Super Container Research Articles

High-Permeability Wood with Microwave Remodeling Structure

This paper presents the development of a microwave puffed wood (MPW) with novel and unique structural features in its internal structure that are based on natural wood (NW). The focus of the research was on the comprehensive visualization of the structural characteristics of MPW from the macroscopic to the microscopic scale followed by an exploration of its impregnation capabilities. The results showed that the volume of MPW increased by about 9% compared to NW due to the presence of a large number of cracked cavities. The CT images indicated that there was a significant difference between the macroscopic cracks produced by microwave processing and the natural cracks in the wood. The mercury intrusion test results showed that macro-pores increased while the micro-pores decreased in the MPW compared to in the NW. The MPW showed good fluid permeability and liquid absorption performance. The phenolic resin penetration rate of the MPW was about 20 times that of the NW, and the material absorption was more than 2 times that of the NW. The crack space enabled the MPW to serve as a fluid transportation and a storage warehouse. MPW is a super container based on natural materials. It has broad potential in more fields, such as in wood composite materials.

Анализ различных концепций захоронения РАО класса 1 в кристаллических породах

The paper considers most elaborated concepts for SNF and HLW disposal in crystalline rocks. It explores in detail an alternative concept suggesting the use of a super-container (SC) with a bentonite buffer located inside a steel body and the SC itself located in vertical wells inside a cement backfill, which is also used to seal fractures crossing the wells.

Effect of Thiosulfate on the SCC Behavior of Carbon Steel Welds Exposed to Concrete Pore Water Under Anoxic Conditions

The Supercontainer (SC) is the reference concept for the post-conditioning of vitrified high-level nuclear waste and spent fuel in Belgium. It comprises a prefabricated concrete buffer that completely surrounds a carbon steel overpack. Welding is being considered as a final closure technique of the carbon steel overpack in order to ensure its water tightness. Welding is known to induce residual stresses near the weld zone, which may lead to an increased susceptibility to stress corrosion cracking (SCC). In this study, slow strain rate tests were conducted to study the SCC behavior of plain and welded P355 QL2 grade carbon steel exposed to an artificial concrete pore water solution that is representative of the SC concrete buffer environment. The tests were performed at 140°C, a constant strain rate of 5 × 10-7 s-1 and at open circuit potential under anoxic conditions. The effect of thiosulfate on the SCC behavior was investigated up to levels of 600 mg/L S2O32-.

Carbon Steel Corrosion in Simulated Anoxic Concrete Pore Water for Nuclear Waste Disposal Application

Carbon steel is a potential canister material for high-level waste disposal in underground geologic repository systems where reducing conditions dominate after the thermal period. For example, the super container concept in the proposed Boom Clay repository concept in Belgium comprises a carbon steel overpack containing the waste and an outer stainless steel liner forming the boundary of an annular region containing a cementitious material. The outer surface of the carbon steel overpack would be in contact with concrete pore water with pH near 12.5, expected to persist for thousands of years. This study investigated carbon steel passivity, corrosion rate, repassivation, hydrogen generation, and hydrogen induced cracking tendency in simulated concrete pore water under anoxic conditions, and the effects of possible anions in the pore water such as Cl−, , and S2−. Carbon steel maintained its passivity at 50°C and 80°C up to a test period of 6 months and passive corrosion rates were mostly in the range of 0.1...

SCC susceptibility of carbon steel radioactive waste packages exposed to concrete porewater solutions under anoxic conditions

ABSTRACTThe supercontainer (SC) is the reference concept for the post-conditioning of vitrified high-level radioactive waste and spent fuel in Belgium. It comprises a prefabricated concrete buffer that completely surrounds a carbon steel overpack. Welding is being considered as a final closure technique of the carbon steel overpack in order to ensure its water tightness. Welding is known to induce residual stresses near the weld zone, which may lead to an increased susceptibility to stress corrosion cracking (SCC). In this study, slow strain rate tests were conducted to study the SCC behaviour of plain and welded P355 QL2 grade carbon steel exposed to an artificial concrete porewater solution. The tests were performed at 140°C, a constant strain rate of 5 × 10−7 s−1 and at open circuit potential under anoxic conditions. The effect of sulphide on the SCC behaviour was investigated up to levels of 15.6 mM S2− (500 mg L−1).This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

Electronic and spectral properties of ametal-organic super container molecule by single point DFT

ABSTRACTMetal-organic super container (MOSC) molecules are ideal candidates for photocatalysis due to their construction with transition metal centres and tuneable cavity sizes that could house catalytic sites. The basic electronic structure for a model of extremely large size (more than 2000 ions) is explored by single point calculation using unrestricted density functional theory, and Perdue–Burke–Ernzerhof functional in Vienna ab initio simulation package software. The information obtained through these calculations (such as density of states, absorbance spectra, and charge density) will allow for analysis of a MOSC's catalytic ability. Electronic characteristics of the nanostructures (MOSCs and their building blocks) in the ground and photoexcited electronic configurations are examined. We explore if the presence of transition metal ions with open shells in such close proximity to one another may result in high spin configurations and show any arrangement into ferromagnetic ordering. Spin-unrestricted computation was applied to evaluate how optical properties could be affected by d–d transitions. A scan of a spin-polarisation parameter allows one to resolve spin configuration and obtain a connection between theory and experiment. Analysis of Kohn–Sham orbitals of interest provides insight into charge transfer mechanisms, which were found to contribute to multiple low-energy charge transfer states to the electronic structure.

