Waste In Belgium Research Articles

Heating pulse tests under constant volume on Boom clay

Boom clay formation is a potential natural host rock for geological disposal of high-level nuclear waste in Belgium. Heating pulse tests with controlled power supply (maximum temperature was limited to 85 °C) and controlled hydraulic boundary conditions were performed under nearly constant volume conditions to study the impact of thermal loading on the clay formation. Selected test results of intact borehole samples retrieved in horizontal direction are presented and discussed. The study focuses on the time evolution of temperature and pore water pressure changes along heating and cooling paths, i.e. pore pressure build-up during quasi-undrained heating and later dissipation at constant temperature.

The effect of high pH alkaline solutions on the mineral stability of the Boom Clay – Batch experiments at 60°C

Boom Clay is currently viewed as a reference host formation for studies on deep geological disposal of radioactive waste in Belgium. The interactions between bulk rock Boom Clay and 0.1 M KOH, 0.1 M NaOH, 0.1 M Ca(OH)2, young cement water and evolved cement water solutions, ranging in pH from 12.5 to 13.2, were examined as static batch experiments at 60 °C to simulate alkaline plume perturbations, which are expected to occur in the repository due to the presence of concrete. Both liquids and solids were investigated at specific times between 90 and 510 days in order to control the elemental budget and to search for potential mineralogical alterations. Also, the clay fraction was separated from the whole-rock Boom Clay at the end of each run and characterized for its mineralogical composition. Thereby, the importance of the mineral matrix to buffer the alkaline attack and the role of organic matter to protect clay minerals were also addressed. The results indicate that the degree of geochemical perturbation in Boom Clay is dependent on the initial pH of the applied solution together with the nature of the major cation in the reactant fluids. The higher the initial pH of the media, the stronger its interaction with Boom Clay. No major non-clay mineralogical alteration of the Boom Clay was detected, but dissolution of kaolinite, smectite and illite occurred within the studied experimental conditions. The dissolution of clays is accompanied by the decrease in the layer charge, followed by a decrease in the cation-exchange capacity. The highest TOC values coincide with the highest total elemental concentrations in the leachates, and correspondingly, the highest dissolution degree. However, no quantitative link could be established between the degree of organic matter decomposition and clay dissolution.

Investigating the time-dependent behaviour of Boom clay under thermomechanical loading

Boom clay, a stiff clay, has been selected as a potential host formation for the geological disposal of radioactive waste in Belgium. The underground research facility HADES has been constructed to enable various in situ experiments to be performed on Boom clay so as to study the feasibility of high-level radioactive waste disposal, and to provide reliable data on the performance of Boom clay as a host formation. Among the various laboratory studies performed on samples extracted from the HADES facility to investigate the thermo-hydro-mechanical behaviour of Boom clay, relatively few were devoted to the time-dependent behaviour, limiting any relevant analysis of the long-term behaviour of the disposal facility. The present work aims at investigating the time-dependent behaviour of Boom clay under both thermal and mechanical loading. High-pressure triaxial tests at controlled temperatures were carried out for this purpose. The tests started with constant-rate thermal and/or mechanical consolidation and ended with isobar heating and/or iso-thermal compression at a constant stress rate or by step loading. The results obtained confirmed the effect of the overconsolidation ratio (OCR) on the thermal volume changes (i.e. thermal dilation under high OCRs and thermal contraction with OCR close to unity). Significant effects of temperature as well as of compression and heating rates were also observed on the volume change behaviour. After being loaded to a stress lower than the preconsolidation pressure (5 MPa) at a low temperature of 25°C and at a rate lower than 0·2 kPa/min, the sample volume changes seemed to be quite small, suggesting a full dissipation of pore water pressure. By contrast, after being subjected to high loading and heating rates (including step loading or step heating), the volume changes appeared to be significant, particularly in the case of stresses much higher than the preconsolidation pressure. Because of its low permeability, full consolidation of Boom clay required a long period of time, and it was difficult to distinguish consolidation and creep from the total volume change with time.

