Mechanical properties of 9Cr–1W reduced activation ferritic martensitic steel weldment prepared by electron beam welding process

Microstructure and mechanical properties of the weldments prepared from 9Cr–1W reduced activation ferritic martensitic (RAFM) steel using electron beam welding (EBW) process were studied. Microstructure consists of tempered lath martensite where precipitates decorating the boundaries in post weld heat treated (PWHT) condition. Lath and precipitate sizes were found to be finer in the weld metal than in base metal. Accordingly, hardness of the weld metal was found to be higher than the base metal. Tensile strength of the cross weldment specimen was 684 MPa, which was comparable with the base metal tensile strength of 670 MPa. On the other hand, DBTT of 9Cr–1W weld metal in as-welded condition is similar to that reported for TIG weld metal in PWHT condition.     

186W(d,p)187W和186W(d,2n)186Re反应激发函数评价及厚靶产额计算

考虑特征γ射线分支比、衰变常量和标准截面等修正,对氘引起的核反应¹⁸⁶W(d,p)¹⁸⁷W和¹⁸⁶W(d,2n)¹⁸⁶Re的激发函数进行了研究。收集并分析了这些反应激发函数的实验测量数据,应用数学方法对分析处理后的实验数据进行了拟合。同时,采用TALYS程序对这些激发函数进行了理论计算。经过综合评价,给出了50 MeV以下¹⁸⁶W(d,p)¹⁸⁷W和¹⁸⁶W(d,2n)¹⁸⁶Re反应激发函数的推荐值,利用得到的¹⁸⁶W(d,2n)¹⁸⁶Re激发函数推荐值计算了医用放射性核素¹⁸⁶Re的厚靶产额。     

Desorption of gold nanoclusters (2–150 nm) by 1 GeV Pb ions

Nanodispersed targets of gold (grains sized at 2–150 nm) were irradiated with 956 MeV ions of Pb⁵⁴⁺ ((dE/dx)_e in gold 87 keV/nm). Ejected gold was gathered on collectors. Desorbed nanoclusters of gold were detected by means of TEM while the total matter transfer was measured by neutron activation analysis. For all the targets a part of ejected gold presents nanoclusters in the same size range as that of the grains on the corresponding targets. Desorption of nanoclusters with the size up to 90 nm was observed for the first time for atomic primary ions in the electronic stopping regime. The yield of the desorbed nanoclusters decreases from 22 to 1.4 cluster/ion with increasing the mean grain size from 6 to 30 nm. The total matter transfer measured for the target with the grain size 6–10 nm has a great value – 5 × 10⁵ at./ion. Results are discussed.     

Spectroscopic and microscopic study of the corrosion of iron–silicon steel by lead–bismuth eutectic (LBE) at elevated temperatures

The performance of iron–silica alloys with different silicon composition was evaluated after exposure to an isothermal bath of lead–bismuth eutectic (LBE). Four alloys were evaluated: pure iron, Fe–1.24%Si, Fe–2.55%Si and Fe–3.82%Si. The samples were exposed to LBE in a dynamic corrosion cell for periods from 700 to 1000 h at a temperature of 550 °C. After exposure, the thickness and composition of the oxide layer were examined using optical microscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS), including sputter depth profiling. Particular attention was paid to the role, spatial distribution, and chemical speciation of silicon. Low-binding-energy silicon (probably silicates or ) was found in the oxide; while elemental silicon (Si) was found in the metal as expected, and silica (SiO₂) was found at the bottom of the oxide layer, consistent with the formation of a layer between the oxide and the metal. Alloys with low concentrations of Si contained only silicate in the oxide. Alloys with higher concentrations of Si contained a layer of silica at the boundary between the oxide and the bulk metal. All of the alloys examined showed signs of oxide failure. This study has implications for the role of silicon in the stability of the oxide layer in the corrosion of steel by LBE.     

Microstructure alterations in the base material, heat affected zone and weld metal of a 440-VVER-reactor pressure vessel caused by high fluence irradiation during long term operation; material: 15 Ch2MFA ≈0.15 C–2.5 Cr–0.7 Mo–0.3 V

Within the scope of the EC research project Tacis ’91 (‘RPV-Embrittlement’), trepans were taken from the highly irradiated circumferential RPV-weld of the Novovoronesh power plant unit-2 of the type VVER-440/230. The cumulated fast fluence level in this position reaches up to 6.5×10¹⁹/cm² (E>0.5 MeV). In a joint research work, the mechanical properties, the chemical composition, and the microstructure of the base material, the heat affected zone (HAZ), and the weld metal have been investigated in order to study the influence of irradiation, and of post irradiation heat treatment (475°C, 560°C) on the properties. The examination of the microstructure performed by analytical transmission electron microscopy (200 kV) shows the existence of dislocation loops (‘black dots’), irradiation induced precipitates, and segregation of copper in the carbides. These changes in microstructure, which are due to service affection (neutron irradiation, temperature) have occurred more pronounced in the weld metal and the HAZ than in the base material.     

