Effect of nitrate on corrosion of austenitic stainless steel in boiling nitric acid solution containing chromium ions

The oxidation behavior of chromium and the corrosion behavior of austenitic stainless steel in boiling nitric acid solution containing highly concentrated nitrates were investigated using UV-visible spectroscopic measurements, Raman spectral measurements, immersion tests, and potentiodynamic polarization measurements. The oxidation rate measurement of chromium from Cr(III) to Cr(VI) was performed by 1 M boiling nitric acid solution containing each highly concentrated nitrates: Al(NO₃)₃, Nd(NO₃)₃, Ca(NO₃)₂, Mg(NO₃)₂, and NaNO₃ as a simulant of uranium nitrate in uranium concentrator in reprocessing plants. As a result, the rate of chromium oxidation was different depending on the added nitrates even at the same nitric acid concentration. In addition, the oxidation rate of chromium was increased with increasing the calculated partial pressure of nitric acid in consideration of the hydration of cation of nitrates. Furthermore, the corrosion rate of type 310 stainless steel was accelerated by the solution having a high chromium oxidation rate containing nitrates. These results indicated that the acceleration of the corrosion rate in the solutions depending on the oxidation rate of chromium, and the rate is affected by the salt-effect of nitrates.     

Effect of re-oxidation rate of additive cations on corrosion rate of stainless steel in boiling nitric acid solution

The boiling nitric acid solution containing highly oxidizing cations dissolved from the spent nuclear fuels corrodes stainless steels because of the nobler corrosion potential and their fast reduction rate. The cations themselves are re-oxidized to higher oxidizing states in a bulk solution after the corrosion reaction. In this paper, the re-oxidation rate constants of typical cations, such as Cr, V, Pu, and Np, were analyzed, and discussed about the effect on time dependencies of the corrosion rate. It was indicated that the cations with a large re-oxidation rate constant, such as Np, could keep the corrosion rate at high level continuously for the long immersion duration.     

Effect of seawater components on corrosion behavior of SUS316L in nitric acid solution containing metal ions

During the accident that occurred at the Fukushima Daiichi nuclear power plant, a large volume of seawater was introduced as coolant into the storage pools for spent nuclear fuel. If this fuel is reprocessed, some components of seawater will be mixed with the nitric acid solution containing metal ions in the reprocessing process where stainless steels are used as structural material. In this study, we investigated the effect of seawater components in high active liquid waste (HAW) containing nitric acid and metal ions as fission products on the corrosion behavior of SUS316L stainless steel.

Corrosion tests were conducted in surrogate HAW containing artificial seawater (ASW). Intergranular corrosion was observed in the HAW with ASW, where Ru increased the corrosion potential to the transpassive region. An increase in the amount of ASW led to a decrease in the corrosion rate and suppression of intergranular corrosion. Interactions between Ru ions and seawater components, such as chloride ions, were indicated by the results of extended X-ray absorption fine structure spectroscopy and cyclic voltammetry analyses of the solution containing ASW and HAW.     

The effect of Nb additive on Te-induced stress corrosion cracking in Ni alloy: a first-principles calculation

Nb can improve the resistance of Ni-based Hastelloy N alloy to Te-induced intergranular embrittlement. First-principles calculations are performed to research this mechanism by simulating the Ni（111） surface and the ∑ 5（012） grain boundary. The calculated adsorption energy suggests that Te atoms prefer diffusing along the grain boundary to forming the surface-reaction layer with Nb on surface of the Ni alloy. First-principles ten- sile tests show that the Nb segregation can enhance the cohesion of grain boundary. The strong Nb-Ni bonding can prevent the Te migration into the inside of the alloy. According to the Rice-Wang model, the strengthen- ing/embrittling energies of Nb and Te are calculated, along with their mechanical and chemical components. The chemical bonds and electronic structures are analyzed to uncover the physical origin of the different effects of Te and Nb. Our work sheds lights on the effect of Nb additive on the Te-induced intergranular embrittlement in Hastelloy N alloy on the atomic and electronic level.     

