleare EntsorgungKarlsruhe Institute of Technology (KIT)

P.O Box 3640

76021 KarlsruheGermany

Chapter 6

A J FrancisDivision of Advanced Nuclear Engineering

Pohang University of Science and Technology

PohangSouth Korea

and

Environmental Sciences Department

Brookhaven National LaboratoryUpton

NY 11973-5000USA

E-mail: francis@bnl.gov

xvContributor contact details

Laboratory for Waste Management

Paul Scherrer Institut

French Alternative Energies and

Atomic Energy Commission

(CEA)

Centre d’Étude de Saclay

Department of Physics and

Calle Jordi Girona 18–26

08034 BarcelonaSpain

E-mail: jcrgeo@idaea.csic.es; jesus.carrera.ramirez@gmail.com

M W SaaltinkDepartment of Geotechnical Engineering and Geosciences Technical University of CataloniaSpain

Chapter 10

A B KerstingGlenn T Seaborg InstitutePhysical and Life SciencesLawrence Livermore National Laboratory

L-231 P.O Box 808Livermore

CA 94550 USA

E-mail: Kersting1@LLNL.govChapter 11

L Duro* and J BrunoAmphos 21 Consulting S.L

P Garcia I Faria 49–51, 1-1

08019 BarcelonaSpain

E-mail: Lara.duro@amphos21.com

Chapter 12

L Van Loon* and M Glaus

Laboratory for Waste Management

Paul Scherrer Institut

5232 Villigen

Switzerland

E-mail: luc.vanloon@psi.ch

C Ferry and C Latrille

French Alternative Energies and

Atomic Energy Commission

French Alternative Energies and

Atomic Energy Commission

(CEA)

Nuclear Energy Division

Department of Radio Chemistry

PRP-ENV/SERIS/LECODivision for Research and Expertise in Environmental Risks

Bâtiment 186Cadarache, BP 3

13115 Saint-Paul-lez-Durance Cedex

France

E-mail: Christelle.adam-guillermin@irsn.fr

Chapter 14

M ThorneMike Thorne and Associates Limited

Quarry CottageHamsterleyBishop Auckland DL13 3NJUK

E-mail: MikeThorneLtd@aol.comChapter 15

A Martin-Garin*

French Institute for Radiological Protection and Nuclear Safety (IRSN)

Bâtiment 186Cadarache BP3 13115 Saint-Paul-lez-Durance Cedex

France

E-mail: arnaud.martin-garin@irsn.fr

xviiContributor contact details

N Van Meir and C Simonucci

French Institute for Radiological

Protection and Nuclear Safety

09596 Freiberg/Sa

Germany

E-mail: merkel@geo.tu-freiberg.deChapter 17

J Bruno and A Delos*

University of CataloniaParc Tecnològic del VallésCerdanyola

08290 BarcelonaSpain

E-mail: jordi.bruno@amphos21.com; anne.delos@amphos21.com

1 Generating power at high efficiency: Combined cycle technology for sustainable energy production

Eric Jeffs

2 Advanced separation techniques for nuclear fuel reprocessing and radioactive waste treatment

Edited by Kenneth L Nash and Gregg J Lumetta

3 Bioalcohol production: Biochemical conversion of lignocellulosic biomass

Edited by K W Waldron

4 Understanding and mitigating ageing in nuclear power plants: Materials and operational aspects of plant life management (PLiM)

Edited by Philip G Tipping

5 Advanced power plant materials, design and technology

Edited by Dermot Roddy

6 Stand-alone and hybrid wind energy systems: Technology, energy storage and applications

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Woodhead Publishing Series in Energy

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Edited by John D Sørensen and Jens N Sørensen

utilisation

Edited by M Mercedes Maroto-Valer

17 Oxy-fuel combustion for power generation and carbon dioxide (CO 2 ) capture

Edited by Ligang Zheng

18 Small and micro combined heat and power (CHP) systems:

Advanced design, performance, materials and applications

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19 Advances in clean hydrocarbon fuel processing: Science and technology

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20 Modern gas turbine systems: High efficiency, low emission, fuel flexible power generation

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28 Infrastructure and methodologies for the justification of nuclear power programmes

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34 Handbook of metropolitan sustainability: Understanding and improving the urban environment

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36 Nuclear decommissioning: Planning, execution and international experience

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42 Radionuclide behaviour in the natural environment: Science, implications and lessons for the nuclear industry