Solutions for the long term management of radioactive waste in Belgium

Solutions for the long term management of radioactive waste in Belgium

Development of the Supercontainer Design for Deep Geological Disposal of High-Level Heat Emitting Radioactive Waste in Belgium

ABSTRACTONDRAF-NIRAS has recently selected a Supercontainer with a Portland Cement (PC) buffer as the preferred new reference design for disposal of HLW and spent fuel. The selection process involved a multi-criteria analysis of alternative design options, which were evaluated against a range of long-term safety and feasibility criteria. A PC concrete has been chosen for the buffer because this will provide a highly alkaline chemical environment, which will last for thousands of years. In this environment the external surface of the overpack will be passivated and overpack corrosion will be inhibited. The concrete buffer also has low-hydraulic conductivity to slow the infiltration of external fluids to the overpack surface, and provides radiological shielding.ONDRAF-NIRAS has made a preliminary evaluation of the viability of the reference Supercontainer design. The following areas were reviewed and investigated: radiolysis, thermo-hydraulic (TH) behaviour of the concrete buffer, metal corrosion, the chemical and mineralogical evolution of the concrete buffer, and relevant industrial experience. This paper describes the main findings, and identifies remaining design and performance uncertainties. Prioritisation and recommendations for future work are also given.

A Review of Corrosion Considerations of Container Materials Relevant to Underground Disposal of High-Level Radioactive Waste in Belgium

ABSTRACTThe underground formation that is currently being considered in Belgium for the permanent disposal of high-level radioactive waste and spent fuel is a 30-million-year-old argillaceous sediment (Boom Clay layer). This layer is located in the northeast of Belgium and extending under the Mol-Dessel nuclear site at a depth between 180 and 280 meter.Within the concept for geological disposal (multibarrier system), the metallic container is the primary engineered barrier. Its main goal is to contain the radioactive waste and to prevent the groundwater from coming into contact with the wasteform by acting as a tight barrier. The corrosion resistance of container materials is an important aspect in ensuring the tightness of the metallic container and therefore plays an important role in the safe disposal of HLW. The metallic container has to provide a high integrity, i.e. no through-the-wall corrosion should occur, at least for the duration of the thermal phase (500 years for vitrified HLW and 2000 years for spent fuel).An extensive corrosion evaluation programme, sponsored by the national authorities and the European Commission, was started in Belgium in the mid 1980's. The main objective was to evaluate the long-term corrosion performance of a broad range of candidate container materials. In addition, the influence of several parameters, such as temperature, oxygen content, groundwater composition (chloride, sulphate and thiosulphate), γ-radiation, … were investigated. The experimental approach consisted of in situ experiments (performed in the underground research facility, HADES), electrochemical experiments, immersion experiments and large scale demonstration tests (OPHELIE, PRACLAY). Degradation modes considered included general corrosion, localised corrosion (pitting) and stress corrosion cracking.This paper gives an overview of the more relevant experimental results, gathered over the past 25 years, of the Belgian programme in the field of container corrosion.

Neptunium Speciation in Humic Acid-rich Clay Water upon Interaction With Radioactive Waste Glass Samples

ABSTRACTOrganic complexes of actinides are known to occur upon interaction of high level waste glass and Boom Clay which is a potential host rock formation for disposal of high level waste in Belgium. The solubility and mobility of237Np, one of the most critical radionuclides, can be affected by the high dissolved organic carbon content of the Boom Clay porewater through complexation with the humic substances. The influence of humic substances on the Np behaviour is considered through dissolution tests of Np-doped glasses in Boom Clay water and through fundamental study of the specific interaction between Np(IV) and the humic acids using spectroscopic techniques. High Np(IV) concentrations are found in the glass dissolution tests. These concentrations are higher than what we should expect from the solubility of Np(OH)4, the solubility limiting solid phase predicted under the reducing conditions and pH prevailing in Boom Clay. Studying the specific interaction of Np(IV) with humic acids in Boom Clay porewater, high soluble Np concentrations are also measured and two main tetravalent Np-humate species are observed by UV-Vis spectroscopy. The two species are interpreted in terms of mixed hydroxo-humate complexes, Np(OH)xHA with x = 3 or 4. These species are the most likely species that can form according to the pH working conditions. Using thermodynamic simplified approaches, high complexation constants, i.e. log β131and log β141respectively equal to 46 and 51.6, are calculated for these species under the Boom Clay conditions.Comparing the spectroscopic results of the dissolution tests with the study of the interaction of Np(IV) with humic substances, we can conclude that the complexation of Np(IV) with the humic acids may occur and increases the solubility of Np(OH)4upon interaction of a Np-doped glass and the Boom Clay porewater.

Transport of Radioactive Waste in Belgium

AbstractThe transport of radioactive waste in Belgium is organised by NIRAS/ONDRAF, which is the national agency for the management of radioactive waste and enriched fissile materials. The paper gives an overview of the main categories of radioactive waste and the packagings used for the shipment of these wastes. It also gives a short description of the transport systems that were designed for the shipment of standard packages for radioactive waste with a surface dose rate up to 300 mSv.h−1.