The effect of radiation on the valence state of plutonium in nitric acid solutions

We investigated the effect of x -radiation on the valence state of plutonium in nitric acid solutions from 0.3 to 2.0 M and also in 0.3 M nitric acid solutions containing varying concentrations of UO₂(NO₃)₂ and K₂Cr₂O₇. The effect of radiation on nitric acid solutions, not containing UO₂(NO₃)₂, causes only oxidation of plutonium and the oxidation yield decreases with an increase in the concentration of NO ₃ ^– ions and acidity of the solution. We put forward the hypothesis that the oxidation is effected by OH radicals. Under certain conditions the reduction of plutonium was observed in the presence of UO₂(NO₃)₂. Apparently, it is not effected by atomic hydrogen but by UO ₂ ⁺ ions. Potassium dichromate causes an acceleration in radiation oxidation of plutonium but under the given conditions it does not retard its reduction.     

The effect of a changing fuel solution composition on a transient in a fissile solution

This paper presents an extension to a point kinetics model of fissile solution undergoing a transient through the development and addition of correlations which describe neutronics and thermal parameters and physical models. These correlations allow relevant parameters to be modelled as a function of time as the composition of the solution changes over time due to the addition of material and the evaporation of water from the surface of the solution. This allows the simulation of two scenarios. In the first scenario a critical system eventually becomes subcritical through under-moderation as its water content evaporates. In the second scenario an under-moderated system becomes critical as water is added before becoming subcritical as it becomes over-moderated. The models and correlations used in this paper are relatively idealised and are limited to a particular geometry and fissile solution composition. However, the results produced appear physically plausible and demonstrate that simulation of these processes are important to the long term development of transients in fissile solutions and provide a qualitative indication of the types of behaviour that may result in such situations.     

Characterization of the stress corrosion cracking behavior of thermally sensitized 20Cr-25Ni stainless steel in a simulated cooling pond environment

Niobium stabilized 20Cr-25Ni stainless steel is used for nuclear fuel cladding in the UK's fleet of advanced gas cooled reactors (AGRs). The cladding can have chromium-depleted grain boundaries as a consequence of irradiation in a reactor core, rendering a small proportion of cladding susceptible to intergranular stress corrosion cracking in cooling pond waters after removal from the reactor. In this work, thermal sensitization was used to simulate chromium depletion and the sensitized material was assessed for its susceptibility to pitting corrosion and stress corrosion cracking using slow strain rate testing (SSRT). Elevated chloride concentrations were used to accelerate corrosion initiation and propagation. In 10 ppm chloride and 80 °C, the pitting potential was at potentials between +375 mV and +400 mV (SCE). SSRT appeared to lower the pitting potential, with intergranular corrosion and intergranular stress corrosion cracks observed to nucleate at potentials of +200 mV (SCE).     

Plasma-induced grafting of acrylic acid on bentonite for the removal of U(VI) from aqueous solution

Fabrication of reusable adsorbents with satisfactory adsorption capacity and using environmentfriendly preparation processes is required for the environment-related applications. In this study,acrylic acid(AA) was grafted onto bentonite(BT) to generate an AA-graft-BT(AA-g-BT)composite using a plasma-induced grafting technique considered to be an environment-friendly method. The as-prepared composite was characterized by scanning electron microscopy, x-ray powder diffraction, thermal gravity analysis, Fourier transform infrared spectroscopy and Barrett–Emmett–Teller analysis, demonstrating the successful grafting of AA onto BT. In addition, the removal of uranium(VI)(U(VI)) from contaminated aqueous solutions was examined using the as-prepared composite. The influencing factors, including contact time,p H value, ionic strength, temperature, and initial concentration, for the removal of U(VI) were investigated by batch experiments. The experimental process fitted best with the pseudo-secondorder kinetic and the Langmuir models. Moreover, thermodynamic investigation revealed a spontaneous and endothermic process. Compared with previous adsorbents, AA-g-BT has potential practical applications in treating U(VI)-contaminated solutions.     

