LiNO3 Effect on Corrosion Prevention of Aluminum with Complex Shapes

The LiNO₃ effect on aluminum corrosion prevention after land disposal of cement-solidified dry active wastes was examined quantitatively, in the event that the LiH (AlO₂)₂·5H₂O (Li-Al) preservation film was not formed on aluminum surfaces during the solidification process. It is especially probable for these bare surfaces to be left when the wastes include components of complex shapes. LiNO₃ dissolves from the waste forms into underground water to form the Li-Al preservation film. So, we thought that the LiNO₃ addition would prevent the corrosion. We measured the volume of hydrogen gas generation in mortar-soaked water during the Li-Al preservation film formation, as functions of LiNO₃ addition amount, the weight ratio of water to mortar when the mortar-soaked water was produced, and the aluminum surface area, to quantify the effect.

We found that aluminum corrosion was inversely proportional to the LiNO₃ addition. For the corrosion to be less than 10^?5m in 10³h, the initially added amount of LiNO₃ must be 1.5wt% of the sum of cement and sand. Regardless of the weight ratio of water to mortar when the mortar-soaked water was produced, hydrogen gas generation with LiNO₃ was 10% as much as that without it, in 5 x 10³h. Because of the Li-Al preservation film formation reaction, hydrogen gas generation was proportional to the cubic root of the aluminum surface area.     

LiNO3 Addition to Prevent Hydrogen Gas Generation from Cement-Solidified Aluminum Wastes

LiNO₃ addition to the cement solidified miscellaneous wastes has been proposed for preventing hydrogen ges generation caused by the corrosion of aluminum materials contained in the wastes. To determine an additive among alkaline metal ions, galvanic current was measured in 0.1 M alkaline metal hydroxide solution between aluminum and platinum electrodes. The volume of hydrogen gas generated from an aluminum specimen was measured in a KOH solution with LiNO₃, LiCl, LiBr, Li₂CO₃ or Li₂SO₄ to decide the best additive. Applicability of the chosen additive to cement was confirmed by hydrogen gas generation measurement from an aluminum specimen in cement paste. The prevention mechanism was analyzed by X-ray diffraction, SEM and SIMS.

The current measured in LiOH solution decreased with time, then reached 0 μA/mm², while the current was detected in other alkaline metal hydroxide solutions. The least volume of hydrogen gas generation was measured in a KOH solution with LiNO₃. The volume of generated hydrogen gas in cement paste with LiNO₃ was less than 10% of that without LiNO₃. The results of analyses showed that an insoluble film of LiH(AlO₂)₂5H₂O was formed on the aluminum surface.

These results suggested that LiNO₃ addition to cement is effective to prevent hydrogn gas generation by formation of the insoluble film on aluminum.     

Extraction of Lithium from Sea Water with Metallic Aluminum

Extraction of lithium from sea water was investigated. It was found that a corrosion product of metallic aluminum immersed in sea water extracts lithium from it selectively. Effects of the temperature and the pH of sea water, and of the initial concentration of lithium in it were examined. On the basis of the analysis of the surface deposit on aluminum, which is a corrosion product of aluminum, the selectivity coefficients were calculated. For the extraction of lithium from natural sea water, the values of K ^Li _Na ^Li _MgK ^Li _Ca and ^Li _K were 9.9 × 10², 1.1×10, 4.5×10 and 4.4 × 10², respectively.     

Lithium nitrate as a fusion reactor coolant fluid?: A thermochemical assessment

In connection with possible application as a coolant fluid in fusion reactors, molten LiNO₃ and LiNO₃/LiNO₂ mixtures, and their mixtures with Na/K nitrates, have been evaluated with respect to their high temperature stability, their ability to reversibly dissolve and release tritium and, in a very limited sense, their corrosiveness toward structural alloys. The results of the primarily thermochemical evaluation indicate that with respect to thermal/radiolytic decomposition and corrosivity LiNO₃/LiNO₂ may be suitable for application up to R 700^°K; however, with respect to reversibility/irreversibility of tritium release, it appears unsuitable at all likely operating temperatures (R 675–800°K).     

