Development of guidance documents in the EURAD and PREDIS projects

Particular emphasis is dedicated to Knowledge Management activities within the EURAD (European Joint Programme on Radioactive Waste Management) and PREDIS (Pre-disposal management of radioactive waste) projects to ensure the capture of existing knowledge, transfer of knowledge between Members States and management of the knowledge for future generations. The EURAD project has three work packages dedicated to knowledge management. One of them, the EURAD Guidance work package (WP12) is developing a comprehensive suite of specific guidance documents that can be used by Members States with radioactive waste management (RWM) programmes that are at an early stage of development but can be beneficial also to more advanced programmes. The PREDIS project does not have a specifically allocated work package for guidance development. Rather, such activities are integrated within deliverables produced as part of the Strategic Implementation and State of Knowledge actions of the Roadmap contributions on predisposal waste management. The EURAD guidance work is based on the existing PLANDIS guide on RD&D planning, developed by the Implementing Geological Disposal of Radioactive Waste Technology Platform (IGD-TP). The guidance documents complement other documents prepared in parallel knowledge management activities inside EURAD project: the State of Knowledge documents. The differentiation is that guidance documents explain in more detail how the process can be established and performed, including illustrative examples. The guides are self-standing documents and integrated with the EURAD Roadmap. The target end users of the guidance are primarily programme owners and managers (i.e., governments/administrations, Waste Management Organisations, Research Entities and Technical Support Organisations) responsible for planning and implementing the RWM programme and the supporting RD&D activities at a national level, even though they might also be of use and interest to other interested stakeholders, such as representatives of civil society. To produce a first list of prioritised topics for guidance documents with the aim to select a topic for a pilot guide, the Guidance WP has developed a screening process that includes review by experts and end users. Based on the priority list, the first pilot guide was developed with the title “Cost Assessment and Financing Schemes of Radioactive Waste Management Programmes”. Experience gained during the selection of topics for the pilot guide and during its production are being incorporated into the procedure for identification of new topics for which guides will be developed. First, the degree of coverage of the EURAD Roadmap themes by suitable guide documents will be analysed by the WP 12 team. The analysis will be combined with feedback from experts verifying the needs for missing guides. Finally, the potential end user community representatives will be given the opportunity to comment on the prioritisation of selected guidance documents and make additional suggestions. The potential end users stay involved also during the production of the guides. This procedure aims to optimise the scarce expert resources in relation to the identified needs of guidance documents. This article explains the approach for selecting topics for guidance documents and the results obtained both in EURAD and PREDIS

Speciation and Transport of Radionuclides from the Chernobyl Accident within the Gide\ue5 Site

The transport and redistribution of radionuclides originating from the Chernobyl accident were studied within a 1 km2 area in the northeastern part of Sweden (the Gide\ue5 site). Physical and chemical speciation of the fallout radionuclides were investigated on water samples collected within the study site using techniques developed especially for this purpose. The concentration of cesium activity in the creek water had become established at a rather constant level of 0.1 Bq/L after 5 years. Of the cesium activity being transported by creek water, ~ 10% is transported as particulates and the rest as cations. The transport rate of the deposited radionuclides in the soil was studied over a period of 5 years. At the end of this period, the major portion of the deposited cesium activity was found in the upper 5 cm of the soil. The distribution of radionuclides in respect to the different soil grain size fractions was determined and the results showed a greater abundance of cesium activity in the silt-clay fractions. The ability of the soil to retard the deposited radionuclides was studied by sequential leaching. This leaching investigation showed that, on average, ~ 50% of 137Cs is tightly bound to the grains, except in of the A horizon, in which ~ 70% is strongly sorbed. The less tightly bound, i.e. mobile, part of the 137Cs activity makes up approximately 15%. Laboratory experiments were performed to investigate the sorption of the monovalent cations sodium, rubidium and cesium on soil collected within the Gide\ue5 site. Batch experiments on soil from different horizons showed a substantially greater retardation of cesium than of sodium and rubidium. The sorption of cesium was most significant in the A horizon (Kd value ~ 10 m3/kg). Sorption of sodium, rubidium and cesium on different grain size fractions showed a strong sorption on clay particles, even though a notable sorption was observed on soil particles larger than 1 mm. The sorption of cesium could not be coupled to the leaching of Na+, K+, Ca2+, Mg2+ and NH4+ from the soil particles. Column experiments were performed using undisturbed and partly unsaturated soil columns. The hydrodynamic properties in the soil columns were determined by using tritiated water added to the column as a pulse. The nuclides studied were 82Br-, 22Na+, 86Rb+ and 134Cs+. The results show that 82Br- can be used as a nonsorbing tracer. Of the cations studied, only sodium could be eluted from the soil column. A one-dimensional advection-dispersion model was applied to the break-through curves obtained for tritiated water and sodium. The Kd value obtained from the column experiment for sodium was similar to the Kd value obtained from batch experiments. The model applied was found to be applicable for weakly sorbing elements transported through an undisturbed and unsaturated soil column