Edited by Christophe Poinssot and Horst Geckeis

43 Calcium and chemical looping technology for power generation and carbon dioxide (CO 2 ) capture: Solid oxygen- and CO 2 -carriers

P Fennell and E J Anthony

44 Materials ageing and degradation in light water reactors:

Mechanisms, modelling and mitigation

Edited by K L Murty

45 Structural alloys for power plants: Operational challenges and high-temperature materials

Edited by Amir Shirzadi, Rob Wallach and Susan Jackson

46 Biolubricants: Science and technology

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47 Wind turbine blade design and materials: Improving reliability, cost and performance

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48 Radioactive waste management and contaminated site clean-up: Processes, technologies and international experience

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xxiiiWoodhead Publishing Series in Energy

49 Probabilistic safety assessment for optimum nuclear power plant life management (PLiM): Theory and applications of reliability analysis methods for major power plant components

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50 Coal utilization in industry

Edited by D G Osborne

51 Coal power plant materials and life assessment: Developments and applications

Edited by Ahmed Shibli

Edited by Angelo Basile

56 Handbook of membrane reactors Volume II: Industrial applications and economics

Edited by Angelo Basile

57 Alternative fuels and advanced vehicle technologies: Towards zero carbon transportation

Edited by Richard Folkson

58 Handbook of microalgal bioprocess engineering

Christopher Lan and Bei Wang

59 Fluidized-bed technologies for near-zero emission combustion and gasification

Edited by Fabrizio Scala

During my career, some 35 years, there has been a growing realization that the goal of successful nuclear waste management and the final disposal of long-lived radionuclides can only be attained by a thorough understanding

of the behavior of key, technogenic radionuclides in the environment Within

a nuclear reactor, these radionuclides are created by fission, neutron capture

activation nuclear reactions These reactor-created nuclides in used fuel or reprocessed waste are the ‘stuff’ that is destined for deep geologic disposal Lesser amounts of radioactivity may be released as nuclear materials are enriched for the production of new nuclear fuel or by reprocessing of used fuel to reclaim fissile nuclides Still, the major potential for the release of radioactivity is over the long periods envisioned for geologic disposal In this regard, the interface between the nuclear fuel cycle and the accessible environment is the geologic repository (see figure overleaf) Thus, the final evaluation of risk depends on the behavior of key radionuclides as they are disposed of and potentially released from a geologic repository These processes are the subject of this volume

The good news is that due to radioactive decay, the inventory of these radionuclides changes over time, and for long-lived radionuclides, the list

is rather short (see Table 1.1 in Chapter 1) The complicating news is that each radionuclide has its own geochemical cycle with different means

of release, transport, and finally, dilution or concentration This volume provides a detailed, and much needed, compilation of what is known about the behavior of these radionuclides Indeed, this volume carries the reader through a detailed discussion of the geochemistry of key radionuclides, their transport in solution or as colloids, and finally, through the vectors for human exposure and the calculation of dose and risk This final step is well illustrated by a quantitative assessment of radionuclide migration at contaminated sites, such as at Chernobyl Thus the organization and content of this volume will be essential to scientists and engineers in the nuclear waste

‘management’ business, and indeed, to environmental scientists concerned with radioactivity in the environment

Schematic illustration of the interface of the nuclear fuel cycle with the geochemical and hydrological cycles The geological

repository is at the interface between these two cycles The nuclear fuel cycle works on a time-scale of tens of years, while the natural geochemical and hydrological cycles operate over a time-scale that can stretch to hundreds of thousands of years The principal sources of radioactivity (over the long term) are indicated by the radionuclides listed at the center of each cycle Natural background levels of exposure to radiation are less than 300 mrem/year The total radiation exposure can be attributed to the nuclear fuel cycle

is less than 3 mrem/y (after R.C Ewing (2004) Environmental impact

of the nuclear fuel cycle In: Energy, Waste and the Environment: a Geochemical Perspective Geological Society Special Publication 236,

a worldwide concern This volume provides the basis for evaluating the environmental impact of this most recent nuclear tragedy