Effect of pH on corrosion behavior of CuCrZr in solution without and with NaCl

CuCrZr is a high copper alloy widely used as electrical and thermal conducting material, especially in heat exchangers in nuclear reactors. In this respect, the physical and fatigue properties of CuCrZr have been extensively studied. The electrochemical behavior of CuCrZr, on the other hand, has not been adequately investigated. In the present study, the effect of pH on the corrosion behavior of CuCrZr in aqueous solutions without and with chloride (0.6 M NaCl) was studied. The pH of the solutions is found to exert significant influence on the corrosion behavior of CuCrZr. In acidic solutions without chloride, the corrosion of CuCrZr is ascribed to active dissolution with soluble products. In neutral and alkaline solutions without NaCl, the presence of oxides on the surface of CuCrZr leads to a noble shift in corrosion potential and passivation results in increased corrosion resistance. In chloride solutions at various pH values, the chloride ions influence the formation of the surface layers and the anodic dissolution process during polarization. At high pH, CuCrZr shows significant passivity and high corrosion resistance due to the growth of Cu₂O/Cu(OH) film which hinders further dissolution whereas at low pH the corrosion resistance is lowered due to active dissolution of Cu.     

Inconel690在ETA/NH_3水化学环境中的均匀腐蚀行为研究

本文在模拟压水堆二回路的高温高压水化学环境下,研究了蒸汽发生器传热管材料镍基合金Inconel690试样在乙醇胺(ETA)和氨(NH3)水化学环境中的均匀腐蚀行为。结果显示:在5 000h均匀腐蚀试验后,ETA水化学环境下试样的均匀腐蚀速率为0.21mg/(m2·h),NH3水化学环境下试样的均匀腐蚀速率为0.50mg/(m2·h);在ETA水化学环境下试样表面形成的氧化膜中铬含量更高,氧化膜的保护性更好。以上结果表明,Inconel690在ETA水化学环境下的耐蚀性强于NH3水化学环境。     

A simulation of radiolysis of chloride solutions containing ferrous ion

ABSTRACT

To investigate the effect of dissolved species from steels on the radiolysis processes of Cl^?, radiolysis simulations of solutions containing both Cl^? and Fe²⁺ were carried out. The results showed that the generation of radiolytic products (H₂O₂, O₂ and H₂) increased mainly by the addition of Fe²⁺, and the concentrations of H₂O₂ and O₂ increased with increasing dose rate. Moreover, radiolysis of Fe²⁺ solutions also induced noticeable pH drop due to the hydrolysis of Fe³⁺. This pH drop enhanced the reactivity of Cl^? with ^?OH, which induced additional generation of H₂O₂ and O₂. These results show that low concentrations of Cl^? (1 × 10^?3 mol/dm³ = 35 mg/kg) in the presence of Fe²⁺ could influence the generation of H₂O₂ and O₂ during water radiolysis. On the other hand, it is considered that these effects of Fe²⁺ and Cl^? on water radiolysis are less important for corrosion of steels due to the low concentrations of H₂O₂ and O₂ generated if the concentrations of these additives and dose rate are sufficiently low. The other process, such as dissolution of iron enhanced by FeOOH, might predominantly induce corrosion under the conditions of solutions with low concentrations of H₂O₂ and O₂.     

Characterization of Cement Alteration Process by Transmission Electron Microscopy with High Spatial Resolution