Validation of isotopic analysis of depleted, natural and enriched uranium using high resolution ICP-OES

Analytical procedures for the reliable determination of uranium isotopes employing a commercially available high resolution (HR-)ICP-OES installed in a glove box were developed and validated. To this end, nine commonly used U emission lines were tested for their potential to provide a hyperfine splitting of the U signal, thus providing isotopic information. Among all emission lines tested, the wavelength region around 424.4 nm offered the largest spread between individual U signals, i.e. 233U, 235U, 236U, and 238U. This study focused specifically on the reliable determination of the abundances of 235U at 424.412 nm and 238U at 424.437 nm in samples containing depleted, natural and slightly enriched U, but also included specimens with rather high (up to ~90%) 235U enrichments. Appropriate selection of the spectral background and accurate positioning of the peaks proved essential for obtaining reproducible U isotope ratios. The accuracy of the developed methodology was confirmed by the analysis of eight certified isotopic reference materials as well as eight reference samples that have been characterised in an accredited laboratory in-house using TIMS. In addition, this study highlights the potential of the developed HR-ICP-OES procedure for identifying nuclear sources of various U specimens via the analysis of 233U (424.398 nm) and 236U (424.423 nm). In contrast to the commonly used techniques, the methodology applied in this study does neither require separation of U from the matrix prior to analysis nor the regular analysis of a reference sample with a known isotopic composition to correct for bias effects as it is the case for more sophisticated and precise mass spectrometric measurements. Nevertheless, HR-ICP-OES provides U isotopic information with reasonable accuracy and precision within a few minutes. As such, HR-ICP-OES can be employed as a reliable, fast screening tool to identify the U isotopic composition and as such, complements the more laborious TIMS analysis routinely employed for this purpose.JRC.E.5-Nuclear chemistr

Accurate isotopic analysis of uranium using high resolution ICP-OES

ICP-OES is considered a working horse for inorganic analysis in many analytical laboratories worldwide since decades. Besides the well established quantification of elemental concentrations in all major matrices, ICP-OES also provides the potential to determine the various isotopes of a single element such as Pb, Pu and U. Similar to a finger print, this approach of isotopic analysis that is not well recognised, delivers a characteristic isotope pattern which allows to trace the origin or the intended use of a specimen.JRC.E.5-Nuclear chemistr

Präzise Isotopenanalyse von Uran mittels hochaufgelöster ICP-OES

Die ICP-OES gilt seit Jahrzehnten als das Arbeitspferd für die anorganische Spurenanalyse in vielen analytischen Laboratorien weltweit. Neben der etablierten Quantifizierung von Elementkonzentrationen in allen gängigen Matrizes besteht jedoch auch die Möglichkeit, und dies ist viel weniger bekannt, mit der ICP-OES verschiedene Isotope ein und desselben Elementes (z. B. Pb, Pu, U) zu bestimmen. Diese Isotopenbestimmung liefert, ähnlich einem Fingerabdruck, ein charakteristisches Isotopenmuster, welches z. B. die Bestimmung der Herkunft oder des beabsichtigten Verwendungszwecks einer Probe erlaubt.JRC.E.5-Nuclear chemistr