Rodney C Ewing Ann Arbor, Michigan

institute of technology (kit), Germany

Abstract: this chapter provides a short introduction and sets the scene

for this book on environmental radionuclide behaviour the focus is laid

on those radionuclides extracted from ores and/or produced in the course

of human activities related to energy production these can be of natural

or anthropogenic origin potentially released during mining and processing ores, during operation of nuclear power installations, reprocessing plants and nuclear waste repositories, and in case of accidents their manifold interactive reactions being typical to individual radionuclides and isotopes within various environmental compartments in geo-, eco- and biosphere are briefly described but will be the subject of more detailed descriptions and discussions in the individual chapters

Key words: fission products, actinides, environmental compartments, solubility, colloid formation, sorption, redox chemistry, radionuclide

migration, safety assessment

the present book focuses on those radiochemistry aspects which are relevant

in the context of nuclear energy application the further development of this technology has been put into question after the recent nuclear accident in Fukushima, Japan Quite often the argument comes up that our knowledge of the specific properties and the environmental behaviour of fission, activation products and actinides in natural systems is basically insufficient to allow

a sound assessment of risks connected with nuclear technologies Contrary

to the public perception, scientific knowledge in this field has developed greatly over the last decades Even though gaps are still visible, insight into the key processes and parameters controlling radionuclide migration and retention has very much improved this is because of both the increasing availability of various sensitive and powerful spectroscopic tools, due to the further development of theoretical approaches, and the increasingly available possibilities of carrying out specific field experiments under conditions close

to natural ones By this, the chemical speciation on a molecular level and the mobility under various environmental conditions of actinides and other

radionuclides can be identified and quantified The predictive capabilities of geochemical and migration modelling approaches could thus be substantiated

by such information

the idea of initiating the book in hand was the perception that after

40 to 50 years of research activities, a synopsis on current knowledge of chemical radionuclide behaviour in environmental systems should become available Facing an alarming trend of significantly decreasing nuclear research laboratories at universities and declining numbers of students in the field gives rise to apprehensions that existing knowledge could be lost and know-how transfer could become difficult The present book aims to provide

a state-of-the-art overview on the fundamentals of radionuclide bio/eco/geochemistry, specifying the most relevant processes and parameters relevant

to radionuclide mobility and their geochemical modelling Furthermore, it provides insight into the situation and processes at relevant contaminated sites such as Chernobyl and it describes the principles of remediation technologies

It also specifically focuses on performance assessment approaches related

to geological disposal it is clear that an overview cannot be exhaustive, but rather helps the reader to identify the most relevant processes to be considered and to provide the relevant literature for more detailed information the book is written by internationally recognized experts in these fields and will constitute a reference book for scientists and researchers addressing these interdisciplinary issues

We are convinced that such knowledge needs to be further developed and extended, independently of decisions made by several countries to not consider any more nuclear power as an appropriate option for future energy production one has to note that quite a number of countries still use nuclear energy and others are planning to extend existing or even initiate new nuclear power programmes Advanced reprocessing technologies are under development, allowing not only a more efficient utilization of uranium as an energy resource but also the partitioning of long-lived actinides for subsequent transmutation into stable or short-lived fission products The latter concept may allow reducing the long-term risks of high-level nuclear waste disposal but will not eliminate it As long as nuclear facilities for energy production

or waste treatment and disposal are in operation or at the planning stage, it

is apparent that comprehension of environmental radiochemistry issues is essential

ten naturally occurring so-called radioelements, radioactive elements with

no stable isotope, are presently known to exist in the earth’s crust these are mainly of primordial origin such as thorium (th), uranium (U) and radionuclides generated in their decay chain (e.g Ra, Rn, Po) in addition,

3Overview of radionuclide behaviour in the natural environment

about 60 radioactive nuclides of elements also having stable isotopes occur

which are continuously generated by the impact of cosmic radiation (e.g

than human-made radioactivity

in the present book the focus is, however, laid on those technologically relevant radionuclides related to the production of electricity by nuclear fission Different from the mostly dispersed and diluted natural radioactivity, man-made radioactive material generated for instance in nuclear power plants can reach very high specific activities and thus high radiotoxicities UO2 and in

worldwide Estimations predict until 2020 a cumulative spent fuel arising of

4 mass% fission products consisting mainly of isotopes of elements 34 (Se)

up to 64 (Gd) (see Fig 1.1) For fission reactors using thermal neutrons a bimodal fission mass yield distribution occurs with maxima at masses around

transuranic elements np, Pu, Am and Cm (and in very low trace amounts also Cf, Bk, Es and Fm) are generated by neutron capture reactions from U

