Institute for Nuclear Waste Disposal (KIT Scientific Reports ; 7601)

108 Pages·2011·9.66 MB·English

by  Geckeis, H.

KIT ScIeNTIfIc RepoRTS 7600
Annual Report 2010
Institute for Nuclear Waste Disposal
Institut für Nukleare entsorgung
h. geckeis, T. Stumpf (eds.)
KaRlSRuheR INSTITuT füR TechNologIe (KIT)
ISSN 1869-9669

H. Geckeis, T. Stumpf (eds.)
Annual Report 2010
Institute for Nuclear Waste Disposal
Institut für Nukleare Entsorgung
Karlsruhe Institute of Technology
KIT SCIENTIFIC REPORTS 7600
Cover illustration (from left to right):
SEM image of a polished UO2 surface with studtite crystals, uranyl peroxide
hydrate, grown as secondary phase in water under γ-irradtiation (acquired
energy dose 1.5 MGy). Artificial view with pseudocolors.
SEM image of a spherical crystalline molybdate particle formed on the surface
of a simulated nuclear waste glass containing 5.5 wt% MoO .
3
Eu(III) fluorescence of calcite and clay containing sample after excitation at
394 nm.
Annual Report 2010
Institute for Nuclear Waste Disposal
Institut für Nukleare Entsorgung
H. Geckeis
T. Stumpf
(eds.)
Report-Nr. KIT-SR 7600
Impressum
Karlsruher Institut für Technologie (KIT)
KIT Scientific Publishing
Straße am Forum 2
D-76131 Karlsruhe
www.ksp.kit.edu
KIT – Universität des Landes Baden-Württemberg und nationales
Forschungszentrum in der Helmholtz-Gemeinschaft
Diese Veröffentlichung ist im Internet unter folgender Creative Commons-Lizenz
publiziert: http://creativecommons.org/licenses/by-nc-nd/3.0/de/
KIT Scientific Publishing 2011
Print on Demand
ISSN 1869-9669
Table of contents

1 Introduction to the Institut für Nukleare Entsorgung ............................................... 6
2 Highlights ..................................................................................................................... 8
3 Education and training .............................................................................................. 11
4 National and international cooperation ................................................................... 13
5 Fundamental studies: process understanding on a molecular scale ................... 16
5.1 Chemistry and thermodynamic of actinides in aqueous solution ........................ 16
5.2 Sorption on mineral surfaces .............................................................................. 22
5.3 Retention of radionuclides by secondary phase formation.................................. 28
6 Applied studies: radionuclide retention in the multi-barrier system .................... 33
6.1 Key processes influencing corrosion of highly active waste forms ..................... 33
6.2 Actinide retention in cemented nuclear waste forms .......................................... 39
6.3 Colloid impact on radionuclide migration ............................................................ 42
6.4 Numerical simulation studies .............................................................................. 47
7 Separation of long-lived minor actinides ................................................................ 53
8 Vitrification of high-level radioactive liquid waste.................................................. 58
9 Development of actinide speciation methods ......................................................... 66
9.1 R&D projects conducted at the INE-Beamline for Actinide Research
at ANKA and at external SR sources .................................................................. 66
9.2 Laser spectroscopy ............................................................................................. 71
9.3 Mass spectrometry methods ............................................................................... 74
9.4 XPS and TEM study of neptunyl (NpO +) - green rust interaction ....................... 78
2
9.5 NMR spectroscopy as a new tool for structural investigations on radioactive
materials in solution ........................................................................................... 80
9.6 Computational Chemistry ................................................................................... 83
10 Publications ............................................................................................................ 88

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1 Introduction to the Institut für Nukleare Entsorgung
R&D at the Institut für Nukleare Entsorgung, availability of thermodynamic data and a
INE, (Institute for Nuclear Waste Disposal) comprehensive understanding of these
deals with the long-term safety assessment for processes at a molecular scale.