Application tests for advanced TEM analysis techniques were carried out to study the cement alteration processes associated with water penetration at high spatial resolution. Prior to TEM analysis, we measured the changes in the penetration coefficient and determined the characteristics of the penetrating water in order to gain a fuller understanding of the overall process. These experiments revealed that the process begins with the preferential dissolution of Ca(OH)₂. After most of the Ca(OH)₂ is dissolved out, the penetration coefficient increases, while the pH value of the water decreases. It has been demonstrated that scanning transmission electron microscope (STEM) techniques are quite useful for determining local structures and compositions in the cement at sub-micron meter spatial resolution. The preferential dissolution of Ca ions results in refinement of cement grains. When the Ca/Si ratio decreases to 1.05, most grains have a round shape in the sub-micron range. X-ray mapping suggests the formation of 3CaO·A1₂O₃· xSiO₂·(6-2x)H₂O (x=0-3). Ettringite has been mostly dissolved out. But Mg ions remain still in form of brucite. When Ca/Si reaches 0.91, the morphology has changed to a mixture of fibers and granules. The fibers have been identified as a mixture of Calcium Silicate Hydrate Gel and silica gel. Quantitative EDX composition analyses have demonstrated that the granules are altered products of hydrogrossular, 3CaO·A1₂O₃·2SiO₂·2H₂O, which have been predicted by previous theoretical studies. It is also been shown that hydrotalcite with Mg and Al has been also formed. The results thus obtained are in principle in accordance with the process predicted by previously proposed thermodynamic models.     

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.     

核级不锈钢焊接接头钝化膜耐蚀性能和半导体特性研究

采用电化学阻抗谱(EIS)、场发射扫描电子显微镜(SEM)、Auger扫描能谱仪(AES)以及容抗测试技术(M-S曲线),研究了316LN/316L不锈钢焊接接头在模拟压水堆一回路高温高压水中形成的钝化膜的耐蚀性能和半导体特性。结果表明,焊缝区、热影响区和母材区形成的钝化膜的耐蚀性能不同,热影响区钝化膜开路电位及电化学阻抗等均低于其他区域,说明热影响区钝化膜的耐蚀性能最差,这主要与钝化膜的致密程度、厚度及Cr氧化物的含量有关。M-S曲线表明,母材区钝化膜平带电位为-0.7V,较其他区域(-0.4V)负移,表明有BO-3等阴离子在钝化膜表面吸附,加之具有较低的施主和受主浓度,可排斥侵蚀离子的腐蚀,使之较其他区域有更强的耐蚀性能。     

Dissolution Phenomena of Ca0-Si02-H20 Gel at Ca/Si>l Coexisting with Ettringite System

We have studied the influence of interaction between Ca0-Si02-H2 0 (C-S-H) gel and ettringite (AFt) on their dissolution regarding the initial chemical feature of degraded cement pore water. In this work, firstly dissolution experiments were performed in C-S-H gel at Ca/Si=1.0, 1.2 and 1.47 coexisting with AFt of which amount was 5% of mol corresponding to each C-S-H gel. Secondly, assuming the congruent dissolution of AFt, dissolution of the same system was calculated by combining with the dissolution model of C-S-H gel at 1< Ca/Si ≤1.5, considering without interaction between C-S-H gel and AFt. Measured and calculated results of Ca, Si, Al and S total concentrations and pH values of C-S-H gel coexisting with AFt system were investigated. Discrepancies between experimental and calculated Ca, Si, Al and S total concentrations and pH values suggested the importance of interaction phenomena in C-S-H gel coexisting with AFt system. By considering the substitutions of Al(OH)^? ₄ and SO^3? ₄ with Si tetrahedra in the structure of C-S-H gel, these discrepancies are discussed in this study.     

The general corrosion behavior of ENiCrFe-7 weld overlay cladding material in deoxygenated high-temperature and high-pressure water

The general corrosion behavior of Alloy ENiCrFe-7 in deoxygenated high-temperature and high-pressure water was investigated. The results showed that the precipitates of Alloy ENiCrFe-7 included niobium carbide and Al-Ti-O compounds, and the weight gain increased fast firstly before 2250 h, then the weight gain slowed down. There were obvious large particles spread on denser oxide film after 3000 h exposure. Ni was present at a single chemical metallic Ni state, Feⁿ⁺ content of the outer layer was close to 60%, which was much higher than that of the matrix. The oxide film consisted of an inner layer and an outer layer, the inner layer was mainly composed of Cr₂O₃ and the outer layer was mainly composed of Fe₃O₄ and FeCr₂O₄. Finally, it is found that the preferential corrosion location of pitting was niobium carbide precipitates by in same site observation, while Al-Ti-O compounds was not dissolved in deoxygenated high-temperature and high-pressure water for 1500 h exposure. The size and number of the pitting was not significantly changed with increasing exposure time.     

