Effect of Fe irradiation on the corrosion of 321 stainless steel at high-temperature CO2: Different oxidation responses of δ-ferrite and austenite to irradiation damage

Long-Term Effects of 56Fe Irradiation on Spatial Memory of Mice: Role of Sex and Apolipoprotein E Isoform

The environmental cracking of Type 316 austenitic stainless steel manual metal arc (MMA) weldments in high temperature CO2 has been investigated. The welding thermal transient has been analyzed and used to predict the sensitization of the parent material and resulting residual stresses. Sensitization is considered to result from the local depletion of chromium about grain boundaries and this has been considered theoretically and measured using STEM combined with energy dispersive X-ray analysis. Residual stresses have been measured using the X-ray diffraction method. Flux residues over the HAZ of the weldment have been identified using X-ray diffraction analysis. Chemical changes in these residues which resulted in cracking of test samples exposed to high temperature (673 to 823 K) CO2 gas have been analyzed by X-ray diffraction. The susceptibility of the weldments to cracking was found to be influenced by the carbon content and hardness of the material. In materials of high carbon content and high hardness, the necessary cracking parameters are satisfied by the combined contribution of the microstructural sensitization, tensile residual stresses, and the chemical interaction of weld flux residue with the CO2 gas which provides a molten salt environment capable of allowing rapid transport of aggressive species to active crack sites.

Relatively little is known about early irradiation effects on hippocampal function in wild-type mice. In this study, the effects of (56)Fe irradiation on hippocampal function were assessed starting 2 weeks after whole-body irradiation. Compared to sham irradiation, radiation impaired novel object recognition in female and male C57BL/6J wild-type mice. There were no effects of irradiation on contextual fear conditioning or spatial memory retention in the water maze. It is possible that oxidative damage might contribute to radiation-induced cognitive changes. Therefore, hippocampal and cortical levels of 3-nitrotyrosine (3NT) and lipid peroxidation, measures of oxidative damage were assessed. There were no effects of irradiation on these measures of oxidative damage. As (56)Fe irradiation can increase reactive oxygen species (ROS) levels, which may contribute to the impairments in novel object recognition, the effects of the antioxidant alpha-lipoic acid (ALA) on cognition following sham irradiation and irradiation were also assessed. ALA did not prevent radiation-induced impairments in novel object recognition and impaired spatial memory retention of sham-irradiated and irradiated mice in the probe trial after the first day of hidden platform training in the water maze. Thus, the novel object recognition test is particularly sensitive to detect early cognitive effects of (56)Fe irradiation through a mechanism unlikely involving ROS or oxidative damage.

Effects of irradiation on hippocampal function have been mostly studied in male rodents and relatively little is known about potential effects of irradiation on hippocampal function in female rodents. Moreover, although the long-term effects of clinical radiation on cognitive function have been well established, the effects of other forms of irradiation, such as high charged, high energy radiation (HZE particles) that astronauts encounter during space missions have not been well characterized. In this study we compared the effects of (56)Fe irradiation on fear conditioning in C57BL/6J female and male mice. Hippocampus-dependent contextual fear conditioning was impaired in female mice but improved in male mice following (56)Fe irradiation. Such impairment was not seen for hippocampus-independent cued fear conditioning. Thus, the effects of (56)Fe irradiation on hippocampus-dependent contextual fear conditioning are critically modulated by sex.

