Carburization of Hastelloy alloy X

The carburization of Hastelloy alloy X has been studied by the standard tracer techniques using ¹⁴C over the temperature range 700 to 1100°C in vacuo and helium environment. The ¹⁴C activity in the specimen decreases exponentially with the depth of penetration and increases with carburization time. It is observed that carbon diffusion in the alloy is dominated by grain-boundary diffusion. The effect of oxygen in helium gas on carburization is observed. Oxygen has two opposite types of action on carburization of the alloy. One is inhibitive action and the other is accelerative action.     

Study on fragmentation behavior of liquid lead alloy droplet in water

Fragmentation behavior of molten lead alloys droplet in water was investigated experimentally by releasing liquid LBE (45w%Pb-55w%Bi) and lead droplets into a pool of subcooled water. The fragmentation occurred when the temperature of the interface between a molten droplet and water was higher than the spontaneous nucleation temperature of water and lower than the minimum film boiling temperature. With increasing the droplet temperatures, the peak pressure in fragmentation of LBE droplet increased from 5 to 8 kPa, and for lead, the value remained around 2 kPa. With increasing the water subcooling, the peak pressure in fragmentation remained constant at 5 kPa for LBE droplet and at 2 kPa for lead droplet. The lead alloy fragmentation process in water was numerically simulated by embedding a semi-empirical fragmentation model for droplet fragmentation rate into the computer code of two-phase flow: JASMINE code. The corresponding results, such as pressure history and fragmentation peak pressure, agreed well with the experimental results.     

Experimental investigation of reaction behavior between carbon dioxide and liquid sodium

Reaction behavior of carbon dioxide (CO₂) with a liquid sodium pool was experimentally investigated to understand the consequences of boundary tube failure in a sodium-CO₂ heat exchanger. In this study, two kinds of experiments were carried out to investigate the reaction behavior.In one experiment, about 1-5 g of liquid sodium pool were poured into flowing CO₂ to obtain the information mainly about the thermo-chemical conditions to initiate the reaction and the chemical constituents of reaction products. During the experiment, visual observation was made using video-camera and the temperature change of the sodium pool and near the surface was measured by thermocouples. The experimental parameters were the sodium pool diameter, the initial temperature of sodium and CO₂, the CO₂ flow direction against pool surface, and the initial moisture concentration in CO₂. The solid products of sodium-CO₂ reaction were sampled and analyzed by X-ray diffraction (XRD), energy dispersion X-ray analysis (EDX), total organic carbon analysis (TOC), and chemical analysis. The reaction gas products were also sampled and analyzed by gas chromatography.In the other experiment, CO₂ was injected into about 200 g of liquid sodium pool to simulate the boundary failure in the sodium-CO₂ heat exchanger. The CO₂ was fed through a helical coil-type tube dipped into the pool to adjust the temperature to the sodium pool temperature, and injected upward into the pool from a pool bottom using a nozzle attached at the end-side of the tube. The experimental parameters were the initial temperature of sodium, the diameter of the nozzle, the flow rate and the injection time of CO₂. The temperature change of sodium pool and the cover gas was measured by thermocouples during the experiment, and the reaction products were sampled and analyzed by the same manner as in the former experiments after the experiment.From these experiments, it became clear that the exothermic reaction occurred above a threshold temperature, and useful and indispensable information such as the resulting temperature and pressure rise and the behavior of solid reaction products in the pool was obtained to evaluate the consequences of boundary tube failure incident in a sodium-CO₂ heat exchanger.     

液态锂锡合金氚增殖行为的理论分析

采用气-液两相界面模型和与时间有关的扩散理论及本征函数展开的方法,模拟了Li25Sn75合金的氚增殖行为.计算结果表明:在14 MeV能量下,天然Sn的(n,2n)反应宏观截面相对较小,只有1.5 b;7Li、6Li产氚随时间变化的规律与LiPb合金、Li2O介质是一致的;Li25Sn75合金对模型厚度比较敏感,随着厚度和6Li丰度的增加,氚增殖比(Tritium Breeding Ratio,TBR)保持上升的趋势.     

The effect of grain boundary engineering on the oxidation behavior of INCOLOY alloy 800H in supercritical water

Grain boundary engineering (GBE) was applied to INCOLOY alloy 800H by means of thermomechanical processing. The oxidation behavior of GBE-treated alloy 800H exposed in supercritical water (SCW) with 25 ppb dissolved oxygen at 500 °C and 25 MPa was significantly improved as compared to 800H in the annealed condition. Gravimetry, optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) were employed in this study to analyze the oxidation behavior of control (annealed) and GBE-treated samples. GBE improves the protective oxidation behavior by enhancing spallation resistance and reducing oxidation rate. Spallation resistance correlates with a reduction in texture of the oxide layers.     