final disposal of nuclear waste, the separation of
Relevant radionuclide concentrations in natural
minor actinides from high-level waste
groundwater lie in the nano-molar range, which
(partitioning) and the immobilization of high-level
is infinitesimally small in relation to the main
liquid waste by vitrification. All activities are
groundwater components. Quantification of
integrated into the programme Nuclear Safety
chemical reactions occurring in these systems
Research within the Energy Center of the
calls for the application and development of new
Karlsruhe Institute of Technology, KIT. INE
sophisticated methods and experimental
contributes to the German provident research for
approaches, which provide insight into the
the safety of nuclear waste disposal, which is in
chemical speciation of radionuclides at very low
the responsibility of the federal government.
concentrations. Innovative laser and X-ray
Based on the scheduled operation times for spectroscopic techniques are continuously
nuclear power plants in Germany, about 17.000 developed and applied. A theoretical group
tons of spent nuclear fuel will be generated. performs quantum chemical calculations on
About 6200 tons have been shipped to France actinide complexes as an additional tool to
and UK before 2005 for reprocessing to recover support experimental results.
plutonium and uranium. Therefore two types of
The long term safety assessment of a repository
high level, heat producing radioactive waste
for nuclear waste has to be demonstrated by
have to be disposed of safely, namely spent fuel
application of modelling tools on real natural
and vitrified high level waste from reprocessing.
systems over geological time scales. The
There is an international consensus that storage experimental research programme at INE aims
in deep geological formations is the safest way to acquire fundamental knowledge on model
to dispose of high level heat producing subsystems and to derive model parameters.
radioactive waste. It ensures the effective Geochemical models and thermodynamic
protection of the population and the biosphere databases are developed as a basis for the
against radiation exposure over very long description of radionuclide geochemical
periods of time. The isolation and immobilization behaviour in complex natural aquatic systems.
of nuclear waste in a repository is accomplished The prediction of radionuclide migration in the
by the appropriate combination of redundant geosphere necessitates a coupled modelling of
barriers (multi-barrier system). geochemistry and transport. Transferability and
applicability of model predictions are examined
INE research focuses on the geochemical
by designing dedicated laboratory experiments,
aspects of nuclear waste disposal. Special
field studies in underground laboratories and by
emphasis is given to actinides and long-lived
studying natural analogue systems. This
fission products because of their significant
strategy allows to identify and to analyse key
contribution to the radiotoxicity for long periods
uncertainties related to the accuracy and the
of time.
relevance of the developed models.
Relevant scenarios for the geological long-term
The Partitioning & Transmutation (P&T) strategy
behaviour of nuclear waste disposal have to
is pursued in many international research
take into account possible radionuclide transport
programmes. The objective is to reduce the time
via the groundwater pathway.
horizon for safe disposal of high level waste
Thermomechanical studies are performed at INE
from some hundred thousand to less than
in order to describe the evolution of the
thousand years by significant reduction of the
repository after closure. The possible
radiotoxicity and heat inventory. The aim of R&D
groundwater access to emplacement caverns is
at INE in P&T is to develop efficient processes
assumed to cause waste form corrosion.
for long-lived minor actinide separation from
Radionuclide mobility is then determined by the
high active nuclear waste for subsequent
various geochemical reactions in the complex
transmutation into short-lived or stable fission
aquatic systems: i.e. dissolution of the nuclear
products. INE develops highly selective
waste form (high-level waste glass, spent fuel),
extracting agents and performs experiments to
radiolysis phenomena, redox reactions,
derive kinetic and thermodynamic data for the
complexation with inorganic and organic ligands,
extraction reaction. R&D spans theoretical and
colloid formation, surface sorption reactions at
experimental work dedicated to a mechanistic
mineral surfaces, precipitation of pure solid
understanding of extraction ligand selectivity on
phases and solid solutions. Prediction and
a molecular scale, to development of extraction
quantification of all these processes require
processes.
