Is Gas a Problem for Long-term Safety of a Repository in Boom Clay?

2009 ◽  
Author(s):  
E. Weetjens ◽  
X. Sillen
Keyword(s):  
Boom Clay

Methodology in Corrosion Testing of Container Materials for Radioactive Waste Disposal in a Geological Clay Repository

2001 ◽  
Author(s):  
Bruno Kursten ◽  
Frank Druyts ◽  
Pierre Van Iseghem
Keyword(s):  
Radioactive Waste ◽  
Corrosion Behaviour ◽  
Open Circuit ◽  
Geological Disposal ◽  
Boom Clay ◽  
Engineered Barriers ◽  
High Level ◽  
Aerobic And Anaerobic

Abstract The current worldwide trend for the final disposal of conditioned high-level, medium-level and long-lived alpha-bearing radioactive waste focuses on deep geological disposal. During the geological disposal, the isolation between the radioactive waste and the environment (biosphere) is realised by the multibarrier principle, which is based on the complementary nature of the various natural and engineered barriers. One of the main engineered barriers is the metallic container (overpack) that encloses the conditioned waste. In Belgium, the Boom Clay sediment is being studied as a potential host rock formation for the final disposal of conditioned high-level radioactive waste (HLW) and spent fuel. Since the mid 1980’s, SCK•CEN has developed an extensive research programme aimed at evaluating the suitability of a wide variety of metallic materials as candidate overpack material for the disposal of HLW. A multiple experimental approach is applied consisting of i) in situ corrosion experiments, ii) electrochemical experiments (cyclic potentiodynamic polarisation measurements and monitoring the evolution of ECORR as a function of time), and iii) immersion experiments. The in situ corrosion experiments were performed in the underground research facility, the High Activity Disposal Experimental Site, or HADES, located in the Boom clay layer at a depth of 225 metres below ground level. These experiments aimed at predicting the long-term corrosion behaviour of various candidate container materials. It was believed that this could be realised by investigating the medium-term interactions between the container materials and the host formation. These experiments resulted in a change of reasoning at the national authorities concerning the choice of over-pack material from the corrosion-allowance material carbon steel towards corrosion-resistant materials such as stainless steels. The main arguments being the severe pitting corrosion during the aerobic period and the large amount of hydrogen gas generated during the subsequent anaerobic period. The in situ corrosion experiments however, did not allow to unequivocally quantify the corrosion of the various investigated candidate overpack materials. The main shortcoming was that they did not allow to experimentally separate the aerobic and anaerobic phase. This resulted in the elaboration of a new laboratory programme. Electrochemical corrosion experiments were designed to investigate the effect of a wide variety of parameters on the localised corrosion behaviour of candidate overpack materials: temperature, SO42−, Cl−, S2O32−, oxygen content (aerobic - anaerobic),… Three characteristic potentials can be derived from the cyclic potentiodynamic polarisation (CPP) curves: i) the open circuit potential, OCP, ii) the critical potential for pit nucleation, ENP, and iii) the protection potential, EPP. Monitoring the open circuit potential as a function of time in clay slurries, representative for the underground environment, provides us with a more reliable value for the corrosion potential, ECORR, under disposal conditions. The long-term corrosion behaviour of the candidate overpack materials can be established by comparing the value of ECORR relative to ENP and EPP (determined from the CPP-curves). The immersion tests were developed to complement the in situ experiments. These experiments aimed at determining the corrosion rate and to identify the corrosion processes that can occur during the aerobic and anaerobic period of the geological disposal. Also, some experiments were elaborated to study the effect of graphite on the corrosion behaviour of the candidate overpack materials.

The Long-Term Dissolution Behaviour of the Pamela Borosilicate Glass SM527 - Application of SA/V as Accelerating Parameter

1991 ◽  
Vol 257 ◽  
Author(s):  
K. Lemmens ◽  
P. Van Iseghem
Keyword(s):  
Borosilicate Glass ◽  
Water Mixture ◽  
Boom Clay ◽  
Glass Dissolution ◽  
Dissolution Behaviour ◽  
Powdered Glass ◽  
Clay Slurry ◽  
Term Data ◽  
Solution Volume

ABSTRACTThe Al2O3 rich borosilicate glass SM527 was submitted to corrosion tests with glass surface area to solution volume ratios ranging from 10 to 10000 m-1. This latter condition would correspond with a 1000 fold acceleration relative to the reference MCCI condition. Powdered glass was used to reach SANV ratios of 500 m-1 and more. The leaching solutions were either distilled water or referred to Boom clay disposal conditions. The results based on the boron concentration in solution revealed a relatively linear dependence on SA/V.t0.5 in the pure solutions, on the longer term (DW and clay water). Diffusion is suggested to be the process governing the glass dissolution, although other processes should not be excluded. In a clay / clay water mixture (slurry), long term dissolution seems to be limited by saturation. Short term data for boron are largest in the clay slurry, but with time the boron concentrations converge to similar values in the three media considered. The use of SA/V as an accelerating factor is promising, but certainly requires additional research.

