Corrosion Of Structural Materials Research Articles

Materials Science Analysis of RCCA Structural Materials and Calculations for Lifetime Extension

The paper considers the possibility of lifetime extending of the rod control cluster assemblies in operation by determining their residual lifetime using an approach that takes into account the actual position of the rod control cluster assembly in the core. Excessive conservatism was introduced by assuming that the immersion of the 10th working group in the core during all fuel campaigns is 70 %, while the actual position is 85-90 %. Taking into account the actual position of the rod control cluster assemblies indicates much less irradiation of the lower, most loaded part of control rod cladding and much less burnup of the 10B compared to 70 % immersion of the rod control cluster assemblies, since they are in the area of lower neutron flux density.
 The results of a comprehensive analysis of available studies and test results to determine the phenomena that can potentially approach the achievement of the boundary state of the structural components or limit the lifetime of control rods and rod control cluster assemblies in general are presented. Such phenomena include general corrosion of structural materials (42CrNiMo, Cr18Ni10Ti) (decrease in wall thickness, increased transfer of radioactive corrosion products the coolant); radiation resistance (degradation of mechanical characteristics) of control rod cladding materials (42CrNiMo) and other structural components of the rod control cluster assemblies (42CrNiMo, CrKh18Ni10Ti); radiation resistance of neutron-absorbing materials (B4C, Dy2O3∙TiO2); compatibility of absorbing materials with the control rod cladding.
 Based on the results of post-irradiation examinations of control rods tested in research reactors as dummy rods or rod control cluster assembly rods operated in the VVER-1000 core, the following boundary values were established that can be used as criteria for maintaining the integrity of the control rod cladding: maximum fast neutron fluence in the lower, most loaded part of the control rod cladding (in the weld area of the lower end plug and the cladding) should not exceed 34×1021 n/cm2; maximum burnup of the 10B isotope should not exceed 45 %. If these two criteria are met, the possibility of other potentially damaging phenomena is too low.
 According to the calculations that use the schedule of changes in the position of the rod control cluster assemblies of the control group and the power of one of the power units during one fuel cycle, one can preliminary conclude that the proposed approach will extend the lifetime of almost all rod control cluster assemblies from 25500 to 38000 hours in the automatic control group and from 75600 to 113500 hours in the shutdown group. The residual lifetime should be assessed for a particular power unit and each rod control cluster assembly separately, since each rod control cluster assembly has its own operating history.

Fabrication Aspects and Performance Characterization of α-Al2O3/AlPO4 Based Sandwich Configuration Flow Channel Inserts and Coatings for High Temperature Liquid Metal Applications

Abstract Liquid metals (LMs) exhibit several key characteristics justifying their utilization as coolants and breeders for nuclear fusion reactors and advanced fission reactors. In fusion reactors, the LMs confront an exorbitantly high flow retarding force, due to the magneto-hydro-dynamics (MHD) effect, imposing significant demands on the pumping power and designs of ancillary coolant systems. Corrosion of structural materials leading to activated corrosion products and coolant chemistry control are some of the vital issues common to both fusion and fission reactors employing liquid lead (Pb) and its alloys. To address these concerns, different technological solutions such as flow channel inserts (FCIs) and high temperature compatible corrosion resistant coatings are being investigated to provide a chemical and/or electrical isolation between the LM and structural material for advanced reactors. In this study, three different prototype geometries (circular, square, and 90 deg bend) of steel-insulator-steel sandwich FCIs are fabricated for fusion reactor applications and an extensive characterization of the electrical insulation is performed over an operating temperature range of 100 °C–600 °C. Welding trials and pneumatic pressure tests up to 10 kg/cm2 (g) are performed on the assemblies to validate the electrical and mechanical integrity over typical fusion reactor operational regime. This paper presents detailed fabrication aspects along with quantitative estimations of insulation filling density, electrical insulation performance and, for the first time, a detailed systematic study of insulation degradation resulting from the combined effects of tungsten inert gas (TIG) welding, exposure to pressure and machining operations on these FCIs. The paper also provides critical details derived from the metallurgical examinations and visual observations from the destructive tests executed on the prototypes. Further, from an implementation perspective toward Lead-cooled Fast Reactors (LFRs), a preliminary feasibility assessment of the α-Al2O3/AlPO4 coating is performed through thin film deposition trials on planar and non-planar substrates followed by mechanical characterizations, such as coating thickness, surface roughness, adhesion strength and microhardness. Metallurgical analyses are presented and discussed to assess Pb ingress after 700 h of continuous exposure to molten Pb alloy at 300 °C–400 °C.

Corrosion Mitigation in Molten Salt Environments.

