Transfer of tritium in concrete coated with hydrophobic paints

An experimental study on tritium (T) transfer in porous concrete for the tertiary T safety containment is performed to investigate (i) how fast HTO penetrates through concrete walls, (ii) how well concrete walls contaminated with water-soluble T are decontaminated by a solution-in-water technique, and (iii) how well hydrophobic paint coating works as a protecting film against HTO migrating through concrete walls. The experiment is comparatively carried out using disks of cement paste which W(water)/C(cement) weight ratio is 0.6:1 with or without hydrophobic paints, and mortar disks which W/C/sand ratio is 0.6:1:2 with or without the paints. The hydrophobic paints tested in the present study are an epoxy polymer resin paint and an acrylic-silicon polymer resin one. After T exposure during specified time under a constant HTO vapor pressure in an acrylic box, the amount of water-soluble HTO on/in the disks is determined using a technique of H₂O dissolution during specified time. The results obtained here are summarized as follows: (1) HTO penetration in porous concrete can be correlated in terms of the effective diffusivity. (2) Its value in porous cement without coating is 1.2 × 10⁻¹¹ m²/s at 25 °C. (3) HTO penetrates only through pores in cement, and there is no path for HTO transfer in non-porous sand. (4) Rates of sorption and dissolution of HTO in disks of cement and mortar coated with the epoxy resin paint are correlated in terms of the effective diffusivity through the paint film which value is D_T = 1.0 × 10⁻¹⁶ m²/s. The rate-determining step is diffusion through the paint. (5) The epoxy resin paint works more effectively as an anti-HTO diffusion coating. (6) Another acrylic-silicon resin paint does not work well as anti-HTO diffusion coating. This may be because the hydrophobic property of the silicon resin paint is deteriorated with elongating the contact time with H₂O vapor or liquid. (7) The HTO uptake inside the epoxy paint is greater than that of the silicon one. (8) The permeation reduction factor (PRF) of HTO for the epoxy paint at steady-state is expected large, if HTO vapor only contributes to diffusion. However, when concrete surfaces coated with the epoxy paint are under wet conditions, the PRF value becomes smaller. All those results can be used to estimate the effect of HTO soaking in concrete walls in case of accidental T release in a fusion reactor room and to decontaminate wastes of tritiated concrete.     

EDF Waste Packages Transport and Compliance with Regulations: Prediction of Retention of Radionuclides by Cementitious Materials

Abstract

Different concrete waste packages have been designed by Electricite de France (EDF) for the long-term storage of radioactive Low Level Waste (LLW). Their main function is to confine radionuclides from the biosphere for three hundred years in a near-surface disposal. According to the transport regulation, a Type B package is needed for some waste like water filters. The water filters from EDF nuclear power plants are encapsulated in mortar and placed in a concrete container. Transport regulations for these containers have required the development of a methodology for safety assessment. The reference scenario of container degradation during transport considers a 9 m drop and a 800°C fire for 30 min. First, the different chemical and physical processes involved in the containment of radionuclides are analysed. In particular, the radionuclide transport mechanisms in cement-based materials have been reviewed. Secondly, the effects of a container drop on the mortar and concrete retention are discussed. Thirdly, in order to prove compliance with the regulations, a simplified model is proposed to predict the radionuclides release with time. It is concluded that cement-based materials offer high performance as a mechanical and chemical barrier to radionuclide releases for Type B packages.     

Sorption and Desorption of Radionuclides on the Structural Materials of a Nuclear Power System as Applied to Nuclear Power Plants with RBMK Reactors during Shutdown

The sorption and desorption of radionuclides on structural materials are studied as a function of the content of corrosion-activating ions, oxygen, hydrogen peroxide, and corrosion inhibitors in water. The strongest desorption is observed in aerated water containing chloride ions and the weakest desorption in a deaerated medium. The amount of desorbed radionuclides is correlated with the rate of corrosion of metals – it is highest on perlite steel (No. 20 steel) and lowest on zirconium alloys. Anode inhibitors prevent the corrosion of steel and transfer of radionuclides into the coolant.The sorption of radionuclides depends on the sample material. The highest sorption is observed on perlite steel and the lowest on zirconium alloy. Adding an inhibitor to the contaminating solution counteracts the effect of sorption, depending on the type of the structural material and radionuclide, and decreases it manyfold.     