Hydrogen Suppresses UO2 Corrosion

Release of long-lived radionuclides such as plutonium and caesium from spent nuclear fuel in deep geological repositories will depend mainly on the dissolution rate of the UO2 fuel matrix. This dissolution rate will, in turn, depend on the redox conditions at the fuel surface. Under oxidative conditions UO2 will be oxidised to the 1000 times more soluble UO2.67. This may occur in a repository as the reducing deep groundwater becomes locally oxidative at the fuel surface under the effect of aradiolysis, the process by which a-particles emitted from the fuel split water molecules. On the other hand, the groundwater corrodes canister iron generating large amounts of hydrogen. The role of molecular hydrogen as reductant in a deep bedrock repository is questioned. Here we show evidence of a surface-catalysed reaction, taking place in the H2¿UO2¿H2O system where molecular hydrogen is able to reduce oxidants originating from a-radiolysis. In our experiment the UO2 surface remained stoichiometric proving that the expected oxidation of UO2.00 to UO2.67 due to radiolytic oxidants was absent. As a consequence, the dissolution of UO2 stopped when equilibrium was reached between the solid phase and U4+ species in the aqueous phase. The steady-state concentration of uranium in solution was determined to be 9 1012 M, about 30 times lower than previously reported for reducing conditions. Our findings show that fuel dissolution is suppressed by H2. Consequently, radiotoxic nuclides in spent nuclear fuel will remain immobilised in the UO2 matrix. A mechanism for the surface- catalysed reaction between molecular hydrogen and radiolytic oxidants is proposed. 2009 Elsevier Ltd. All rights reserved.JRC.DG.E.5-Nuclear chemistr

High Burn-Up UO2 Fuel Corrosion under Reducing Conditions

A fission product and Pu rich porous structure forms at the radial periphery of LWR fuel pellet at a local burnup of ~70 GWd/tHM. This restructured fuel region, usually referred to as rim, will be the first part of the spent fuel to be exposed to groundwater in the event of failure of all the containment barriers. The corrosion behavior of rim-structured high burn-up UO2 fuel under conditions expected in a deep geologic repository is not fully understood today. To address this issue, a corrosion experiment on rim-containing fragments of high burnup UO2 fuel has been performed in a titanium autoclave. To simulate deep bedrock repository conditions, the autoclave was filled with a dilute carbonate groundwater, and pressurized to 4 MPa with H2. The results obtained during the first year of corrosion showed that the concentration of 238U in the leachate decreased below 5·10-10 M, the plutonium concentration fell below 6·10-12 M while the 137Cs concentration remained constant. Removal of the instant release fraction gave new insight of the chemical behavior of U, Pu and Cs under such conditions. Altogether, it was shown that the radiolytic oxidants produced by the intense a-, ß-, and ¿-radiation field of the high burn-up fuel were consumed in the system under study.JRC.DG.E.5-Nuclear chemistr

Corrosion of Irradiated MOX Fuel in Presence of Dissolved H2

The corrosion behaviour of irradiated MOX fuel (47 GWd/tHM) has been studied in an autoclave experiment simulating repository conditions. Fuel fragments were corroded at room temperature in a 10 mM NaCl/2 mM NaHCO3 solution in presence of dissolved H2 for 2100 days. The results show that dissolved H2 in concentration 1 mM and higher inhibits oxidation and dissolution of the fragments. Stable U and Pu concentrations were measured at 7 1010 and 5 1011 M, respectively. Caesium was only released during the first two years of the experiment. The results indicate that the UO2 matrix of a spent MOX fuel is the main contributor to the measured dissolution, while the corrosion of the high burn-up Pu-rich islands appears negligible.JRC.E.5-Nuclear chemistr

Spent Nuclear Fuel as Waste Material

In general this chapter deals with spent LWR fuel, mainly UO2 and mixed oxide fuel, in respect to its change of the chemical and mechanical properties during long-time storage in a deep underground repository. In more detail, the fuels alteration with time in respect to radionuclide inventory, temperature, radiation damage and structural stability is coupled to its corrosion, once it comes in contact with groundwater, in a final repository.JRC.E.5-Nuclear chemistr