Static dissolution tests of α-doped UO2 under repository relevant conditions: Influence of Boom Clay and α-activity on fuel dissolution rates

2006 ◽  
Vol 932 ◽  
Author(s):  
Sonia Salah ◽  
Christelle Cachoir ◽  
Karel Lemmens ◽  
Norbert Maes
Keyword(s):  
Clay Fraction ◽  
Dissolution Kinetics ◽  
Spent Fuel ◽  
Dissolution Rates ◽  
Retention Capacity ◽  
Boom Clay ◽  
Dissolution Tests ◽  
Clay Formation ◽  
Α Activity

ABSTRACTSince reprocessing is no longer the reference policy in Belgium, studies on the direct disposal of spent fuel in a clay formation have gained increased interest in the last years. In order to determine to what extent the clay properties and the α-activity influence the dissolution kinetics of spent fuel for the long term disposal, static dissolution tests have been performed on 5 different types of α-doped UO2, representing a PWR fuel with a burn-up of 45 or 55 GWd · tHM−1 and fuel ages ranging between 150 and 90,000 years, in different Boom Clay (BC) media at room temperature and in an anoxic atmosphere for 90 to 720 days. The uranium activity in the clay fraction over time was found to be much higher than the U-activity in the leachates, which has been mainly ascribed to the high retention capacity of the BC. The average dissolution rate between 0 and 90 days obtained for the 5 types of α-doped UO2 were all found to be high and quite similar at ~263 µg · m−2 · d−1and a “longer-term” rate (181 to 720 days) ranging between zero and 15 µg · m−2· d−1. These results suggest that the activity of the fuels does not seem to have an effect on the UO2 dissolution rates under the considered test conditions. In order to study the partition/redistribution of U during UO2dissolution, sequential extraction experiments were performed. Results of the latter have provided a better mechanistic understanding of BC/spent fuel interaction processes as well as information on the role of the different minerals controlling the U-retention/immobilization.

The Second Safety Assessment and Feasibility Interim Report (SAFIR 2 Report) on HLW Disposal in Boom Clay: Overview of the Belgian Programme

2003 ◽  
Vol 807 ◽  
Author(s):  
Robert Gens ◽  
Philippe Lalieux ◽  
Peter De Preter ◽  
Ann Dierckx ◽  
Johan Bel ◽  
...  
Keyword(s):  
Safety Assessment ◽  
State Of The Art ◽  
Technical Feasibility ◽  
Geological Disposal ◽  
Boom Clay ◽  
Safety Case ◽  
Clay Formation ◽  
Main Barrier

ABSTRACTONDRAF/NIRAS – the Belgian radioactive waste management agency – has published in 2001 the SAFIR 2 report on request of the authorities. The SAFIR 2 report is to be considered as a state-of-the art report and not as a complete safety case. This report gives an overview of the Belgian R&D program related to the geological disposal of HLW and ILW for the period 1990–2000 in the Boom Clay (reference host rock). The three main outcomes of the SAFIR 2 report on which this paper will be more specifically focusing, are the following (including results reported after 2000): long-term safety functions, confirmation of the role of the Boom Clay formation as the main barrier and identification of practical difficulties with respect to technical feasibility (repository design).

Measurement of Glass Corrosion in Boom Clay Disposal Conditions

2001 ◽  
Author(s):  
Karel Lemmens ◽  
Marc Aertsens ◽  
Véra Pirlet ◽  
Hélène Serra ◽  
Elie Valcke ◽  
...  
Keyword(s):  
Dissolution Rate ◽  
Kinetic Modeling ◽  
Dissolution Time ◽  
Dissolution Test ◽  
Dissolution Rates ◽  
Boom Clay ◽  
Glass Dissolution ◽  
Dissolution Tests ◽  
Environmental Materials