水溶液中环己丁酸的伽玛射线辐射降解研究

采用^60Coγ-射线辐射降解环己丁酸,通过对辐照前后化学需氧量（CODcr）与pH值变化的分析,研究了不同环己丁酸浓度、初始pH值、H202初始浓度和吸收剂量对环己丁酸的辐射降解效果的影响。结果表明：在相同剂量条件下,环己丁酸初始浓度越高,CODcr去除率越低;酸性条件更利于溶液中CODcr的去除;H202与γ-射线辐照之间具有显著的协同效应,H202初始浓度为1mmol·L-1时,其对40mg·L-1环己丁酸的辐射降解的促进效果达到最好。环己丁酸水溶液的CODcr浓度变化服从一级反应动力学方程。     

The Influence of Dissolved Hydrogen on the Corrosion of Type 304 Stainless Steels Treated with Inhibitive Chemicals in High Temperature Pure Water

In order to assess the influence of dissolved hydrogen on the intergranular stress corrosion cracking (IGSCC) characteristics of Type 304 stainless steels treated with inhibitive chemicals, electrochemical corrosion potential (ECP) measurements and slow strain rate tensile (SSRT) tests were conducted in high temperature pure water. A number of thermally sensitized specimens were prepared and then pre-oxidized in a 288°C pure water environment with the presence of 300ppb dissolved oxygen for 360h. Most of the specimens were then separately treated with various inhibitive chemicals including powdered zirconium oxide (ZrO₂), powdered titanium oxide (TiO₂), and zirconyl nitrate [ZrO(NO₃)₂] via hydrothermal deposition at 150°C. Test environments with a dissolved oxygen concentration of 300ppb and various dissolved hydrogen concentrations at 288°C were created. Test results showed that the ECPs of the treated specimens were lower than that of the untreated one no matter what the dissolved hydrogen concentration was. In addition, IGSCC was observed on all specimens (treated or untreated) in all tested environments. However, the untreated specimen exhibited lower elongation, shorter failure time, and more secondary cracks on the lateral surfaces. It was therefore suggested that inhibitive chemicals such as ZrO₂, TiO₂, and ZrO(NO₂)₂ did provide a certain degree of enhancement in improving the mechanical behavior of the treated specimens and in prolonging IGSCC initiation times.     

The effect of droplet sprinkling on the oxidation kinetics of zirconium cladding in steam

The influence of oxide layer cracking on the acceleration of Zr cladding oxidation in steam was investigated. Cracking occurs due to temperature gradients, which arise during cooling of the cladding surface by droplet jets. Experimental results on characteristics of heat removal and the temperature gradients induced are presented for different regimes of sprinkling. A model for the calculation of mechanical stresses under the experimental conditions was developed in frame of the theory of envelopes. It was shown that the stresses are sufficiently high to induce cracking of the outer oxide layer. Experimental investigations of oxidation kinetics of Zr-1%Nb cladding were carried out under the conditions of surface cooling by droplet jets. The results of these experiments confirmed that the reaction of oxidation can be strongly accelerated by sprinkling.     

The Influence of ZrO2 Treatment on the Electrochemical Behavior of Oxygen and Hydrogen on Type 304 Stainless Steels in High Temperature Water

For enhancing the effectiveness of hydrogen water chemistry (HWC) in boiling water reactors (BWRs) in the aspects of lower hydrogen consumption and of a more effective reduction in electrochemical corrosion potential (ECP), the technique of inhibitive protective coating on structural materials was brought into consideration. The application of inhibitive treatment is aimed at deterring the reduction reactions of oxidizing species occurring on metal surfaces and the oxidation reaction of metals. In the current study, electrochemical polarization analyses at 288°C were conducted to characterize the electrochemical properties of ZrO₂ treated and untreated 304 stainless steel specimens in pure water with dissolved oxygen or hydrogen. The polarization results showed that the treated specimens exhibited lower corrosion potentials, corrosion current densities, exchange current densities, and cathodic current densities than the untreated one in high temperature pure water with dissolved oxygen. For the environment with dissolved hydrogen only, reductions in anodic current density and exchange current density were observed, indicating that the ZrO₂ treatment also deterred the oxidation reaction of hydrogen. However, in comparison with the data obtained, the ZrO₂ treatment seemed to be relatively more effective in inhibiting the oxygen reduction reaction than inhibiting the hydrogen oxidation reaction. One additional beneficial outcome was that the anodic current density of the metal was also decreased, leading to a much lower overall corrosion current density of the ZrO₂ treated specimen.     