Pu represents the main transuranic element fraction (ca 1%), while the other

so-called minor actinides amount to ~0.1 mass% in addition, radioisotopes are generated in claddings of fuel elements by neutron capture reactions

intermediate storage facilities, radioactive decay and heat production are primarily dominated by the fission products 137

of about 30 years After several hundred years they decay away still then the radiotoxicity of the waste is kept at a significantly higher level compared

to that of natural uranium for roughly 100.000 years this is predominantly due to the presence of the transuranic elements Pu and Am and their decay products toxic or highly radiotoxic properties can be attributed to most of the constituents of nuclear waste this is the reason for the internationally accepted concept of disposal of this type of waste temporarily in dedicated storage and ultimately in final repositories Usually, low and intermediate wastes are disposed in near-surface facilities, while high-level, heat-producing waste such as spent fuel or vitrified reprocessing waste is planned to be isolated from the biosphere in deep geological repositories

All these radionuclides can have a significant impact on human health and the natural environment if they are released accidentally from nuclear facilities in the case of nuclear power plant accidents, mainly the relatively short-lived fission products 131i, 137Cs and 90sr contribute to radiological doses to the local population as revealed by the consequences of the nuclear

Actinides Activation products

Fission products Fission and activation products

1.1 (a) Radionuclides contained

in spent nuclear UO2 fuel

Elements indicated with tinted backgrounds are constituents of spent nuclear fuel as radioelement

or radioisotope Nuclides may be generated by nuclear fission ( ), neutron activation reactions ( ) or as a consequence of neutron capture processes ( ) (b) Radiotoxicity contributions from various spent nuclear fuel constituents over time, relative to the radiotoxicity of the amount

of natural uranium required to produce 1 ton of nuclear UO2 fuel 2

5Overview of radionuclide behaviour in the natural environment

accidents of 1986 at Chernobyl and of 2011 at Fukushima In a final geological repository various barriers are set up in order to isolate and retain waste components and delay their transport for geological timescales only long-lived radionuclides and/or nuclides showing relatively high mobility under given geochemical conditions have to be considered as possibly environmentally relevant Among those are the potentially mobile long-lived fission and

actinides np, Pu and Am are usually considered rather immobile they have, however, a very complex chemistry and might be mobilized under certain environmental conditions, such as oxidizing environments, the presence

of colloidal transport or formation of anionic complexes Conclusions on their potential mobility and relevance can only be decided when all those aspects have been analysed A number of legacy sites and wastes from the early days of mainly military nuclear fission technologies contain different radionuclide mixtures in relatively complex chemical media Examples will

be discussed in various chapters of the book Significant amounts of waste radionuclides have already been released to the environment from, e.g., the Hanford site and Rocky Flats in the Us and from the Mayak complex in the former UssR those sites require now and in the future considerable efforts to ensure appropriate remediation measures

Properties of some relevant long-lived radionuclides originating from nuclear energy production are summarized in a rather generalized manner in table 1.1 More detailed information is given in the individual chapters

Relevant environmental compartments, in which radionuclide behaviour has

to be considered, depend on the location of the radionuclide source (Fig 1.2) if sources are at or close to the surface (atmospheric weapon tests, accidental releases from nuclear power or reprocessing plants and surface storage facilities), radionuclides are released to the atmosphere and indirectly (by precipitation) or directly (by effluents) into the soil or to the hydrosphere investigations on contaminated sites (see Chapters 15 and 16) show that

remain in upper soil zones and the rhizosphere and thus persist within the biological cycles for quite some time Bio- and ecochemical interactions, including microbiology, are thus of highest relevance for understanding the behaviour of radionuclides originating from those sources Relatively short-lived radionuclides may have direct impact on the radiological dose to the population due to external radiation or by their direct emission to biochemical cycles and thus to the food-chain in order to estimate radiological doses, all those processes must be implemented in radioecology models Chemical processes in the ecosphere are characterized by relatively rapid variations:

Table 1.1 Physical and chemical properties of some long-lived radionuclides in

nuclear waste originating from energy production by nuclear fission (for more comprehensive discussions, see the respective book chapters)

Radio-nuclide Physical properties Main relevant chemical

species

Possible immobilization reactions

Possible mobilization reactions

79 Se t1/2 = 360,000

years; b–

emitter

S 2– , Se(0), SeO 32–, SeO 42–

Sparingly soluble Se(0), Fe(Se,S)x form under reducing conditions

Under oxidizing and high pH conditions, mobile SeO 32– and SeO 42– can form

with solid NaCl

In general as Cl – very mobile

14 C t1/2 = 5700 year;

b– emitter CO3

2– , CH 4 , R–COOH Retention by CaCO 3 formation Very mobile if CHformed anaerobically4 is