Effects of Neutron-Irradiation on Tensile Properties of 3.5%Ni Steel

In an aerated soil layer under natural condition, water that infiltrates into it flows discontinuously because of repeated cycles of rainfall and drying. Therefore, column tests, in which 2,000 mi of deionized water was fed into sandy soil layer dried for 3~90 days after it is contaminated by ⁶⁰Co, ⁸⁵Sr and ¹³⁷Cs aqueous solution, were carried out to examine influence of the drying period on migration behavior of those nuclides.

All the radionuclides showed both a steeply decreasing part corresponding to their cationic form and a gradually decreasing part corresponding to their particulate form in the concentration distribution curve along the soil column depth. In the vicinity of the top surface of soil layer, no influence of drying on ⁶⁰Co and ¹³⁷Cs concentrations was observed, but ^S5Sr moved a little into a deeper part from the top surface with longer drying period. Such moving tendency of ^8ESr was found to be connected with the Ca²⁺ concentration in the interstitial water. In the deeper soil layer, no influence of drying on ⁸⁵Sr concentration was observed, but the ⁶⁰Co and ¹³⁷Cs concentrations were increased with the drying period. This is considered to be caused from that each product of the movable ⁶⁰Co(OH)₂ and the ¹³¹Cs adsorbed on the fine particle increased with the rise of pH and the fine particle concentration, respectively, during the drying period. Thus, this study has suggested possible causes affecting on the radionuclide migration under discontinuous flow condition.     

Effect of hydrophobic paints coating for tritium reduction in concrete materials

The effects of hydrophobic paint coating on a concrete material of cement paste on the tritium transport are investigated. The cement paste is coated with two kinds of paints, acrylic-silicon resin paint and epoxy resin paint. We investigated the amount of tritium trapped in the samples exposed to tritiated water vapor by means of sorption and release. It was found that both the hydrophobic paints could reduce effectively tritium permeation during 50 days exposure of tritiated water vapor. The effect of tritium reduction of the epoxy paint was higher than that of silicon while the amount of tritium trapped in the epoxy paint was larger than that of silicon due to difference of the structure. Based on an analysis of a diffusion model, the rate-determining step of tritium migration through cement paste coated with the paints is diffusion through the paints respectively. It was found that tritium was easy to penetrate through silicon because there were many pores or voids in the silicon comparatively. In the case of tritium released from the epoxy paint, it is considered that tritium diffusion in epoxy is slow due to retardation by isotope exchange reaction to water included in epoxy paint.     

氧化石墨烯材料对水溶液中放射性元素的吸附去除研究进展

作为一种高效的新型吸附材料，氧化石墨烯由于具有巨大的比表面积和丰富的含氧官能团等特性，在放射性元素的吸附去除中展现出巨大的应用潜力。本文主要介绍了氧化石墨烯及其复合材料的结构性质与制备方法，并对其在水溶液中吸附去除放射性元素铀、钍、铕的研究进行了综述，通过表面改性或与其它功能性材料复合可显著提高对放射性元素的吸附去除性能，并对吸附机理进行了总结，最后展望了今后的研究方向并提出了建议。     

Penetration of tritiated water vapor through hydrophobic paints for concrete materials

Behavior of tritium transfer through hydrophobic paints of epoxy and acrylic-silicon resin was investigated experimentally. The amounts of tritium permeating through their paint membranes were measured under the HTO concentration condition of 2–96 Bq/cm³. Most of tritium permeated through the paints as a molecular form of HTO at room temperature. The rate of tritium permeating through the acrylic-silicon paint was correlated in terms of a linear sorption/release model, and that through the epoxy paint was controlled by a diffusion model. Although effective diffusivity estimated by a diffusion model was obtained 1.1 × 10⁻¹³–1.8 × 10⁻¹³ m²/s for epoxy membranes at the temperature of 21–26 °C, its value was found to be hundreds times larger than that for cement-paste coated with epoxy paint. Hence, resistance of tritium diffusion through interface between cement-paste and the epoxy paint was considered to be the most effective in the overall tritium transfer process. Clarification of tritium transfer behavior at the interface is important to understand the mechanism of tritium transfer in concrete walls coated with various paints.     