Free Energy of Formation for Solid Lithium Nitride

Breakthrough properties of Cs were examined at 298 K using columns packed with K⁺ forms of ferrierites. Breakthrough curves showed symmetrical S-shaped profiles at lower space velocity (SV) below 50/h. The adsorption zone of Cs increased linearly with flow rate and exceeded the length of packed column over 50/h. The S-shaped curves were obtained at lower HN0₃ concentrations below 1 mol/dm³, whereas Cs readily flowed out through the column in the presence of 5 mol/dm³ HNO₃. The break point was shifted to lower bed volumes with increasing concentration of coexisting cations; the amounts of Cs adsorbed were lowered in the presence of competing cations in the order, Na⁺>K⁺>Rb⁺. Cesium adsorbed on ferrierites could be quantitatively eluted with 1 mol/dm³ KNO₃ as an eluent. The selective removal of Cs was achieved by passing the simulated radioactive liquid wastes through the ferrierite columns.     

Microstructural Characterization of SCC Crack Tip and Oxide Film for SUS 316 Stainless Steel in Simulated PWR Primary Water at 320°C

Recent studies on stress corrosion cracking (SCC) behaviors of austenitic stainless steels in hydrogenated high-temperature water show that low potential SCC (LPSCC) can occur on cold-worked SUS 316 stainless steel (hereinafter, 316SS). In this study, oxide films and crack tips on cold-worked 316SS exposed to hydrogenated high-temperature water were characterized using analytical transmission electron microscopy (ATEM), grazing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES) in order to study the corrosion and SCC behaviors of these films and crack tips. A double layer structure was identified for the oxide film after a constant extension rate tensile (CERT) test. The outer layer was composed of large particles (0.2–3 μm) of Fe₃O₄ and the inner layer consisted mainly of fine particles (~10 nm) of FeCr₂O₄. In addition, nickel enrichment was identified at the metal/oxide interface. Particles of Fe₃O₄ were also identified on the crack walls. These results indicate that the same electrochemical reactions had occurred inside and outside the crack. The crack tip area was filled with corrosion products of a chromium-rich oxide. In addition, nickel enrichment was observed at the crack tip. The formation of the nickel-enriched phase indicates that a selective dissolution reaction of iron and chromium occurred at the front of the LPSCC crack.     

Oxidation and vitrification of aluminum with lead borate glass for low level radioactive waste treatment

ABSTRACT

For the direct vitirification of low level radioactive wastes containing metallic aluminum, the oxidation and vitirification of aluminum was carried out using lead borate glass as a flux. Among the six fluxes employed in this study, 0.11Na₂O ?3PbO ?B₂O₃ was the most suitable for the oxidation and vitirification of aluminum based on the initial oxidation rate and alumina solubility. The increase of the lead fraction in the flux increased the oxidation rate, while the sodium fraction affected the alumina solubility resulting in the product maintaining its transparent appearance. The agglomerate product by the oxidation was confirmed metallic lead by X-ray diffraction analysis, and its impurities, aluminum, boron and sodium, were lower than 0.2 wt% by the quantitative analysis.     

Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (III)

The stress corrosion cracking (SCC) of structural materials used in boiling water reactors has been studied at relatively low hydrogen peroxide (H₂O₂) concentrations, around lOppb, which was assumed to be representative of the corrosion environment formed in hydrogen water chemistry (HWC). The 1/4T compact tension specimen was used for measurement of crack growth rates (CGRs) of sensitized type 304 stainless steel in high temperature and high purity water. Crack length was monitored by a reversing direct current potential drop method. Since H2O2 is easily decomposed thermally, a polytetrafluoroethylene-lined autoclave was used to minimize its decomposition on the autoclave surface. The CGR in the H₂O₂ environment differed from that in the O₂ environment even though the electrochemical corrosion potential (ECP) for both conditions was the same. The data implied that the ECP could not be used as a common environmental deterministic parameter for SCC behavior at higher potentials for different oxidant conditions. The corrosion current density was found to play an important role as an environmental index for SCC, which was given as just the current density at the ECP at a specific oxidant concentration. The CGRs were found to be written as CGR = (3.8±0.6)xl0^-3 _icor +(l-5±1.6) x 10^-8mm/s using the calculated corrosion current density i_corbelow 10^-4 A-cm^-2.     