Detection and evaluation of cracks in the concrete buffer of the Belgian Nuclear Waste container using combined NDT techniques

The long term management of high-level and heat emitting radioactive waste is a worldwide concern, as it directly influences the environment and future generations. To address this issue, the Belgian Agency for Radioactive Waste and Enriched Fissile Materials (ONDRAF/NIRAS) has come up with a reference design for the geological disposal of this waste. In this design the wastes are first post-conditioned in a massive concrete structure called Supercontainer (SC) before being transported to an underground repository. The feasibility to construct this structure is being evaluated through a number of scaled models that are tested using various measurement techniques. This paper reports on the onset and evolution of the observed cracking of the concrete structure obtained by simultaneously applying Digital Image Correlation (DIC), Acoustic Emission (AE) and Ultrasonic Pulse Velocity (UPV) nondestructive testing techniques. In particular, the results highlight the time of onset and location of crack initiation as well as the width and depth of the cracks. Finally, emphasis is given to AE indices which indicate the severity of the cracks.

Preliminary results of corrosion monitoring studies of carbon steel overpack exposed to supercontainer concrete buffer

The supercontainer (SC) is the reference concept for the postconditioning of vitrified high level radioactive waste and spent fuel in Belgium. It is designed with a concrete buffer completely surrounding a carbon steel overpack. A half-scale (HST-2) experiment was set up to measure the instantaneous uniform corrosion rate, representative of the initial oxic phase, in situ. The test set-up has the same diameter as a full size SC, but it is limited in height to approximately half of a real SC. The corrosion rate of carbon steel is measured in four ways: weight loss measurements (carbon steel coupons), corrosion sensor based on linear polarisation resistance, corrosion sensor based on multisine electrochemical impedance spectroscopy and corrosion sensor based on single sine electrochemical impedance spectroscopy coupled to a unique analytical method. This paper presents the preliminary results of the corrosion rates measured with these independent methods.

Corrosion of Iron in Physically-Constrained Locations

A model has been developed to calculate the impact of the porous, outer layer of the passive film on the corrosion rate of the carbon steel overpack and on the structural integrity of the concrete in the annulus of the super container of the Belgian High Level Nuclear Waste (HLNW) disposal concept. Because the corrosion product occupies 2 – 6.5 times the volume of the iron from which it forms the development of the outer layer in the confined space between the carbon steel overpack and the concrete will result in the compression of the outer layer and a concomitant decrease in the porosity. If the porosity decreases to a sufficiently low value, the growth of the outer layer ceases and further corrosion is prevented. If the thickness of the corroded layer exceeds a critical value, the concrete will crack, because of the poor strength of cementations materials under tensile loading.

Electrochemical Impedance Modeling of the Passivity of Carbon Steel in Simulated Concrete Pore Water

The prediction of corrosion damage to times that are experimentally inaccessible by a large factor (e.g., to over 1000 years) is vitally important in assessing various concepts for the disposal of High Level Nuclear Waste. Such prediction can only be made using deterministic models, whose predictions are constrained to being “physically real” by the natural laws [conservation of mass, energy, charge and mass-charge equivalence (Faraday’s Law)]. In this paper, we describe the measurement of experimental data that will allow the deterministic prediction of damage to the carbon steel overpack of the super container in Belgium’s proposed Boom Clay repository by using the Point Defect Model to extrapolate damage to future times. We also describe an experimental program that is designed to generate values for various PDM parameters for the corrosion of carbon steel and stainless steel that will be required in making the damage predictions.

Surface Tests to Demonstrate the Construction Feasibility of the Belgian Supercontainer

The Supercontainer (SC) is a reference concept, adopted by the Belgian Agency for Radioactive Waste and Enriched Fissile Materials (ONDRAF/NIRAS), for the packaging of high level vitrified radioactive waste (HLW) and spent fuel (SF). The waste package consists of different components all designed to fulfil specific functions. One of these is a carbon steel overpack developed to prevent contact of the waste with the engineered barrier system and the host geological formation during the thermal phase. Another is a concrete buffer and cementitious filler, both developed to provide a high pH environment during at least the thermal phase, which ensures passivation of the overpack and provides radiological shielding during construction and handling of the SC. Finally, the presence of an outer steel envelope serves as a mould for the casting of the outer buffer while providing additional mechanical strength and confinement during transportation and handling of the waste package. As part of the first safety and feasibility case (SFC-1), ONDRAF/NIRAS has to demonstrate that no fundamental flaws exist regarding the feasibility to construct the SC. To this end, ONDRAF/NIRAS established a research programme consisting of desk studies, modelling, theoretical development and experimental testing. The primary objective of the experimental testing programme is to demonstrate the feasibility to construct the SC. This paper describes the test's setup and design and provides a summary of the main observations obtained during an experimental test performed to evaluate the construction feasibility of the SC.