Influence of sodium environment on the uniaxial tensile behavior of titanium modified type 316 stainless steel

True stress-true strain tensile data have been obtained for titanium modified type 316 stainless steel in the solution annealed condition and after exposure to a flowing sodium environment at temperature of 700, 650, 600 and 550°C. The specimens were exposed to sodium for times between 120 and 5012 h to produce carbon penetration depths in the range 0.05–0.30 mm. The Voce equation was used to describe tensile flow curves for plastic strains above 0.005. The results showed that, when compared with solution annealed specimens, the tensile flow behavior of the sodium exposed specimens is characterized by a higher strain hardening rate, which decreases rapidly as the flow stress increases. The loss in tensile ductility of the material due to carburization in sodium environment was found to be minimal.     

Evaluation of anelasticity and plastic creep limit for alloy 800

The elevated temperature tensile, anelastic and creep properties of a precipitation strengthened Ni---Cr austenitic steel (alloy 800) have been evaluated with respect to LMFBR application. These properties have been estimated and formulated for small strains and temperatures on the order of 823 K. It has been shown that despite suppression of the in-service stresses to beneath the alloy's yield strength, plastic deformation will occur at such temperatures and the stress below which plastic strain is effectively zero (plastic creep limit) is negligible for a reactor life time. The plastic creep limit at a given time and temperature markedly depends on the degree of precipitation hardening or prior cold deformation for alloy 800. The contribution from anelastic deformation is less than 0.05% and only becomes important for strict dimensional control and constrained parts.     

Postirradiation tensile behavior of nickel-doped ferritic steels

Tensile specimens of normalized-and-tempered 9Cr-1MoVNb, 9Cr-1MoVNb-2Ni, 12Cr-1MoVW, 12Cr-1MoVW-1Ni, and 12Cr-1MoVW-2Ni steels were irradiated in the High-Flux Isotope Reactor (HFIR) at 300, 400, and 500°C to displacement-damage levels of up to ˜11 dpa. The nickel was added to the ferritic steels to produce helium by a two-step (n, ) reaction during irradiation in this mixed-spectrum reactor. Up to 103 appm He was produced in the steels with 2% Ni. Irradiation at 300 and 400°C caused an increase in strength of all the steels relative to the strength in both the normalized-and-tempered condition and after aging the normalized-and-tempered steel for a time period similar to that in the reactor. The strength increases were accompanied by a loss of ductility. At 500°C, there was little change in the strength properties of the steels. The results at 300 and 400°C indicate an effect of helium on the strength increases; no helium effect was apparent for the specimens irradiated at 500°C.     

The tensile deformation behavior of fine-grained α-plutonium

Tensile deformation of extruded monoclinic α-plutonium with an average grain size of 4 μm was studied at stress from 2 500 to 100 000 psi (17.3 to 689 MN/m²) and temperatures from 22 to 108°C. The strain rate varied from 10^?9 to 7 × 10^?3 sec^?1. The relation, $\text{? = 2.86 × 10}{}^{\mathrm{?7}}\text{σ}{}^{4.2}\text{exp}\text{(?25 600/}\text{RT}\text{)}\text{sec}{}^{\mathrm{?1}}$, was obeyed from 12 000 to 60 000 psi (71.7 to 414 MN/m²) for strain rates greater than about 10^?6 sec^?1. Stress and temperature dependences of creep rate over this stress range were in accord with a dislocation climb controlled creep model, although the power law behavior occurred at stresses higher than theory predicts. The value of 25 600 cal/mole proved a reasonable value for the activation energy for self-diffusion in α-plutonium. At lower stresses the apparent activation energy for creep increased with decreasing stress, and the stress exponent $\text{n}\text{(=}\text{d log}\text{?/}\text{d log}\text{σ)}$ increased from 4.2 to 7.9. The high apparent activation energies for creep and high n values at low stresses were attributed to grain growth during creep. Tensile elongation increased with decreasing strain rate and increasing temperature over the entire stress range. Low elongation at high stresses was attributed to lack of grain boundary sliding. Grain size changed during creep toward a size determined by stress. At the highest test temperatures and lowest stresses grain growth occurred during large strains, while at high stresses the average grain size decreased.     