Potentially mobile in Ca rich groundwaters

Usually very slightly mobile

99 Tc t1/2 = 213,000

years; b–

emitter

TcO 4–, TcO(OH) 2 , TcS 2

Sparingly soluble TcO(OH) 2 , TcS 2

form under reducing conditions

Under oxidizing conditions, mobile TcO 4–

forms; under reducing conditions colloid formation may increase solubility and mobility

Under oxidizing conditions NpO 2

is relatively mobile; relatively immobile under reducing conditions but colloid formation may increase solubility and mobility

238 U t1/2 =4.5 million

year;

a -emitter

UO 22+– carbonate/

hydroxo plexes; UO 2

com-(hydrated)

Sparingly soluble hydrated

UO 2 forms under reducing conditions

Under oxidizing conditions UO 2 forms stable complexes and

is moderately mobile; relatively immobile under reducing

7Overview of radionuclide behaviour in the natural environment

seasonal changes in temperature, precipitation and vegetation periods, relatively rapid surface water and near-surface groundwater movements influence chemical media and thus radionuclide behaviour Very often local chemical equilibria are not attained and reaction kinetics need to be considered, which

in many cases are not easily quantified (Fig 1.3) Such constraints represent

a challenge to a reliable modelling of those systems they also complicate a realistic assessment of the environmental impact of contaminated sites and the appropriate setup of remediation measures

conditions but colloid formation may increase solubility and mobility

239 Pu t1/2 = 24,000

years;

a -emitter

PuO 22+– carbonate/

hydroxo complexes;

PuO 2 , PuO 2

(hydrated);

Pu 3+ – carbonate/

hydroxo complexes

Under reducing conditions poorly soluble hydrated PuO 2

and sorbing Pu 3+

forms

Under oxidizing conditions PuO 2 / PuO 22+ and their aquatic complexes are relatively mobile; relatively immobile under reducing conditions but colloid formation may increase solubility and mobility

Table 1.1 Continued

Potential RN release from

– nuclear power plants,

– nuclear weapon tests,

– reprocessing plants,

– surface storage facilities,

– nuclear waste legacy sites

Potential RN release from

1.2 Environmental compartments to be considered for different

radionuclide release sources.

Radio-nuclide Physical properties Main relevant chemical

species

Possible immobilization reactions

Possible mobilization reactions

A main source of anthropogenic radionuclide release that has already taken place is atmospheric nuclear weapon tests During the 1950s and

of those nuclides emitted by nuclear accidents the radionuclide level in environmental compartments due to nuclear fallout is, however, rather low due to the strong dispersion

there is no strict boundary between the bio/ecosphere and the geosphere

By groundwater transport both compartments are interconnected A primary demand for a deep geological repository concept is thus the minimization of radionuclide transport on the long term from deep groundwater reservoirs

to shallow groundwater reservoirs or surface water some concepts rely on

a complete enclosure of the waste by the plastic host rock (repository in rock salt) or on a very slow, purely diffusive mass transport (repositories

in clay rock) other disposal concepts (e.g in crystalline rock) include elaborate technical and geotechnical barriers in order to keep groundwater separated from the waste in deep aquifer systems with slow transport and groundwater movement, there is a higher probability that chemical reactions such as complexation, precipitation and sorption attain at least some kind of local equilibrium (Fig 1.3) kinetic effects thus become less relevant but nevertheless important Biochemical processes are assumed to play a minor role in deep aquifers, even though microbial activities are still acknowledged

to be important, at least for, e.g., redox processes and the establishment of

a given geochemical medium

Radionuclide mobility and bioavailability in all compartments are determined by the coupled effects of three simultaneously occurring main processes schematically shown in Fig 1.4:

∑ the chemical speciation is governed by the given chemical parameters,

pH, Eh, ionic strength, presence of complexing ligands, etc it determines the overall radionuclide reactivity, mobility, bioavailability and toxicity solubility delimits the maximum quantity of radionuclides in the mobile aqueous phase Speciation can also be influenced by micro-organisms or biomolecules which are present in the environment speciation aspects are detailed in Chapters 2 to 6