Some important issues in electrochemistry of carbon steel in simulated concrete pore water Part 2 – Experimental

The prediction of corrosion damage to times that are experimentally inaccessible by a large factor (e.g. to over 1000 years) is vitally important in assessing various concepts for the disposal of high level nuclear waste. Such prediction can only be made using deterministic models, whose predictions are constrained to being ‘physically real’ by the natural laws [conservation of mass, energy, charge and mass charge equivalence (Faraday’s law)]. In this paper, the authors describe the measurement of experimental data that will allow the deterministic prediction of damage to the carbon steel overpack of the super container in Belgium’s proposed Boom Clay repository using the point defect model to extrapolate damage to future times. In this paper, the authors describe an experimental programme that is designed to generate values for various model parameters that will be required in making the damage predictions. The impact of chloride, sulphide and thiosulphate anions and mixtures of these species, on the electrochemical behaviour of carbon steel in contact with simulated concrete pore water, is examined.

The electrochemistry of carbon steel in simulated concrete pore water in boom clay repository environments

The prediction of corrosion damage of canisters to experimentally inaccessible times is vitally important in assessing various concepts for the disposal of High Level Nuclear Waste. Such prediction can only be made using deterministic models, whose predictions are constrained by the time-invariant natural laws. In this paper, we describe the measurement of experimental electrochemical data that will allow the prediction of damage to the carbon steel overpack of the super container in Belgium's proposed Boom Clay repository by using the Point Defect Model (PDM). PDM parameter values are obtained by optimizing the model on experimental, wide-band electrochemical impedance spectroscopy data. The super container concept for the disposal of high level nuclear waste (HLNW) in Belgium's proposed Boom Clay repository comprises a carbon steel overpack containing the waste and an outer, stainless steel liner that defines an annulus containing a cementitious material (similar to Portland cement-based concrete) (1). Both the outer surface of the overpack and the inner surface of the liner will be in contact with concrete pore water, which for our current purposes is defined as saturated Ca(OH) 2 + NaOH to yield a pH at 25 ◦ C of 13.5. It is recognized, however, that if (or when) the stainless steel liner is breached; dissolved sulfur species formed by oxidation of pyrite (FeS2) in the near field environment may penetrate into the annulus and cause accelerated corrosion of the carbon steel. Chloride ion is present in both the concrete and Boom clay environments, to an extent that it, too, must be considered a deleterious species that is capable of inducing passivity breakdown on both carbon steel and stainless steel if the potential is sufficiently high (2). Furthermore, during the initial period of waste disposal, depending upon the type of waste contained (reprocessed waste, non-reprocessed waste), the initial temperature will be in excess of 100 ◦ C and will decay over about 300 years to the ambient temperature of about 22 ◦ C. The calculations presented elsewhere (1) predict that oxygen in the annulus will be consumed quickly by corrosion and that the annulus environment will become essentially anoxic after a few years, after which water reduction, rather than oxygen reduction, becomes the principal cathodic reaction. As the oxygen concentration decreases, the hydrogen concentration increases, and the temperature decreases, the corrosion potential is predicted to increase, with the fall in temperature dominating at least over the first 300 years. Once the temperature has decayed to ambient and the annulus is saturated with hydrogen, the corrosion potential is predicted to be about −0.75 Vshe. In the present paper, we report the corrosion behavior of carbon steel during the initial oxic period, when the potential is expected to be between −0.4 V and +0.3 Vshe. We have been particularly concerned with measuring the steady state value of the passive current density and electrochemical impedance spectroscopy data for carbon steel in simulated concrete pore water (Ca (OH)2 + NaOH

Methodology to make a robust estimation of the carbon steel overpack lifetime with respect to the Belgian Supercontainer design

The Supercontainer (SC) design is the preferred Belgian option for the final disposal of vitrified high-level waste (VHLW) and spent fuel (SF) in deep underground clay layers. The SC consists of a carbon steel overpack, containing VHLW canisters or SF assemblies, surrounded by a thick concrete buffer, which in turn, is entirely encased in a stainless steel envelope. An integrated R&D strategy is developed to demonstrate and defend that the integrity of the carbon steel overpack can be ensured at least during the thermal phase. This integrated approach, proposed to estimate the lifetime of the carbon steel overpack, consists of three steps: lifetime prediction, validation, and confidence building. Under the predicted conditions within the SC (highly alkaline concrete buffer), the carbon steel overpack is expected to undergo uniform corrosion (passive dissolution). The methodology exists in demonstrating that corrosion forms other than uniform corrosion (e.g. localised corrosion such as pitting corrosion, crevice corrosion and stress corrosion cracking) cannot occur (‘exclusion principle’). This paper elaborates on how this methodology is implemented.