A study of atomic interaction between suspended nanoparticles and sodium atoms in liquid sodium

A feasibility study of suppression of the chemical reactivity of sodium itself using an atomic interaction between nanoparticles and sodium atoms has been carried out. We expected that the atomic interaction strengthens when the nanoparticle metal is the transition element which has a major difference in electronegativity from sodium. We also calculated the atomic interaction between nanoparticle and sodium atoms. It became clear that the atomic bond between the nanoparticle atom and the sodium atom is larger than that between sodium atoms, and the charge transfer takes place to the nanoparticle atom from the sodium atom. Using sodium with suspended nanoparticles, the fundamental physical properties related to the atomic interaction were investigated to verify the atomic bond. The surface tension of sodium with suspended nanoparticles increased, and the evaporation rate of sodium with suspended nanoparticles also decreased compared with that of sodium. Therefore the presence of the atomic interaction between nanoparticles and sodium was verified from these experiments.Because the fundamental physical property changes by the atomic interaction, we expected changes in the chemical reactivity characteristics. The chemical reaction properties of sodium with suspended nanoparticles with water were investigated experimentally. The released reaction heat and the reaction rate of sodium with suspended nanoparticles were reduced than those of sodium. The influence of the charge state of nanoparticle on the chemical process with water was theoretically investigated to speculate on the cause of reaction suppression. The potential energy in both primary and side reactions changed by the charge transfer, and the free energy of activation of the reaction with water increased. Accordingly, the reaction barrier also increased. This suggests there is a possibility of the reduction in the reaction of sodium by the suspension of nanoparticles. Consequently the possibility of the reaction suppression of sodium itself by the atomic interaction between nanoparticles and sodium atoms, which occurs by suspension of nanoparticles into sodium, was discovered.     

Oxidation behavior of Incoloy 800 under simulated supercritical water conditions

For a correct design of supercritical water-cooled reactor (SCWR) components, data regarding the behavior of candidate materials in supercritical water are necessary. Corrosion has been identified as a critical problem because the high temperature and the oxidative nature of supercritical water may accelerate the corrosion kinetics. The goal of this paper is to investigate the oxidation behavior of Incoloy 800 exposed in autoclaves under supercritical water conditions for up to 1440 h. The exposure conditions (thermal deaerated water, temperatures of 723, 773, 823 and 873 K and a pressure of 25 MPa) have been selected as relevant for a supercritical power plant concept. To investigate the structural changes of the oxide films, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and electrochemical impedance spectroscopy (EIS) analyses were used. Results show changes in the oxides chemical composition, microstructure and thickness versus testing conditions (pressure, temperature and time). The oxide films are composed of two layers: an outer layer enriched in Fe oxide and an inner layer enriched in Cr and Ni oxides corresponding to small cavities supposedly due to internal oxidation.     

Visualization on the behavior of inert gas jets impinging on a single glass tube submerged in liquid sodium

In order to accurately model sodium–water reaction jets in steam generators of fast breeder reactors, knowledge of size distributions or mean diameters of liquid sodium droplets entrained into the reaction jets is prerequisite. In the present study, argon-gas jet behaviors, without chemical reaction, injected into liquid sodium were successfully visualized using an endoscope and a glass tube, and the size distributions and mean diameters of liquid sodium droplets entrained into the gas jet were also obtained in the bubbling regime. Most of the liquid sodium droplets were observed to be intermittently produced in the vicinity of a gas nozzle in the present study. The droplet size distributions of entrained sodium droplets were found to agree well with the Nukiyama–Tanasawa distribution function when the arithmetic mean diameter was used. The Sauter mean diameters obtained in the present study were also found to be well correlated with an empirical equation proposed by Epstein et al. The present study shows that the existing knowledge, which is based on the results of water experiments, is suitable in terms of accuracy in practice.     

High temperature oxidation of cold worked and annealed alloy 800 at low oxygen pressure

The morphology of the oxide formed on Alloy 800 oxidised at a pressure of 10^?5 N/m² oxygen has been studied. Cold worked material was oxidised at temperatures between 870 and 1020 K whilst the effect of vacuum annealing after cold work has been studied at 1020 and 1070 K. The variation in surface composition was followed during oxidation by Auger electron spectroscopy. After oxidation, scanning electron microscopy, electron probe microanalysis and metallographic examinations were carried out. Two modes of oxidation were observed: above and below 1000 K. These are described in terms of diffusion of alloying elements and trace impurities. On the basis of these results an oxidation sequence involving oxide spalling is outlined.     

Determination of solubility of uranium in liquid sodium

An experimental technique has been developed which overcomes the two major problems common to liquid metal solubility measurements, namely, maintaining the integrity of the samples during transfer of the liquid sodium from container to whatever device is used for analysis and detecting solute at very low concentration in liquid sodium. The solubility of uranium in liquid sodium has been measured over the temperature range 150～400℃, by equilibration and sampling technique, the solubility of uranium is approximately 0.00001%.