∑ solid/water interface reactions contribute to radionuclide retention they can be of either a chemical or a physical nature with a broad variability

in binding strengths, depending on the individual radionuclide For polyvalent cations such as most actinide ions, sorption strongly hinders migration these processes are detailed in Chapter 8

∑ transport processes can be either the advective movement of water including solutes, or the diffusive transport of solutes driven by concentration gradients Furthermore, small-sized colloidal particles can also be transported in the aqueous phase All these processes obviously

9Overview of radionuclide behaviour in the natural environment

Characteristics vs

residence time

Surface waters watersDeep

Seconds Minutes Hours Days Months Years 100 000s yrs

Electron transfer reactions

Homogeneous/mono-electron transfer

Homogeneous/multiple-electrons transfer

Heterogeneous transfer (interfaces)

1.3 Characteristic time scales for different processes governing

the mobility of radionuclides in the environment compared to the average residence time of surface groundwater (surface waters) and deep groundwater (deep waters) (derived from reference 4) As long

as reaction times are shorter than residence times, establishment

of thermodynamic equilibria can be considered and kinetics can be neglected.

2 Solid/water interface retention

1 Aqueous

speciation

3 Transport processes (advection or diffusion)

Mineral surfaces

Rock porosity

1.4 Schematic representation of the three main processes occurring

in porous rock and governing radionuclide mobility in the

environment: aqueous speciation, retention and transport processes 5

play a significant role for the overall radionuclide migration and their relative contribution differs from one environment to the other transport processes are detailed in Chapters 7 and 10.

the presentation of the general chemical processes constitutes Part i of this book knowledge and data on those processes are of fundamental importance

to understanding radionuclide behaviour in all kinds of environmental compartments

Part ii concentrates on various aspects of radionuclide migration and their radioecological behaviour in specific environmental systems This includes fundamental insights into hydrology (Chapter 7), radionuclide interaction with mineral surfaces (Chapter 8) and colloidal matter (Chapter 10) An important

bridge between laboratory-derived data and nature is in-situ experiments (Chapter 12) and in-situ investigations of radionuclides in natural analogue sites

(Chapter 11) the latter studies help in understanding radionuclide behaviour under the very specific conditions of a given geochemical environment, but they also provide important systems for the validation of radioecological and geochemical modelling approaches in various spatial and time ranges A major challenge in the development of geochemical models is the coupling of geochemistry with hydrological transport A specific chapter is thus dedicated

to this issue, showing basic principles, limitations and application examples (Chapter 9) Finally, the chemical speciation of radionuclides in biological organisms is discussed in Chapter 13

After presenting the fundamentals of radioecological models (Chapter 14), Part III finally covers application issues: assessment of radionuclide behaviour in contaminated sites (Chapter 15), development of remediation concepts for contaminated sites (Chapter 16), and estimation of maximum radiological exposure of the population originating from final deep repositories and respective performance assessment considerations (Chapter 17)

1 k Fukuda et al., 2003, iAEA overview of Global spent Fuel storage,

iAEA-Cn-102/60.

2 k Gompper, A Geist, H Geckeis, 2010, Actinide separation from highly active

waste, Nachrichten aus der Chemie, 58, 1015–1019.

3 J Eikenberg, H Beer, S Bajo, 2004, Anthropogenic radionuclide emissions into the

environment, in Energy, Waste and the Environment: A Geochemical Perspective

(Eds R Gieré and P stille), Geological society of London.

4 J Bruno J., 1997, trace elemental modelling, in Modelling in Aquatic Chemistry

(Eds i Grenthe and i Puigdomenech), oECD nuclear Energy Agency, Paris, isBn 92-64-15569-4.

5 C Poinssot, Confinement and radionuclide migration in a deep geological repository, Habilitation Degree in Chemistry, University of Evry val d’Essonnes, France Published

as CEA report n° CEA-R-6177, issn 0429-3460, 85pp.

Abstract: The general objective of this chapter is to draw on basic

principles of aquatic chemistry and water–rock interaction that determine the composition of natural waters and therefore influence the behaviour

of aquatic species including radionuclides in the natural environment to a great extent The processes include precipitation and dissolution of minerals, sorption and ion exchange at mineral surfaces, co-precipitation, formation of aqueous complexes and redox reactions The complexity of such processes in natural aquatic environments can be very large and depends on the processes involved.