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Within the third R&D topic at INE, the vitrification techniques are developed and applied for
of high level waste, INE contributes to the sensitive actinide and fission product speciation
decommissioning of nuclear facilities. The core such as time-resolved laser fluorescence
process technology for the Vitrification Plant spectroscopy (TRLFS), laser photoacoustic
(VEK) on the site of the former Karlsruhe spectroscopy (LPAS), sum frequency infrared
Reprocessing Plant (WAK) located at the KIT spectroscopy, laser-induced breakdown
Campus North has been developed by INE. detection (LIBD) and Raman spectroscopy.
Design of core process components, including Recently a tunable optical parametric oscillator
the glass melting furnace and the off-gas (OPO) laser system with TRLFS-detection was
cleaning system, comprises this development. installed for high resolution spectroscopy at
Moreover, INE was involved in functional testing liquid helium temperature. Speciation of
of major process systems, preparation of actinide-ion complexation and polymerization
qualification records and certification of product products in solution is facilitated by nano
quality, as well as in the performance of the cold electrospray time-of-flight mass-spectrometry
test operation. INE also played a leading role in (ESI TOF MS). Structural insight into actinide
hot operation of the VEK plant which started in species is obtained by extended X-ray fine
September 2009 and was completed in structure (EXAFS) spectroscopy at the INE-
November 2010. Beamline at the Karlsruhe synchrotron source
ANKA. The INE-Beamline, in the direct vicinity of
INE laboratories are equipped with the entire
INE hot laboratories and in combination with the
infrastructure necessary to perform
other analytic methods, represents a world-wide
radionuclide/actinide research, including hot
unique experimental and analytic infrastructure,
cells, alpha glove boxes, inert gas alpha glove
which both profits from and contributes to INE’s
boxes and radionuclide laboratories. State-of-
expertise in the field of chemistry and
the-art analytical devices and methods are
spectroscopy of the actinides. A new 400 MHz-
applied for analysis and speciation of
NMR spectrometer was installed and adapted to
radionuclides and radioactive materials.
measuring radioactive liquid samples. The first
α−, β−, γ−spectroscopy instruments exist for the
NMR-spectrum of an Pu(III)-complex was
sensitive detection and analysis of
measured in October 2010.
radionuclides. Trace element and isotope
analysis is made by instrumental analytical Quantum chemical calculations are performed
techniques such as X-ray fluorescence spectro- on INE’s computing cluster, which is equipped
metry (XRF), atomic absorption spectrometry with 17 nodes and 76 processors.
(AAS), ICP-atomic emission spectrometry (ICP-
Additional facilities at INE include a non-
AES) and ICP-mass spectrometry (Quadrupole-
radioactive vitrification test facility (1:1 mock-up
ICP-MS and high resolution ICP-MS). Surface
of the VEK plant) used to investigate and to
sensitive analysis and characterisation of solid
simulate vitrification processes for hot plants.
samples is done by X-ray diffraction (XRD),
The INE CAD workstations enable construction
scanning electron microscopy (SEM),
and planning of hardware components, process
photoelectron spectroscopy (XPS), atomic force
layout and flowsheets. The institute workshop is
microscopy (AFM) and laser-ablation coupled
equipped with modern machine tools to
with ICP-MS. INE scientists also have direct
manufacture components for specific
access to a TEM instrument at a nearby institute
experimental and analytical devices in hot
(Institute for Applied Science) on the KIT
laboratories.