Abstract To estimate the life-time of vitrified high level waste (HLW-glass) in geological disposal conditions in Boom Clay, the dissolution behaviour of waste glass has been studied in experiments in surface laboratories and in the HADES underground research facility of SCK•CEN since the 1980’s. The programme consists mainly of dissolution tests. The purpose of these tests is to understand the basic glass dissolution mechanisms, and to demonstrate realistic long-term dissolution rates. The main experimental variables are glass composition, environmental materials, temperature, and test duration. The studied glasses are the COGEMA glass R7T7, and the PAMELA glasses with SM539, SM527 and SM513 glass frit. The environmental materials comprise Boom Clay, metallic corrosion products and engineered barrier materials. Dissolution tests have been performed at temperatures from 40 to 190°C, for test durations from days to several years. The tests are performed with inactive glasses, which can be doped with radionuclides of interest. Because of the importance of silica sorption by the environmental materials, the dissolution test programme was extended with silica diffusion- and sorption tests in Boom Clay and FoCa clay. The interpretation of the experimental results is supported by geochemical and kinetic modeling. In the area of kinetic modeling, both analytical and Monte Carlo codes are applied. The dissolution tests have demonstrated that, although the presence of Boom Clay initially increases the glass dissolution rate, the long-term dissolution rate decreases for diluted clay / clay water slurries. This decrease has not yet been demonstrated for the R7T7 glass in compact Boom Clay, but is expected to occur here also on the long term. The dissolution rate decreases faster after sufficient addition of glass powder to the medium. This was tested in experiments with the R7T7 glass at relatively high clay concentration (2000 g of humid Boom Clay per liter clay water, this is about half the solid/liquid ratio of compact Boom Clay), at 40 and 90°C. Linear interpolation of the long-term mass losses resulted in dissolution rates of ∼ 0.01 g.m−2.day−1. The statistical uncertainties on the dissolution test results did not allow to demonstrate smaller rates. The minimum statistically significant dissolution rate depends on the test conditions. Therefore, the present SCK•CEN programme includes dissolution tests at long-term near-field conditions (this is at 30°C, with compact Boom Clay and FoCa clay), which are considered more representee for the long-term situation. In view of the uncertainties on the experimental long-term dissolution rates and on the long-term dissolution mechanisms, rates smaller than 0.01 g.m−2.day1 (about 1 μ/year) should not be used as best estimate in the present performance assessment studies for disposal in Boom Clay. A constant dissolution rate of 0.01 g.m−2.day−1 would correspond to a dissolution time for a R7T7 glass package of approximately 150 000 years. The minimum dissolution time is of the order of 104 years.

Osmosis: the key process that drives water uptake and swelling of Eurobitum Bituminized Radioactive Waste

MRS Advances ◽  
2016 ◽  
Vol 1 (62) ◽  
pp. 4109-4115
Author(s):  
K. Hendrix ◽  
N. Bleyen ◽  
S. Smets ◽  
W. Verwimp ◽  
X. Sillen ◽  
...  
Keyword(s):  
Water Activity ◽  
Water Uptake ◽  
Management Option ◽  
Boom Clay ◽  
Swelling Rate ◽  
Hygroscopic Salts ◽  
Clay Formation ◽  
Term Management ◽  
Pressure Evolution

ABSTRACTIn Belgium, the preferred long-term management option for Eurobitum bituminized ILW is its final disposal in a geologically stable clay formation such as the Boom Clay, which is studied as a reference host formation. After disposal, clay pore water will infiltrate the secondary concrete waste containers filled each with ten Eurobitum drums. Eurobitum contains hygroscopic salts, mostly NaNO3 (20-30 wt%) and CaSO4 (4-6 wt%), and thus will take up water and swell. If swelling is hindered, a pressure will be exerted on the concrete container and ultimately on the surrounding Boom Clay, possibly inducing stresses in the clay close to the disposal galleries. To improve our understanding of these processes, water uptake tests are ongoing in which inactive Eurobitum is contacted with 0.1 M KOH (representing young cement water). These tests suggest that the swelling is mainly driven by osmosis. This understanding was validated in the presented research by varying the water activity of the leachant in water uptake tests in both constant stress and constant volume conditions. After a stable swelling rate was reached in contact with 0.1 M KOH, the leachant was switched in the following order: nearly saturated (∼7.8 M) NaNO3 – 0.1 M KOH – nearly saturated NaNO3 – 4 M NaNO3 – 0.1 M KOH. The changes in swelling rate and pressure evolution correlated nicely to the changes in water activity. This confirms that osmosis is the key process governing the swelling of Eurobitum.

scholarly journals Drying-induced shrinkage of Boom clay: an experimental investigation