The aim of this paper is to present methods for corrosion mitigation in molten salt environments. The corrosion of structural materials depends directly on the redox potential of the salt. When the redox potential of the salt is higher than the standard potentials of the elements constituting the structural materials, corrosion occurs. If the reverse is true, no corrosion is observed. Herein, a methodology for calculating the theoretical potential of a molten salt is provided and compared with experimental measurements. Three ways to mitigate corrosion by modifying the salt redox potential are proposed: (i) using a soluble/soluble redox system; (ii) using a potentiostatic method; and (iii) using an amphoteric compound such as UCl3, TiCl2, or TiCl3. Immersion tests were conducted under the above conditions to validate the methodology.

Numerical study of solid-state oxygen control bypass performance and corrosion distribution in a LBE flow loop

Liquid lead–bismuth solid-state oxygen control technology is considered to be one of the effective means to inhibit corrosion of structural materials. The dissolution rate of PbO particles in the mass exchanger (MX) is a crucial factor influencing the effectiveness of solid-state oxygen control. To enhance the oxygen control efficiency of the MX, a PbO particle dissolution model based on the UPBEAT (Universal lead(Pb) bismuth(Bi) Eutectic Advanced Test loop) was established. This model aims to determine the impact of temperature, LBE flow rate, operating time, and initial oxygen concentration on the dissolution rate of PbO particles and the steady-state time in the MX. The obtained insights inform the design and operational aspects of the MX. Simultaneously, a loop corrosion precipitation model was developed to simulate loop corrosion in both oxygen-free and solid-state oxygen control states. While the corrosion precipitation distribution in the loop remains consistent between oxygen-free and oxygen-controlled states, solid-state oxygen control effectively enhances the corrosion resistance of the loop.

Effect of Fission Products on Molten Salt Corrosion for Nuclear Reactor Applications

Molten halide salts are used in various technologically important applications like molten salt reactors and concentrated solar power. A major challenge of molten salts is their corrosivity towards structural materials. However, most of the complex interfacial phenomena related to molten salt corrosion are not well understood, primarily due to the complex impact of salt chemistry on structural material interface. Structural material corrosion is influenced by salt redox potential, fission product buildup, presence of impurities and moisture. Given the huge dependence of operations on salt chemistry, understanding the interactions between soluble fission products and structural alloys is of great importance. EuCl3 is one of the primary fission products and shown EuCl3 to cause accelerated corrosion of structural alloys in molten chloride salts. Given the more positive formal oxidation potential of Eu(III)/Eu(II) compared to nickel, iron, and chromium that are major components of the structural alloys, Eu(III) species act as a strong oxidant to cause the dissolution of these metals. This talk will highlight utilization of novel in situ optical spectroscopy technique to study time-dependent evolution of corrosion damage of metals in presence of EuCl3 as well as the EELS technique to identify changes in oxidation states of dissolved alloying elements.

Microorganisms Involved in the Biodegradation and Microbiological Corrosion of Structural Materials

Microbiologically influenced corrosion (MIC) is the process of material degradation in the presence of microorganisms and their biofilms. This is an environmentally assisted type of corrosion, which is highly complex and challenging to fully understand. Different metallic materials, such as steel alloys, magnesium alloys, aluminium alloys, and titanium alloys, have been reported to have adverse effects of MIC on their applications. Though many researchers have reported bacteria as the primary culprit of microbial corrosion, several other microorganisms, including fungi, algae, archaea, and lichen, have been found to cause MIC on metal and non-metal surfaces. However, less attention is given to the MIC caused by fungi, algae, archaea, and lichens. In this review paper, the effects of different microorganisms, including bacteria, fungi, algae, archaea, and lichens, on the corrosion properties of engineering materials have been discussed in detail. This review aims to summarize all of the corrosive microorganisms that directly or indirectly cause the degradation of structural materials. Accusing bacteria of every MIC case without a proper investigation of the corrosion site and an in-depth study of the biofilm and secreted metabolites can create problems in understanding the real cause of the materials’ failure. To identify the real corrosion agent in any environment, it is highly important to study all kinds of microorganisms that exist in that specific environment.

Thermodynamics of corrosion products in molten nitrate salts

Structural material corrosion is one of the major concerns regarding the implementations of molten salt technologies and thermodynamic calculation is crucial to understand the corrosion mechanism occurring in molten salts. The present study unlocked the limits of thermodynamic calculations in molten nitrate salt systems by using a new reference state. Based on which, the Ellingham and E-pO2− diagrams for the corrosion products including Cr, Fe, Mn, and Ni were developed, unveiling the stability domains of these metals and the various overall equilibria which may participate in the corrosion and passivation process in molten nitrate salts.