This project aimed at synthesis of a new inorganic dual-phase carbonate membrane for high temperature CO{sub 2} separation. Metal-carbonate dual-phase membranes were prepared by the direct infiltration method and the synthesis conditions were optimized. Permeation tests for CO{sub 2} and N{sub 2} from 450-750 C showed very low permeances of those two gases through the dual-phase membrane, which was expected due to the lack of ionization of those two particular gases. Permeance of the CO{sub 2} and O{sub 2} mixture was much higher, indicating that the gases do form an ionic species, CO{sub 3}{sup 2-}, enhancing transport through the membrane. However, at temperatures in excess of 650 C, the permeance of CO{sub 3}{sup 2-} decreased rapidly, while predictions showed that permeance should have continued to increase with temperature. XRD data obtained from used membrane indicated that lithium iron oxides formed on the support surface. This lithium iron oxide layer has a very low conductivity, which drastically reduces the flow of electrons to the CO{sub 2}/O{sub 2} gas mixture; thus limiting the formation of the ionic species required for transport through the membrane. These results indicated that the use of stainless steel supports in a high temperature oxidative environment can lead to decreased performance of the membranes. This revelation created the need for an oxidation resistant support, which could be gained by the use of a ceramic-type membrane. Work was extended to synthesize a new inorganic dual-phase carbonate membrane for high temperature CO{sub 2} separation. Helium permeance of the support before and after infiltration of molten carbonate are on the order of 10{sup -6} and 10{sup -10} moles/m{sup 2} {center_dot} Pa {center_dot} s respectively, indicating that the molten carbonate is able to sufficiently infiltrate the membrane. It was found that La{sub 0.6}Sr{sub 0.4}Co{sub 0.8}Fe{sub 0.2}O{sub 3-{delta}} (LSCF) was a suitable candidate for the support material. This support material proved to separate CO{sub 2} when combined with O{sub 2} at a flux of 0.194 ml/min {center_dot} cm{sup 2} at 850 C. It was also observed that, because LSCF is a mixed conductor (conductor of both electrons and oxygen ions), the support was able to provide its own oxygen to facilitate separation of CO{sub 2}. Without feeding O{sub 2}, the LSCF dual phase membrane produced a maximum CO{sub 2} flux of 0.246 ml/min {center_dot} cm{sup 2} at 900 C.

Martensitic stainless steel (UNS S41000), austenitic stainless steel (UNS S31000), and nickel-based alloy (UNS N06625) specimens were exposed at 450°C and 7.6 MPa in pure supercritical CO2 (sCO2) for two months. The exposure was performed in order to assess the effect of various variables on the oxidation of materials that may be used in oxy-combustion gas turbine systems using supercritical CO2. While variables such as temperature, coatings, contaminants, and pressure have been covered in the literature, other variables of potential interests, such as welding, stress corrosion cracking, galvanic issues, or crevices have not yet been studied. The impact variables on oxidation in high temperature sCO2, based on real life engineering designs, were assessed during this exposure. Welding is considered to be of interest due to changes to the local microstructure at high temperature in the vicinity of the weld. Chromium diffuses to the grain boundaries, leaving a chromium-depleted area in the matrix nearby, resulting in a potential decrease in corrosion resistance. Galvanic corrosion may be an issue when nickel alloys and stainless steel are connected. It has been suggested in the literature that galvanic corrosion may not be an issue because sCO2 is not considered an electrolyte, but it has not yet been confirmed experimentally. Stress corrosion cracking might be an issue combining the oxidation occurring in sCO2 and the high pressure present, leading to accelerated crack growth of a susceptible material due to its microstructure. All martensitic stainless steel specimens (plain, welded, or coupled) had a matt black surface finish after the two months exposure. The austenitic stainless steel and the nickel alloy were both discolored after the exposure. Mass gain inspection of the specimen was performed before and after exposure. The highest mass gain was found for the martensitic stainless steel, ten times higher than the austenitic stainless steel and nickel alloy. The welded specimens of martensitic and austenitic stainless steels showed mass gains up to 50% higher than for the non-welded specimens. The mass gains of the coupled materials (galvanic coupling or similar crevice coupling) were not different from that of the single specimens but significant corrosion bonding was observed in all couples. None of the U-bend martensitic stainless steel specimens showed signs of cracking.

This article is focused on the effect of temperature on the corrosion electrochemical behavior of 13Cr martensitic stainless steel under a high temperature and high CO2 partial pressure environment. Cyclic polarization(CP) measurements,electrochemical impedance spectroscopy(EIS),Mott-Schottky plot measurements,ZSIMPWIN software,and scanning electron microscopy(SEM) are used in this study. The results show that the stability of passive films formed on the 13Cr stainless steel surface decreases with increasing temperature under a high temperature and high CO2 partial pressure environment. This leads to increases in the corrosion rate and pitting susceptibility.