2016 ◽  
Vol 53 (3) ◽  
pp. 396-409 ◽  
Author(s):  
Noémie Prime ◽  
Séverine Levasseur ◽  
Laurent Miny ◽  
Robert Charlier ◽  
Angélique Léonard ◽  
...  
Keyword(s):  
Drying Shrinkage ◽  
Convective Drying ◽  
Boom Clay ◽  
Waste Storage ◽  
Geological Formation ◽  
Drying Conditions ◽  
High Level ◽  
Bedded Rock ◽  
Saline Solutions

Drying-induced shrinkage of geomaterials may have a strong effect on geostructure stability and deformation. The settlement of foundations and fracture openings in slopes, roads, and tunnel walls may be due to drying shrinkage. However, there is still a lack of knowledge concerning shrinkage evolution with time and shrinkage propagation within the material. In this study, the shrinkage of a specific clayey rock — Boom clay — under drying conditions is investigated experimentally. This rock is a deep geological formation, which is under study for high-level and long-term radioactive waste storage in Belgium. Two experimental campaigns are presented. The first, based on the vapour equilibrium drying technique and coupled with sample size manual measurement, aims to characterize the material shrinkage in balanced states. The second, based on the convective drying technique and coupled with shape monitoring using X-ray tomography, aims to analyse how shrinkage develops before reaching a steady state. Both approaches put in evidence the shrinkage anisotropy of this structurally bedded rock, with a ratio around 2 between the direction of maximum strains and the direction of minimum strains. However, the two drying techniques also provide complementary results as the relation between the amount of shrinkage and the retention curve (for uniform drying imposed with saline solutions) and the kinetics of shrinkage propagation inside the material (for nonuniform drying imposed with air convection).

In Situ Migration Experiments in the Boom Clay at Mol ; Experimental Method and Preliminary Results

1988 ◽  
Vol 127 ◽  
Author(s):  
M. Put ◽  
M. Monsecour ◽  
A. Fonteyne ◽  
H. Yoshida ◽  
P. De Regge
Keyword(s):  
Radioactive Waste ◽  
First Generation ◽  
Far Field ◽  
Radioactive Tracers ◽  
Experimental Conditions ◽  
Boom Clay ◽  
Long Term Experiments ◽  
Clay Formation

ABSTRACTA first generation of underground migration experiments is described, consisting of labelled clay cores emplaced in boreholes drilled in the Boom clay formation. The boreholes are sealed by natural convergence of the clay and porewater percolates through the labelled clay cores which are consolidated in situ. After monitoring of the radioactive tracers in the percolating porewater, the experiment is retrieved from the borehole and the tracer profile is measured in the clay cores. With the exception of accelerated porewater flow, due to the existence of a high hydraulic head around the underground gallery, the experimental conditions are close to those expected in the far-field of a closed repository for radioactive waste. The main advantage of this approach is the availability of real porewater during relatively long-term experiments. Results are reported for the experiments performed with europium and strontium tracers.

Functional Requirements and Performance Assessment: Application to the Case of Spent Fuel Disposal in Clay

2001 ◽  
Author(s):  
Jan Marivoet ◽  
Xavier Sillen ◽  
Peter De Preter
Keyword(s):  
Molecular Diffusion ◽  
Slow Release ◽  
Near Field ◽  
Functional Requirements ◽  
Spent Fuel ◽  
Systematic Analysis ◽  
Boom Clay ◽  
Safety Function ◽  
Clay Formation

Abstract Geological repository systems for the disposal of radioactive waste are based on a multi-barrier design. Individual barriers contribute in different ways to the overall long-term performance of the repository system, and furthermore, the contribution of each barrier can considerably change with time. In a systematic analysis of the functional requirements for achieving long-term safety a number of basic safety functions can be defined: physical confinement, retardation / slow release, dispersion / dilution and limited accessibility. In the case of the geological disposal of spent fuel in a clay formation a series of barriers are designed or chosen to contribute to the realisation of the basic safety functions. The physical confinement is realised by the watertight, high-integrity container, which prevents contact between groundwater and the confined radionuclides. In first instance the retardation / slow release function is realised by the slow dissolution of the waste matrix and by the limited solubility of many elements in the near field. However, the natural clay barrier provides the main contribution to this safety function. The migration of radionuclides through the Boom Clay is mainly due to molecular diffusion, which is an extremely slow process. Furthermore, many elements are strongly sorbed by the clay minerals what makes their migration even much slower. The dispersion / dilution function mainly occurs in the aquifer and the rivers draining the aquifer in the surroundings of the disposal system. Various performance indicators are used to quantify the contributions of each safety function and to explain the functioning of the repository system.

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