Weld corrosion of GH3535 in molten (Li,Na,K)F

The corrosion of structural materials in molten fluoride salts restricts the development of a molten salt reactor (MSR), with local galvanic corrosion of the weld joint being one of the major failure modes associated with the structural materials in the operating environment of an MSR. In this paper, in situ electrochemical measurements, combined with scanning electron microscopy (SEM/EDX) and metallographic microscope testing methods, are used to study the weld corrosion of GH3535 at 700 degrees C in molten (Li,Na,K)F. The results show that each part of the welding areas is in active dissolution state at the open circuit potential. The electrochemical behavior of the heat affected zone is similar to that of the GH3535 parent material. When the weld zone of the GH3535 is coupled with the parent alloy, galvanic corrosion occurs and the galvanic corrosion effect is larger than 1.

Corrosion and aging risk assessment of an injection system for FCC/Bio-oil co-feed

Fast pyrolysis oil (FPO) is a renewable biocrude with high corrosivity and poor thermal stability. Co-processing FPO with petroleum intermediates in existing fluid catalytic cracking (FCC) units is one of the most applicable methods for transforming low-quality biocrudes into drop-in fuels. Although FPO is immiscible with petroleum intermediates, co-processing can be achieved using two separate feeding lines for FCC injection instead of the premixture. However, the corrosion of structural materials and the thermal stability of FPO pose significant challenges to the co-processing feed injection system, as the feedstocks are usually preheated to 100–300 °C prior to injection. This study focuses on the corrosion of stainless steel (SS) 316L and evaluates the aging risk of FPO at a temperature range of 80–220 °C. SS 316L experienced noticeable degradation with increasing temperature. Corrosion rates of 0.06, 0.62, and 1.77 mm/y were observed at 80, 150 and 220 °C, respectively. The experimental observation also reveals phase separation (liquid and solid phase) of FPO at the experimenting temperatures. However, the change in the physicochemical properties of the phases becomes more significant as temperature increases. Furthermore, a critical temperature of about 80 °C was identified, which signifies both the onset of active corrosion of SS 316 L in FPO and the fast aging of FPO.

Viability of Cathodic Protection for Preventing Corrosion of Stainless Steel 316H in Molten LiF-NaF-KF

Molten fluoride salts are candidate heat transfer fluids in a number of applications such as generation IV molten salt nuclear reactors and concentrated solar power plants. However, a chief concern in the design of these systems is the corrosion of structural materials that come in contact with these molten salts. Redox control methods such as the purification of salt, the addition of active elements, and applied electrochemical potential can be efficient methods for preventing the corrosion of structural materials in molten fluoride salts. Applied electrochemical potential as a redox control method for application in molten fluoride salts has rarely been explored. This study seeks to understand the viability of impressed current cathodic protection (CP) at various currents as a redox control method to prevent corrosion of stainless steel 316H in molten LiF-NaF-KF (FLiNaK) salt. Results show that application of CP can be an effective method to prevent corrosion of SS316H in molten FLiNaK salt, but the applied current will have to be optimized to prevent undesirable side effects such as reduction of salt constituents, salt deposition on electrodes, etc.

Corrosiveness of Li2TiO3 ceramic tritium breeder to structural RAFM steel: Effects on microstructure and thermal conductivity

Structural steel will be in long-term contact with ceramic tritium breeder at a high temperature in a solid tritium breeding blanket. The maximum temperature in the tritium breeding zone would reach nearly 1173 K. At this high temperature, a large amount of lithium oxide would evaporate and deposit on the structural materials, causing the overall corrosion of the structural materials. Corrosiveness of Li2TiO3 ceramic tritium breeder to reduced activation ferritic-martensitic steel CLF-1 was investigated in this study. The experiment was carried out at 1123 K under He + 0.1 vol% H2 atmosphere for up to 400 h. The formation of non-uniform corrosion layers with a Fe-rich outer layer and a Cr-rich inner layer were found on the surface of CLF-1 steel. Secondary ion mass spectrometry (SIMS) test at contact and non-contact areas were performed to demonstrate evaporation of lithium compound. The corrosion layers were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The non-contact area with tritium breeding pebbles were corroded indicating a large amount of lithium oxide on the non-contact zone, resulting in serious overall corrosion of structural materials. LiFe5O8 was found as the main phase on the surface of the corroded samples by X-ray diffraction (XRD). The thermal conductivity of LiFe5O8 (∼0.8 W/m/K, 300 K) calculated by first principles phonon Boltzmann equation (PBE) is significantly lower than the original CLF-1 (∼23 W/m/K, 300 K). Almost no change of thermal conductivity for experimental results was found after corrosion, which is due to non-uniform corrosion layer presenting thinner layer at some areas, as well as the hole, crack and peeling of corrosion layer indicated by SEM results. However, in the long-term service of blanket structural material, it is predicted that a much thicker corrosion layer may form on the surface of RAFM steels thus bring a risk to the heat transfer of blanket.