Key words: principles of water–rock interaction, dissolution and

precipitation, aqueous complexes, surface sorption, redox reactions.

compound ‘Pure’ water essentially is non-existent in the natural environment Natural water, whether in the atmosphere, in the ocean, lakes and rivers, or below ground, always contains dissolved minerals and gases as a result of its interaction with the atmosphere, lithosphere, and living organisms Chemical processes that affect the composition of natural waters include water–rock interactions, such as precipitation and dissolution of minerals and accordingly sorption of dissolved compounds and ion exchange at solid surfaces In addition, the dissolution of gaseous phases in water modifies the acidity/alkalinity of the waters The redox conditions of the water can be influenced by dissolution of minerals and gases as well as

by microbial activities leading to unstable conditions for certain solid phases Correspondingly, the speciation of dissolved compounds changes, e.g formation of specific aqueous complexes, which subsequently have

an important effect on the transport behaviour and on the reactivity of such elements The complexity of such processes can be very high and depends on the processes involved Heterogeneities within natural aquatic systems present a challenge to researchers developing models to predict

the behaviour and fluxes of environmental contaminants (Brantley et al.,

2.2.1 Physical and chemical properties

The particular role of water as a universal solvent and as an important transport medium on Earth depends strongly on its specific physical and

with hydrogen atoms at the tips and oxygen at the vertex The distance

of the covalent bonding between the H and the O atoms is 96 pm Since oxygen has a higher electronegativity than hydrogen, the side of the molecule with the oxygen atom has a partial negative charge The charge difference gives each water molecule a net dipole moment and cause water molecules

to be attracted to each other and to other polar molecules This attraction contributes to hydrogen bonding, and explains many of the properties of water

In this context, water has the second highest molar specific heat capacity

allow water to moderate Earth’s climate by buffering large fluctuations in temperature

The maximum density of water occurs at 3.98°C Water has the anomalous property of becoming less dense when it is cooled down to its solid form, ice

It expands to occupy 9% greater volume in this solid state, which accounts for the fact of ice floating on liquid water

The boiling point of water (and all other liquids) is dependent on the barometric pressure For example, on the top of mount everest water boils at 69°C, compared to 100°C at sea level Conversely, water deep in the ocean near geothermal vents can reach temperatures of over 100°C and remain liquid

In natural water almost all of the hydrogen atoms are of the isotope

not identical This is because the nucleus of deuterium is twice as heavy as

15Aquatic chemistry relevant to radionuclide behaviour

that of protium, and thus causes noticeable differences in bonding energies and hydrogen bonding

Water is a good solvent due to its polarity When an ionic or polar compound enters water it is surrounded by water molecules (hydration) The relatively small size of water molecules typically allows many water molecules

to surround one solute molecule The partially negative dipole ends of the water are attracted to positively charged components of the solute, and vice versa for the positive dipole ends In general, ionic and polar substances such

as acids, alcohols, and salts are relatively soluble in water, and non-polar substances such as fats and oils are not an example of an ionic solute is

being surrounded by water molecules The ions are then easily transported away from their crystalline lattice into solution with a solubility of 359 g/L

dipoles make hydrogen bonds with the polar regions of the sugar molecule (OH groups) and allow it to be carried away into solution with a solubility

of 2000 g/L at 25°C

Because many substances dissolve in water it is referred to as the universal solvent In nature water is rarely pure and some of its properties may vary slightly and notably from those of the pure substance

2.2.2 Main water components

Natural water environments are generally open systems and the chemical composition of natural waters results to a large degree from the reaction of mineral dissolution and precipitation They can be classified as saline water

in the oceans and freshwater occurring as groundwater, icecaps or glaciers, lakes, swamps and rivers Each of these natural waters has a specific salinity, resulting from the interaction of the numerous mineral assemblages and gas phases in contact with the aqueous phase Salinity, or total salt concentration,

is usually expressed in terms of total dissolved solids (TDS) in mg/L or as the electrical conductivity (EC) in mS/cm of the solution The major fractions

may enter in the composition of the aqueous solution alkali and alkali earth metals, transition metals, non-metals, and heavy metals are inorganic trace elements potentially found in the composition of the solution adjacent to a variety of organic trace compounds

of water isotopes in most hydrological processes: heavy isotopes occur preferentially in liquid (or solid) phases and the light isotopes in the gaseous phase This partitioning among the phases is the basis of most applications