Campus North site. Laser spectroscopic
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2 Highlights
Contributions collected in this report provide a hensive thermodynamic description. Experi-
representative overview of the scientific outcome mental studies were complemented by the final
of INE research activities in 2010. The structure report on the joint ReCosy Intercomparison
of the report follows widely the organisation of Exercise (EU FP project, coordinated by KIT-
the institute according to research topics: (1) INE), summarizing the present state-of-art in
basic research towards understanding redox determination methods in the context of
geochemical reactions of radionuclides on a nuclear waste disposal. (Chapter 5.1)
molecular scale and (2) applied studies on
Currently, there is a considerable lack of
radionuclide retention in multi-barrier system
knowledge with respect to the alteration of
under ‘real’ repository conditions. Both these
actinide bearing cement products in saline
topics are strongly linked together and cover a
solutions. Thus we studied the alteration of
broad range of chemical aspects for long term
hydrated ordinary portland cement (OPC) in
safety assessment of a repository for nuclear
chloride-rich brine using batch-type
waste. The third research topic (3) supports
experiments and by means of thermodynamic
these two areas by developing speciation
equilibrium calculations. The results of this study
methods and analytical techniques in order to
are important in particular for the safety
obtain detailed chemical information on
assessment of final disposal of low/intermediate
radionuclide speciation and structures. In
level active waste in rock salt. Since most
addition to spectroscopic methods, quantum
experiments were conducted with high cement
chemical calculations are increasingly
to brine ratios, reflecting disposal conditions,
implemented as an additional tool to gain insight
aqueous phase analyses were rather
into the molecular and electronic structure of
challenging. The calculated solution composition
radionuclide species. These experimental and
is in good agreement with the experimental
theoretical tools are applied to geochemical
results for a wide range of cement / brine ratios
studies and also to achieve mechanistic
(0.01 to 1.0 kg cement / L solution). Am(III)
understanding of solvent extraction processes
sorption in the cement / brine systems was
developed for separation of minor actinides from
quantified from experiments with equilibrated
fission lanthanides, which is indispensible for
solutions and cement corrosion products.
P&T.
Relatively high values of apparent sorption
Research dedicated to the immobilisation of
coefficients, R , for weakly alkaline (3000 < R <
high-level radioactive liquid waste is much more s s
6000 ml g-1) and highly alkaline conditions (R =
technically and application oriented. In this field, s
10000 ml g-1) demonstrate strong Am(III)
a vitrification plant on the WAK site using INE
retention by cement corrosion products (Chapter
technology was in hot operation from September
6.2).
2009 to November 2010. In parallel, the
Vitrification Project China (VPC) based on KIT- The focus of research within the international
INE’s technology was launched between Colloid Formation and Migration (CFM)
Chinese organizations and a German project is to understand formation of the
consortium. bentonite gel layer, erosion of bentonite
Important achievements of the research buffer/backfill material, generation of bentonite
activities in 2010 are listed below: colloids and their impact on radionuclide
In 2010, several research activities were transport in a shear zone under near-natural
focused upon the aquatic redox-chemistry of flow conditions. To overcome the high hydraulic
actinides and long-lived fission products. gradient towards the tunnel surface in the
The solubility and speciation of actinides depend underground laboratory, a sophisticated mega-
strongly on redox conditions and accordingly packer system counteracting the hydraulic
have to be analysed within this context to allow heads of the shear zone was constructed and
for quantitative predictions of solubility limits. installed at the end of 2009. Consecutively
Our work on Pu, Np and Tc has contributed to a performed colloid migration experiments in
better understanding of redox transformation 2010 under near-natural flow conditions with
processes and to constraining the stability fields increasing residence time demonstrate the
of dominant oxidation states. Studies on Pu and slow bentonite colloid RN sorption
Tc interaction with mineral surfaces yield new reversibility, especially for the tetravalent
insight into relevant mechanistic and kinetic elements. Furthermore, these experiments
processes under reducing conditions towards demonstrated the sensitivity of colloid transport
improved schemes for thermodynamic modeling. on flow path geometry/heterogeneity of the
Further studies on Pu and Np chemistry focus fracture/shear zone lending predictions based
upon oxidising conditions of penta- or hexa- on correlations such as e.g. colloid recovery
valent redox states, similarly aim at a compre-
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