Effect of metal fluorides on the corrosion of structural materials in molten LiF-NaF-KF

The corrosion of structural materials in molten fluoride salts is predominantly caused by the presence of impurities in the salt. This study focuses on understanding the corrosion behavior of selected alloys in molten FLiNaK salt with addition of similar quantities of metal fluoride impurities such as CrF2, CrF3, FeF2, FeF3, and NiF2. The results show that the presence of selected metal fluoride impurities increases the extent of corrosion of the selected alloys in molten FLiNaK salt, with the exact effect depending on the thermodynamic stability of the fluoride impurity added as well as the composition of the structural alloy studied.

Electrochemical Sensors for Controlling Oxygen Content and Corrosion Processes in Lead-Bismuth Eutectic Coolant-State of the Art.

Controlling oxygen content in the primary circuit of nuclear reactors is one of the key tasks needed to ensure the safe operation of nuclear power plants where lead-bismuth eutectic alloy (LBE) is used as a coolant. If the oxygen concentration is low, active corrosion of structural materials takes place; upon increase in oxygen content, slag accumulates due to the formation of lead oxide. The generally accepted method of measuring the oxygen content in LBE is currently potentiometry. The sensors for measuring oxygen activity (electrochemical oxygen sensors) are galvanic cells with two electrodes (lead-bismuth coolant serves as working electrode) separated by a solid electrolyte. Control of corrosion and slag accumulation processes in circuits exploring LBE as a coolant is also based on data obtained by electrochemical oxygen sensors. The disadvantages of this approach are the low efficiency and low sensitivity of control. The alternative, Impedance Spectroscopy (EIS) Sensors, are proposed for Real-Time Corrosion Monitoring in LBE system. Currently their applicability in static LBE at temperatures up to 600 °C is shown.

Analysis of the effect of pollution of component surfaces as a result of possible contact of fresh nuclear fuel with sea atmosphere on corrosion

Acquisition and analysis of the information was performed on possible effect of components of sea atmosphere in case of their precipitation on the assembly surfaces on the corrosion of structural materials of items of fuel assemblies (FAs) of water-water energetic reactor (VVER-1000) in their subsequent operation. The data is presented on static and dynamic tests of alloy E-110 at temperatures of 300–350 С in water and standard coolant of the reactor polluted with chlorides and iodine, as well as of alloy E-110 under special pollution of its surface with chlorides. It is demonstrated that in keeping the conditions of storage of fresh fuel, as well as the recommendations of the present work, its high corrosion resistance and operability in further operation is ensured.

Corrosion of structural materials for salt melt technologies

Molten salt mixtures are considered media for many modern technologies using their ability to store thermal energy, thermal stability at high temperatures, low melting point, and other properties. The disadvantage of their use is high corrosion aggressiveness towards metal structural materials. In particular, impurities contained in salt mixtures can significantly increase the corrosion rates of alloys. This paper compares the corrosion behaviour of Inconel 625, 321, 316L and 316Ti alloys in a mixture of chloride and nitrate salt melts. The parameters in which both mixtures are stable and in melt form were chosen -400 °C, an inert argon atmosphere, and a pressure of 0.2 MPa. After exposure, the state and composition of the surfaces were analysed by XPS (X-ray photoelectron spectroscopy) and SEM (Scanning Electron Microscopy). These materials are better suitable for nitrate salt environments, where only very thin surface layers were formed without local types of corrosion. In chloride melts, Alloy 321 and Inconel 625 have shown greater resistance than 316L and 316Ti stainless steels.

Point Defect Model for the kinetics of oxide film growth on the surface of T91 steel in contact with lead–bismuth eutectic

Point Defect Model (PDM) has been successfully employed for aqueous solutions to describe the rate of surface corrosion of structural materials. In this work, the adaptation of PDM for the case of lead–bismuth coolant is developed. The necessary modifications in the set of electrochemical reactions and in the model of electrostatic potential distribution in the oxide film are made. Parameters of the proposed model, PDM_PB, are optimized using the experimental data for T91 grade steel. The obtained adaptation of PDM shows applicability to the case of lead and lead–bismuth coolants which is of critical importance for the next-generation fast-neutron reactors.