部分建筑材料氡析出率测试分析

混凝土空心砌块、加气混凝土等新型建筑材料是目前房屋建筑通用的墙体建筑材料。本文通过实验测量了混凝土空心砌块、水泥砂浆、加气混凝土等建筑材料在相同的环境条件下氡析出的规律,测试了水泥砂浆覆面对建筑材料氡析出的影响,比较了部分建筑材料氡析出率的不同,为民用建筑防氡降氡设计和建筑材料的选用提供数据资料。     

Neutron radiography, a powerful method to determine time-dependent moisture distributions in concrete

Service life of reinforced concrete structures is often limited by penetration of water and compounds dissolved in water into concrete. Concrete can be damaged in this way and corrosion of steel reinforcement can be initiated. There is an urgent need to study water penetration into concrete in order to better understand deterioration mechanisms and to find appropriate ways to improve durability. Neutron radiography provides us with an advanced non-destructive technique with high spatial resolution and extraordinary sensitivity. In this contribution, neutron radiography was successfully applied to study the process of water absorption of two types of concrete with different water–cement ratios, namely 0.4 and 0.6. The influence cracks and of water repellent treatment on water absorption has been studied on mortar specimens. It is possible to visualize migration of water into concrete and other cement-based composites and to quantify the time-dependent moisture distributions as function of time with high spatial resolution by means of neutron radiography. Water penetration depth obtained from neutron radiography is in good agreement with corresponding values obtained from capillary suction tests. Surface impregnation of concrete with silane prevents capillary uptake of water. Even fine cracks are immediately filled with water as soon as the surface gets in contact. Results provide us with a solid basis for a better understanding of deteriorating processes in concrete and other cement-based materials.     

Chemo-mechanical coupling behaviour of leached concrete: Part I: Experimental results

This paper deals with concrete behaviour under chemical and mechanical degradations. Experimental investigations are described where the effects of the calcium leaching process of concrete on its mechanical properties are highlighted. The calcium leaching and mechanical tests on cement paste, mortar and concrete samples are presented. Because of the slow kinetics of leaching under deionised water, an accelerated method has been chosen by using an ammonium nitrate solution instead. The specimens are immersed into a 6 mol/l ammonium nitrate solution with a controlled pH disposal. To quantify the leaching evolution, the degradation depth is then measured at certain time intervals by means of a phenolphthalein solution. The experimental results show the chemical degradation of the cement-based material and the important role of aggregate in the calcium leaching process of concrete. Compression tests of concrete samples are also performed. We observe that there is a strong coupling between the calcium leaching and the mechanical behaviour; as leaching grows, a loss of stiffness and of strength are observed and a smoother post-peak behaviour is noted.     

Rice husk ash (RHA) as cement admixture for immobilization of liquid radioactive waste at different temperatures

Cementitious materials will initially act as a mechanical barrier preventing activated water flow through the waste for a long time, and thus will contribute to the retardation of dissolved radionuclides by the combination of physical and chemical interactions. Most chemical species in aqueous solutions will undergo some kind of (chemical) interactions with any solids of the cementations material. Therefore, it is of great importance to develop a quantitative understanding of the chemical processes involved and to strictly differentiate between physical and chemical aspects of radionuclide transport through such materials. A study is undertaken to determine the waste immobilization performance of (Cs⁺) wastes in cement-RHA mixtures. In addition to evaluating the effects of RHA on the leaching properties of cemented waste forms, the effect of addition of (RHA) on the strength of the cemented waste form is also investigated. However, RHA addition of 30% causes a significant increase in the hydraulic stability of cemented waste form. RHA enhances the strength; leaching and durability of cement may be through three primary actions which are the filler effect, the acceleration of ordinary Portland cement hydration and the pozzolanic reaction with calcium hydroxide (CH). The results were compared to control sample, and the viability of the RHA addition to concrete was verified. The use of these minerals results in ecological, economic and energy saving considerations.     

Numerical simulation of a high velocity impact on fiber reinforced materials

Whereas the calculation of a high velocity impact on isotropical materials can be done on a routine basis, the simulation of the impact and penetration process into nonisotropical materials such as reinforced concrete or fiber reinforced materials still is a research task.

We present the calculation of an impact of a metallic fragment on a modern protective wall structure. Such lightweight protective walls typically consist of two layers, a first outer layer made out of a material with high hardness and a backing layer. The materials for the backing layer are preferably fiber reinforced materials. Such types of walls offer a protection against fragments in a wide velocity range.