Electrolytic dissolution characteristics of SIMFUEL in carbonate solutions of high concentration

This work studied anodic dissolution characteristics of a SIMFUEL electrode at several potentials in carbonate solutions of a high concentration at several pHs. The electrolytic uranium dissolution of SIMFUEL was much affected by a corrosion product of UO₂CO₃ generated at the electrode during the dissolution in carbonate solution. The corrosion product distorted the voltammogram of SIMFUEL in the potential region of oxygen evolution and increased the overpotential of oxygen evolution at the electrode. The effective dissolution of the SIMFUEL electrode in a carbonate solution could be obtained at an applied potential such as +4 V (vs SSE) or more which had an overpotential of oxygen evolution high enough to rupture the corrosion product on the electrode surface. The corrosion potential of SIMFUEL decreased with pH in the carbonate solution, and the dissolution rate and current efficiency of the SIMFUEL increased with a decrease of pH in the carbonate solution.     

Online measurement of the atmosphere around geopolymers under gamma irradiation

ABSTRACT

The gas production of wasteforms is a major safety concern for encapsulating active nuclear wastes. For geopolymers and cements, the H₂ produced by radiolytic processes is a key factor because of the large amount of water present in their porous structure. Herein, the gas composition evolution around geopolymers was monitored online under ⁶⁰Co gamma irradiation. The transient evolution of the hydrogen release yield was measured for samples with different formulations. Its evolution and the final values are consistent with the presence of a pseudo-first-order chemical reaction consuming hydrogen in the samples. The results show that this phenomenon can significantly reduce the hydrogen source term of geopolymer wasteform provided their diffusion coefficient remains low. Lower hydrogen production rates and faster kinetics were observed with geopolymer formulations in which pore water pH was higher. Besides hydrogen release, a steady oxygen consumption was observed for all geopolymer samples. The oxygen consumption rates are proportional to the diffusion coefficients estimated in the modelization of hydrogen recombination by a pseudo-first-order reaction.     

Protective Oxide Film on Alloy X750 Formed in Air at 973 K

An effective pre-oxidation method for Alloy X750 was developed to reduce general corrosion in an oxygenated aqueous environment such as in BWR core water. The optimum condition of preoxidation in air at elevated temperatures was found to be 5–20 h at 973 K by considering the allowance condition of heat treatment for age-hardening.

Some characteristics of the corroded oxide film have been clarified by surface analyses with XMA, SIMS, AES, XPS etc. The film was composed of double oxide layers, namely a highly crystallized NiFe₂O₄ outer layer and a high Cr₂O₃ content inner layer. The passive property of the film has been recognized to be due to the nature of the oxides whereby NiFe₂O₄ restricts the dissolution of metals because of its low solubility and Cr₂O₃ restricts the diffusion of metal ions because of its high binding energy and low diffusion coefficient.     

The corrosion of spent UO2 fuel in synthetic groundwater

Leaching of high burnup BWR fuel for up to 3 years showed that both U and Pu attain saturation rapidly at pH 8.1, giving values of 1–2 mg/l and 1 μg/l respectively. The leaching rate for Sr-90 decreased from about 10⁻⁵/d to 10⁻⁷/d but was always higher than the rates for U, Pu, Cm, Ce, Eu and Ru. Congruent dissolution was only attained at pH values of about 4. When reducing conditions were inposed on the pH 8.1 groundwater by means of H₂/Ar in the presence of a Pd catalyst, significantly lower leach rates were attained.The hypothesis that alpha radiolytic decomposition of water is a driving force for UO₂ corrosion even under reducing conditions has been examined in leaching tests on low burn-up (low alpha dose-rate) fuel. No significant effect of alpha radiolysis under the experimental conditions was detected. Thermodynamically the calculated uranium solubilities in the pH range 4–8.2 generally agreed well with the measured ones, although assumptions made for certain parameters in the calculations limit the validity of the results.