Deposition of Colloidal Magnetite on Stainless Steel in Simulated Steam Generator Conditions—Experiments and Modeling

Sludge formation via colloidal magnetite deposition in steam generators is an important phenomenon that significantly influences the thermohydraulic properties and corrosion of structural materials. This paper aims to verify a model of sludge deposition and consolidation with emphasis on its most significant parameters and their experimental estimation. In-situ electrochemical impedance spectroscopic (EIS) measurements are employed for quantitative evaluation of magnetite deposition kinetics on stainless steel in ammonia-ethanolamine (AMETA) secondary coolant at different temperatures. Parameterization of the model by quantitative comparison of the mixed-conduction model (MCM) with experimental data is discussed. Model predictions are compared with literature data from laboratory experiments and plant operation. Conclusions are drawn about the applicability of the model for quantitative assessment of sludge deposition and consolidation rates.

Alkali Chloride Molten Salt Corrosion Testing Using a Rotating Cylindrical Electrode

Next generation nuclear reactors utilizing alkali chloride molten salts are currently under development. These reactors operate at a higher temperature and more efficient than current nuclear reactors. Molten salt reactors necessitate research to develop knowledge of corrosion of the structural materials for this application. Static corrosion tests may fail to account for the effects that fluid flow may have on corrosion and molten salt flow loops can be complex and uneconomical. A rotating cylindrical electrode (RCE) can simulate the effects of flow on the corrosion of structural components and are more elementary than a flow loop. We have developed a rotating cylindrical electrode apparatus to study the effects flow may have on corrosion of structural materials in alkali chloride molten salts using accelerated electrochemical corrosion testing techniques and surface characterization techniques which are then compared to static alkali chloride molten salt corrosion. Results and analysis of the effects of fluid flow on accelerated electrochemical corrosion of structural materials will be presented.Acknowledgement:This research is being performed using funding received from the DOE Office of Nuclear Energy's Nuclear Energy University Programs under awards DE-NE0008889 and DE-NE0008236, and the US Nuclear Regulatory Commission (USNRC) under contract 31310018M0032. Dr. Kenny Osborne and Ms. Nancy Hebron-Isreal serve as the program managers for the DOE and NRC awards, respectively.

Corrosion Testing in Nitrate Molten Salt Using Rotating Cylindrical Electrode

Molten salts are under consideration as the working fluid in thermal power generation. Nitrate molten salts store vast amounts of energy at high temperature and are an efficient energy production medium. Nitrate molten salts are corrosive to structural materials in these applications. Static corrosion studies may neglect the effects of fluid flow on corrosion and flowing test loops can be expensive and complex. A rotating cylinder electrode (RCE) can simulate the effects of fluid flow on the corrosion of structural materials and are more compact and economical then flow loops. We have developed a rotating cylinder electrode apparatus to study the corrosion of structural metals in flowing molten salts using accelerated electrochemical corrosion testing. In this study, we have evaluated the corrosion behavior in molten nitrate salts and used various surface characterization techniques to compare the results from static corrosion tests. Results and analysis of these studies will be presented.Acknowledgement:This research is being performed using funding received from the DOE Office of Nuclear Energy's Nuclear Energy University Programs under awards DE-NE0008889 and DE-NE0008236, and the US Nuclear Regulatory Commission (USNRC) under contract 31310018M0032. Dr. Kenny Osborne and Ms. Nancy Hebron-Isreal serve as the program managers for the DOE and NRC awards, respectively.

Assay of nuclear grade primary sodium in the fast breeder test reactor for radionuclides and corrosion elements

Periodic assay of primary sodium used as a coolant in the fast breeder test reactor (FBTR) at Kalpakkam is necessary and pre-requisite for the safe and continuous operation of the reactor. Contamination of nuclear grade purity of the primary sodium is monitored either online or offline for the radionuclides and chemical impurities to ascertain the integrity of the various components. Chemical elements which can entrain into sodium due to the corrosion of structural materials is troublesome as they might clog the coolant channels resulting in to a reduced coolant flow which further leads to fuel clad failure. The corrosion elements present in the primary sodium were determined by ICP-OES and their activation products were assayed by high resolution gamma spectrometry. In case of fuel clad rupture, the fission products such as 137Cs, 134Cs, 136Cs, 131I, 90Sr, 125Sb etc. along with actinides U and Pu are released into primary sodium. This paper reports actinides, fission products, corrosion elements as well as their activation products and concentration levels present in the primary sodium of FBTR. Activity variation of one of the long-lived fission products, viz. 137Cs over the period of time, before and after fuel clad rupture is profiled and discussed.