The effect of turbulence modeling on hydrogen jet dispersion inside a compartment space using the HYDRAGON code

The mitigation of hydrogen in the containment of nuclear reactor after the Loss of Coolant Accident is essential to preserve the structural reliability of the containment. This paper presents the results of the systematic work done by using the HYDRAGON code to investigate the effect of turbulence models on the concentration distribution of hydrogen and to determine the HYDRAGON code thermal-hydraulic simulation capability during a severe accident at the nuclear power plant. The HYDRAGON code is developed by the Department of Engineering Physics, Tsinghua University, which is an independent research program. The influence of various types of turbulence models, i.e. a standard k ? ? model, a re-normalized group (RNG) k ? ? model, and a realizable k ? ? model were analyzed and the simulation results were compared with the experimental data. When simulation results were compared to experimental data, it was found that, in most compartments, the standard k ? ? model generally yielded reasonable agreement with the experimental results as compared to RNG k ? ? and realizable k ? ? models; however, for probes P7 and P12, better trend was captured by RNG k ? ? and realizable k ? ? models, respectively.     

Environmentally-assisted cracking behaviour in the transition region of an Alloy182/SA 508 Cl.2 dissimilar metal weld joint in simulated boiling water reactor normal water chemistry environment

The stress corrosion cracking (SCC) and corrosion fatigue behaviour perpendicular and parallel to the fusion line in the transition region between the Alloy 182 Nickel-base weld metal and the adjacent SA 508 Cl.2 low-alloy reactor pressure vessel (RPV) steel of a simulated dissimilar metal weld joint was investigated under boiling water reactor normal water chemistry conditions. A special emphasis was placed to the question whether a fast growing interdendritic SCC crack in the highly susceptible Alloy 182 weld metal can easily cross the fusion line and significantly propagate into the adjacent low-alloy RPV steel. Cessation of interdendritic SCC crack growth was observed in high-purity or sulphate-containing oxygenated water under constant or periodical partial unloading conditions for those parts of the crack front, which reached the fusion line. In chloride containing water, on the other hand, the interdendritic SCC crack in the Alloy 182 weld metal very easily crossed the fusion line and further propagated with a very high rate as a transgranular crack into the heat-affected zone and base metal of the adjacent low-alloy steel. The observed SCC cracking behaviour at the interface correlates excellently with the field experience of such dissimilar metal weld joints, where SCC cracking was usually confined to the Alloy 182 weld metal.     

The analysis of the insertion of UO2 microspheres in the gap between pellet and clad as a new design solution to increase the burnup of the nuclear fuel

The insertion of UO₂ microspheres (eventually graphite coated) in the gap between pellet-clad is observed to decrease substantially the clad hoop plastic strain concomitantly with the elimination of the rim effect at high burnup if low enrichment is used for the microspheres. Taking into account the special features of the specialized finite element code ELFIN'90 for the behavior of fuel elements, it was possible to introduce this new type of material viewed as a granular media. The results of the new code version ELFIN'MS applications to a PHWR fuel for a power ramp irradiation history show that the hoop plastic strain is reduced by about three times in comparison to standard fuel, and that the ridge phenomenon disappears. To establish critical plastic strain limit for irradiated clad failure onset, quantitative evaluations of iodine chemisorbtion on graphite and at the surface of the irradiated zircaloy, are presented. The indications on technology procedure are also discussed. Therefore, the insertion of 2–3 layers of UO₂ microspheres of 100 μm diameter, graphite coated to retain corrosive fission products for clad and with the diameter greater than the design gap, can be considered a design solution to increase the burnup of nuclear fuel.     