The supercritical carbon dioxide (sCO2) Brayton cycle is a promising candidate for future nuclear reactors due to its ability to improve power cycle energy conversion efficiency. The sCO2 Brayton cycle can operate with an efficiency of 45-50% at operating temperatures of 550-700 C. One of the greatest hurdles currently faced by sCO2 Brayton cycles is the corrosivity of sCO2 and the lack of long-term alloy corrosion and mechanical performance data, as these will be key to enhancing the longevity of the system, and thus the levelized cost of electricity. Past studies have shown that sCO2 corrosion occurs through the formation of metal carbonates, oxide layers, and carburization, and alloys with Cr, Mo and Ni generally exhibit less corrosion. While stainless steels may offer sufficient corrosion resistance at the lower range of temperatures seen by the sCO2 Brayton cycles, more expensive nickel-based alloys are typically needed for the higher temperature regions. This study investigates the effects of corrosion on the Haynes 230 alloy, with a preliminary view on changes in the mechanical properties. High temperature CO2 is used for this study as the corrosion products are similar to that of supercritical CO2, allowing for an estimation of the susceptibility towards corrosion without the need for high pressure experimentation.

Effect of laser shock peening and surface mechanical attrition treatment on the oxidation resistance of a 20Cr-25Ni-Nb stainless steel

; 5 8 : 5 : 8 : : 9 < 6 8 9 6 8 6 5 ; 8 6 : 4 9 > < D ; lattice atom was investigated in detail. The results are of general interest since the method used is limited only by the validity of the interatomic potential assummed. Cross sections for the displacement of lattice atoms by gamma rays up to 5 Mev were calculated. A theoretical study was made of the slowing down process for a primary displaced atom in a solid. The small amplitude motion of dislocation loops was investigated in detail, taking into account the whole elastic field interaction between different parts of the loop. The extension and interval correlations in a radiation-induced displacement cascade were investigated. The numerical data apply to copper. A special model for annealing of defects in solids is discussed. Dislocation Interactions: Studies were made of the variations of internal friction and elastic modulus during irradiation of pure copper crystals at a number of temperatures in the range 90 to 300 deg K. Using neutron irradiation as a tool, it is shown that there are at least two dislocation contributions to the Young's modulus and internal friction of Cu at low temperatures. An apparatus was developed which makes possible the continuous observation of the Young's modulus and internal friction of a metal sample. Low-temperature Irradiation Studies: Activation energies for the annealing of copper and aluminum following reactor bombardment near 4 deg K were measured. Isochronal annealing studies of Cu, Ag, Au, Pt, and Zn were made after neutron bombardment of these materials at 4 deg K. It was confirmed that the residual resistivity of high purity copper can be greatly reduced by annealing in an oxidizing atmosphere. A redetermination of the stored-energy release in reactorirradiated Cu between 30 and 50 deg K was made. The design of a new facility for irradiation damage experiments at very low temperatures is described. A helium-cooled facility was installed in the pool of the ORR, which allows samples to be irradiated at about 50 deg C in an inert atmosphere. Electron Microscope Studies: Fission fragment tracks in thin films of UO/sub 2/ were studied and found to be essentially a surface effect in which material at the surface is displaced as a result of the passage of the fission fragments. An improved replication technique for copper is described. Chemical Properties of Metal Surfaces: The kinetics of the dissolution of copper crystals in aqueous solutions were investigated. The diffusion of deuterium in deuteron-irradiated Cu was studied in the temperature range -50 < T < 50 deg C by monitoring neutrons from the D(d,n)He/sup 3/ reaction. Alloy Studies: Experiments were conducted on the effect of irradiation on atomic rearrangements in Cu-Al, Ni-Be, Ni-Cu, Au-Cd, and Fe-C. Semiconductor Studies: A model for the potential well surrounding disordered regions in neutron-irradiated Ge and Si is discussed. The different effects of Co/sup 60/gammaray and fast-neutron bombardment on the electrical behavior of Ge are discussed in terms of the distribution of lattice defects. Thermal neutron capture in Si and Ge is considered. The effect of neutron and gamma irradiation upon minority carrier lifetime in Ge was studied. The effect of 14-Mev neutron irradiation upon the electrical properties of Ge was studied. A preliminary study was made of the change in thermoelectric power of n-type germanium as a result of neutron irradiation. Annealing of radiation-induced conductivity changes in n-type Ge was found to take place in the range between 77 and 273 deg K. The charge-center concentration as a function of temperature of high-purity, n-type Ge under fast- neutron irradiation is compared to similar data obtained for Co/sup 60/ gamma-ray irradiations. The difiusivity, solid solubility, and acceptor behavior of Cu in Ge was investigated. The effect of neutron spectrum on conluctivity changes in n- type Ge was investigated. Hall coefficient and Hall mobility were