For our calculations we used a non-linear finite element Lagrange code with explicit time integration. To be able to simulate the high velocity penetration process with a continuous erosion of the impacting metallic fragment, we used our newly developed contact algorithm with eroding surfaces. This contact algorithm is vectorized to a high degree and especially robust as it was developed to work for a wide range of contact-impact problems. To model the behavior of the fiber reinforced material under the highly dynamic loads, we present a material model which initially was developed to calculate the crash behavior (automotive applications) of modern high strength fiber-matrix systems. The model can describe the failure and the postfailure behavior up to complete material crushing.

A detailed simulation shows the impact of a metallic fragment with a velocity of 750 m s⁻¹ on a protective wall with two layers, the deformation and erosion of fragment and wall material and the failure of the fiber reinforced material.     

The removal of the pertechnetate ion and actinides from radioactive waste streams at Hanford, Washington, USA and Sellafield, Cumbria, UK: the role of iron-sulfide-containing adsorbent materials

In previous work the adsorption of a number of radioactive ions from solution by a strongly-magnetic iron sulfide material has been studied. The material was produced by sulfate-reducing bacteria in a novel bioreactor. The uptake is rapid and the loading on the adsorbent is high due to the high surface area of the adsorbent and because many of the ions are chemisorbed. The structural properties have been examined using high-resolution imaging and electron diffraction, by transmission electron microscopy (TEM). The magnetisation versus field and temperature, extended X-ray absorption fine-structure (EXAFS) spectroscopy, X-ray absorption near edge structure (XANES) spectroscopy and neutron diffraction have been reported previously. The surface area is of the order of 400–500 m² g⁻¹, as determined by the adsorption of heavy metals, the magnetic properties, neutron scattering and transmission electron microscopy. Following the success of the biologically-generated material, Lidzey at Bio Separation Ltd. was able to produce an iron sulfide material with the tochilinite structure which has similar adsorption properties for cations, but not anions, as the biologically-generated material but the Lidzey material is considerably cheaper to produce. One of the radionuclides of particular interest is the pertechnetate ion TcO₄⁻. ⁹⁹Tc is a radionuclide determining the long-term environmental impact of the nuclear fuel cycle because of its long half-life and because it occurs normally in the form of the highly soluble pertechnetate ion which can enter the food chain. This paper examines methods by which adsorbent materials containing iron sulfide can play a part in the extraction and the safe long-term storage of many radionuclides and in particular the pertechnetate ion occuring at the Hanford Plant, Washington, USA and the Sellafield Plant, Cumbria, UK.     

Transfer pathways of 54Mn, 57Co, 85Sr, 103Ru and 134Cs in rice and radish plants directly contaminated at different growth stages

In order to study radionuclide transfer pathways related to direct contamination of plants, the above-ground parts of rice and radish plants were sprayed with a solution containing ⁵⁴Mn, ⁵⁷Co, ⁸⁵Sr, ¹⁰³Ru and ¹³⁴Cs in a greenhouse at 5 or 6 different times. Showing little difference among radionuclides, the interception factor increased as plants grew to maturity. Its highest observed value was 0.94 in rice and 0.83 in radish. Weathering losses of the intercepted activity by harvest were 32–89% in rice and 32–85% in radish depending on application time and radionuclide. Half lives for weathering loss were estimated to be longer on the whole for earlier applications. The translocation factor varied with application time by factors of 6–110 for hulled rice seeds and 2–23 for radish roots depending on the radionuclide. It varied with radionuclides by factors of 6–800 depending on application time and plant species. It was highest in the plants sprayed during active seed growth for rice and during early plant growth for radish. In general, ¹³⁴Cs and ⁵⁷Co had the highest translocation factors followed by ⁵⁴Mn, ⁸⁵Sr and ¹⁰³Ru. Based on the experimental results, radionuclide concentrations in the edible parts of mature plants were predicted for unit deposition.     

Experiment and Modeling for Solvent Leaching from Paint Matrix Considering Equilibrium

The leaching behavior of remaining solvent from an epoxy paint coating when it is submerged in water was experimentally studied. A leach kinetics model considering the equilibrium of the solvent concentration in the paint matrix and in water was developed. Three model parameters, equilibrium constant K, leaching rate k_d , and initial concentration of the solvent in the paint C⁰ _p, were evaluated based on the experimental results, and empirical correlation equations for them were obtained. The model showed good qualitative and quantitative agreement with the observed evolution of the leached solvent mass in the present experiment. Also, the model showed consistency with experimental data in a different configuration.     