The influence of defects in a plasma photonic crystal on the characteristics of microwave transmittance

Plasma photonic crystals(PPCs) have been a hot research topic in the band gap(BG) material field in recent years due to their unique advantages, such as the feasibility of changing the parameters and hence the properties of the materials with respect to traditional photonic crystals(PCs). In this paper,we focus mainly on the effects of some types of defects introduced in PPCs on the changes in BG characteristics of microwave(MW) transmittance. The research is carried out using numerical simulation with a one-dimensional finite-difference time-domain(FDTD) method, and six types of defects, including a lattice-constant defect, radii-ratio defect, additional-column defect, column-width defect, plasma-frequency defect, and electron-collision-frequency defect, are concerned. It transpires that introducing a defect in a PPC in different manners may realize the symmetric change, alternative change, shifting, generating, transforming, disappearing, and attenuating of BGs in transmittance spectra, which has great potential for the manufacture of spatiotemporal-controllable MW materials and devices with more feasible modulating functions.     

The Singular Value Decomposition as a Tool of Investigating Central MHD Instabilities in the HL-1M Tokamak

A variety of strong MHD instabilities are always resulted from MHD activity of Tokamak plasmas. Central MHD instabilities can be observed with pinhole cameras to record soft x-ray (SXR) emission from the plasma along many chords with a high temporal resolution. The investigation of MHD instabilities often necessitates an analysis on spatial-temporal signals. The method of Singular Value Decomposition (SVD) can split such signals into orthogonal spatial and temporal vectors, By this means, the repetition time and the characteristic radius of various MHD phenomena such as sawteeth and snake-like perturbation can be obtained. Moreover, the (1,1) MHD mode is analyzed in great detail by SVD and used to determine the radius of the q = 1 surface.     

低剂量X射线对小鼠睾丸生精细胞中凋亡诱导因子变化的影响

采用链霉亲和素-生物素-过氧化物酶复合物法(Strept actividin-biotin complex,SABC),观察低剂量X射线照射后小鼠睾丸各类生精细胞中(Apoptosis inducing factors,AIF)的表达变化;采用逆转录多聚酶链反应(Reverse transfer polymerase chain reaction,RT-PCR)法观察AIF的mRNA水平变化.研究低剂量X射线对小鼠睾丸生精细胞中凋亡诱导因子AIF蛋白及mRNA水平的影响.研究发现,0～0.2Gy照射后,小鼠睾丸各类生精细胞不同程度表达AIF,以精原细胞和精母细胞表达为主,精子细胞和精子则表达相对较少.AIF表达量与吸收剂量有相关性,0.075Gy照射组表达量最大,且发现AIF蛋白的表达随时间推移而增强,12h达到峰值,然后下降,但仍高于0h组.RT-PCR结果显示,低剂量照射12h后,0.1Gy剂量组AIF mRNA表达量最大.而0.075Gy照射后0-24h,其mRNA表达量逐渐增大,在24h到达峰值.所以,低剂量X线照射诱导小鼠睾丸生精细胞中AIF蛋白及mRNA表达与吸收剂量和表达时间有一定的相关性.     

雌激素拮抗剂ICI-182780对ZDY101调节 CHOm2细胞M2受体密度的影响

CHOm2细胞加雌二醇、ZDY101或等体积溶媒DMSO培养后通过3H-NMS结合反应测定M受体密度,并与同时加雌激素受体拮抗剂ICI-182780的细胞作对比.结果显示雌二醇组M受体密度为(123.7±23.9)fmol@mg-1,加ICI-182780后为(84.8±19.8)fmol@mg-1;相应的DMSO对照组为(89.6±22.9)fmol@mg-1,加ICI后为(66.9±22.5)fmol@mg-1;雌二醇组加ICI-182780后M受体密度降低的幅度远大于DMSO对照组.ZDY101组M受体密度为(147.3±36.9)fmol@mg-1,加ICI-182780后为(120.8±40.4)fmol@mg-1;相应的DMSO对照组为(95.9±24.0)fmol@mg-1,加ICI-182780后为(77.0±22.3)fmol@mg-1.表明雌激素和ZDY101都具有的提高M受体密度的功效,雌激素的药效可被ICI抑制,而ZDYl01的药效不被ICI抑制,说明ZDYl01有不同于雌激素的作用机制.