The application limit for “modified” 13%Cr martensitic stainless steel (0.025C-13Cr-Ni-Mo) pipe and “conventional” 13%Cr steel (0.2C-13Cr) pipe in high temperature and high CO2 partial pressure environments is clarified. The critical CO2 partial pressure for modified 13%Cr steel pipe usage was significantly improved, being more than 15 MPa at 150 degree C comparing with that for conventional 13%Cr steel pipe of 0.5 MPa or less. Cr is most effective alloying element to prevent the CO2 corrosion at high temperature, and the CO2 corrosion resistance for modified 13%Cr steel pipe at severe sweet environment was evaluated by the equation of that CCI (CO2 corrosion Index) = Cr + 0.2 Ni + 0.25 Mo – 20C. The thin and tight surface films with concentration of Cr, Ni and Mo prevent the corrosion reaction at the steel surface and reduce the corrosion rate of steel at severe sweet environment.

Radiation-induced inhibition of thymidine incorporation in vivo as a measure of the initial slope and RBEn/γ

Fe-20Cr-25Ni-Nb steel is an important material for developing highly compact and efficient nuclear power systems by using the supercritical CO2 Brayton cycle. The in-core materials should possess excellent oxidation resistance in a high-temperature CO2 environment. In this work, a new 20Cr-25Ni-Nb steel with a minor Mo addition was developed, and its oxidation behavior was investigated in a pure CO2 environment at 650 °C under 3.5 MPa. The experimental results show that the oxidation kinetics of the steels followed the parabolic law with the test time, and the oxidation process was controlled by diffusion. The 20Cr-25Ni-Nb steel showed better oxidation resistance after Mo addition, which was attributed to the synergistic effects of Nb and Mo during the oxide scale formation process. In a high-temperature environment, the volatilization of Mo promoted the outward diffusion of Nb, resulting in the formation of an Nb-rich layer at the oxide/metal interface, which slowed the outward diffusion of Fe for the formation of the outermost Fe-oxide layer. Although the volatile nature of Mo at high temperatures promoted the outward diffusion of Nb, the addition of Mo had no significant influence on the overall structure of the oxide scales, which consisted of an outer Cr-rich oxide layer and an inner spinel oxide layer.

While the effects of irradiation on the mechanical properties of stainless steels have been extensively investigated, most data have been obtained from relatively large specimens. However, fusion reactor materials development will require the extensive use of miniaturized specimens. Yet the synergisms between the influence of specimen size and irradiation are not well understood. Consequently, the objectives of this study were to identify and clarify the potential roles of irradiation and specimen size in tensile and creep properties of austenitic stainless steels; this is an initial step in developing a complete understanding of irradiation effects in small specimens.

Many components used in the pressure vessel of French pressurized water reactors are made of austenitic stainless steels : 316L for screws, 304L for core barrel and baffle assembly, etc. Among these components, the most irradiated ones undergo an average damage rate of about 1 dpa/an at temperatures which may reach about 400°C. Such irradiations may have very detrimental effects on the in-service behaviour of austenitic steels. In order to forecast these effects, Electricité de France has defined important programmes of studies. In the framework of these programmes, we have carried out a review concerning the effects of irradiations at relatively low temperatures (i. e. 500°C) on cold-worked 316 stainless steel. We were particularly interested in the evolution of microstructure as well as tensile (with or without notch), creep, fatigue (with or without creep) and fracture toughness properties. In some cases, we have also analysed the influence of cold-work level, irradiation temperature and test temperature. For some mechanical properties, the data was sufficient to qualitatively predict the properties of cold worked 316 stainless steels after long — term irradiations under PWR conditions.