Measurement of cross-sections for the (p, xn) reactions in natural molybdenum

Cross-sections for the residual radionuclide productions by proton-induced activation on natural molybdenum were measured up to 40 MeV by using a stacked-foil technique at the MC50 cyclotron of the Korea Institute of Radiological and Medical Sciences (KIRAMS). This work has given a new data set for the formation of the investigated radionuclides. The present results for most of the radionuclides showed in general good agreement with the earlier reported data as well as the theoretical data taken from the calculations based on the ALICE-IPPE code. The integral yields for thick targets were also deduced from the measured cross-sections of the produced radionuclides. The optimum production of the ^99mTc radionuclide with minimum impurities can be obtained at the energy ranges from 10 to 23 MeV, where the production yields were obtained as 597.15 MBqμA⁻¹h⁻¹ at saturation. The measured cross-sections are used for production of medically important radionuclides such as ^99mTc, ^94mTc and ^93m,gTc by using the medium-energy cyclotrons.     

Migration of Radionuclides (60Co, 85Sr and 137Cs) in Alkaline Solution (pH 12) through Sandy Soil Layer

Column experiments have been carried out on the migration of ⁶⁰Co, ⁸⁵Sr and ¹³⁷Cs in an alkaline solution (pH 12) through a sandy soil layer. Radionuclide--concentration distributions in both an effluent and a sandy soil layer were measured after pouring 200ml of aqueous solution containing the radionuclides on the layer, followed by eluting with 3,800 ml of distilled water.

Strontium-85 and ¹³⁷Cs gave a similar distribution pattern in the soil layer, while ⁶⁰Co migrated deeper into the layer. The migration velocity followed the order; ⁶⁰Co>⁸⁵Sr≧¹³⁷Ca. The order was different from that obtained with the radionuclides existed in a neutral solution. This suggested that the migration behavior of the radionuclides is significantly affected by the pH of the solution in which the radionuclides exist.

The sandy soil layer used here is considered as a linear system for the migration of in the solution of pH 12.     

Migration Behavior of Radionuclides (60Co, 85Sr and 137Cs) in Aerated Sandy Soil Layer

Differences of the migration behavior and desorption process for radionuclides (⁶⁰Co, ⁸⁵Sr and ¹³⁷Cs) in aerated sandy soil layer were studied by sprinkle of distilled water into the contaminated soil with above nuclides in column. Influence of difference desorption process on radionuclide migration was examined by changing the volume of distilled water sprinkled like rain on the contaminated soil.

Quantity of sprinkled water affected the concentration distribution of each radionuclide in soil layer. Each nuclide migrated deeper in the layer according to the increase of water amount, and especially, migration behavior of ⁸⁵Sr was remarkably influenced by water amount. It is observed that as to ⁸⁵Sr maximum contamination part in soil layer moved to deeper layer with increase of water amount, and that, as to ⁶⁰Co and ¹³⁷Cs, it moved almost never. On the other hand, activity concentration of ⁶⁰Co or ¹³⁷Cs in effluent was rather high (10^?6 μCi/ml) compared with that of ⁸⁵Sr, which could not be detected therein.     

Molecular Dynamics Simulations of the Interactions Between Tungsten Dust and Beryllium Plasma-Facing Material

In the present research,molecular dynamics simulation is applied to study the interactions between tungsten dusts and a beryllium plasma-facing material surface.Calculation results show that it is quite difficult for nanometer-size dust particles to damage the plasma-facing material surface,which is different from the micrometer-size ones.The reason may be the size difference between dust and crystal grains.The depth of dust penetration into plasma-facing materials is closely related to the incident velocity,and the impacting angle also plays an important role.Dust and material surface damage is also investigated.Results show that both incident velocity and angle can significantly influence the damage.     

Nuclear model calculations on the production of Sb via various nuclear reactions

Only very few radionuclides exist that decay exclusively by EC-mode without accompanying radiation, ¹¹⁹Sb is one of them. Auger emitter ¹¹⁹Sb (T_1/2 = 38.9 h, I_EC = 100%) is a potent nuclide for targeted radionuclide therapy based on theoretical dosimetry calculations at a subcellular scale. Auger electron emitting radionuclides in cancer therapy offer the opportunity to deliver a high radiation dose to the tumor cells with high radiotoxicity while minimizing toxicity to normal tissue.