On the round table discussion on reactor power margins published in Nuclear Engineering and Design 163 (1–2) 1996

Some comments concerning the critical heat flux (CHF) correlations, the usage of the direct substitution versus the heat balance methods for correlation evaluation and the definition of CHF margins considered in the round table discussion on reactor power margins are presented.     

双束同时辐照低活性Fe-Cr-Mn(W、V)合金微观组织损伤的影响

研究了时效热处理低活性Fe Cr Mn(W、V)钢双束同时辐照损伤行为 ,结果表明 :92 3K/ 3 0 0 0h时效合金 ,经单独电子辐照 (1 0a- 1)出现低密度空洞 ,而经双束同时辐照的时效合金 ,在辐照初期就形成间隙型位错环和微小空洞。与无时效合金相比 ,随时效温度增加 ,空洞尺寸、空洞密度和空洞肿胀量增大。随时效温度的提高碳化物析出数量增多 ,奥氏体中合金元素Cr、Mn、W、V降低 ,He的存在有效地促进空洞肿胀量增大。     

Energy levels,wavelengths, and transition rates of multipole transitions (E1, E2, M1, M2) in Au and Au ions

The fully relativistic configuration interaction method of the FAC code is used to calculate atomic data for multipole transitions in Mg-like Au (Au⁶⁷⁺) and Al-like Au (Au⁶⁶⁺) ions. Generated atomic data are important in the modeling of M-shell spectra for heavy Au ions and Au plasma diagnostics. Energy levels, oscillator strengths and transition rates are calculated for electric-dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2) for transitions between excited and ground states 3l−nl^′$3l-n{l}^{\prime }$, such that n=4,5,6,7$n=4,5,6,7$. The local central potential is derived using the Dirac–Fock–Slater method. Correlation effects to all orders are considered by the configuration interaction expansion. All relativistic effects are included in the calculations. Calculated energy levels are compared against published values that were calculated using the multi-reference many body perturbation theory, which includes higher order QED effects. Favorable agreement was observed, with less than 0.15% difference.     

Electrical conductivity and non-stoichiometry in the (U,Gd)O2±x system

The isothermal electrical conductivity and oxygen potential of the (U,Gd)O_2±x solid solution were measured in various oxygen partial pressure regions at 1200 °C and 1300 °C. The electrical conductivity gradually decreased with decreasing oxygen partial pressure even in the hypo-stoichiometric region. These findings were in contrast to the implication of a hypo-stoichiometry where the electrical conductivity is increased through the formation of oxygen vacancies. The (U_1−yGd_y)O_2−y/2 was defined as a new stoichiometric composition to determine the relationship between the deviation of the oxygen composition from stoichiometry and oxygen partial pressure. The dependence of the new oxygen deviation, z in (U_1−yGd_y)O_2−y/2+z, on the oxygen partial pressure corresponds to the dependence of the electrical conductivity, and thus a consistent defect structure model can be deduced from both the dependence curves. It suggests that the defect type is oxygen interstitial even below the oxygen composition of 2.     

Relativistic many-body calculations of multipole (E1, M1, E2, M2, E3, and M3) transition wavelengths and rates between 3l4l′ excited and ground states in nickel-like ions

Wavelengths, transition rates, and line strengths are calculated for the 76 possible multipole (E1, M1, E2, M2, E3, and M3) transitions between the excited 3s²3p⁶3d⁹4l, 3s²3p⁵3d¹⁰4l, and 3s3p⁶3d¹⁰4l and the ground 3s²3p⁶3d¹⁰ states in Ni-like ions with the nuclear charges ranging from Z = 30 to 100. The relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate energies and transition rates for multipole transitions in hole-particle systems. This method is based on relativistic many-body perturbation theory, agrees with MCDF calculations in lowest-order, includes all second-order correlation corrections, and includes corrections from negative energy states. The calculations start from a 1s²2s²2p⁶3s²3p⁶3d¹⁰ Dirac-Fock potential. First-order perturbation theory is used to obtain intermediate-coupling coefficients, and the second-order RMBPT is used to determine the matrix elements. The contributions from negative-energy states are included in the second-order E1, M1, E2, M2, E3, and M3 matrix elements. The resulting transition energies and transition rates are compared with experimental values and with results from other recent calculations. As a result, we present wavelengths and transition rates data for the selected transitions that include the 76 possible multipole (E1, M1, E2, M2, E3, and M3) transitions between the excited 3s²3p⁶3d⁹4l, 3s²3p⁵3d¹⁰4l, and 3s3p⁶3d¹⁰4l states and the ground 3s²3p⁶3d¹⁰ state in Ni-like ions. Trends of the line strengths for the 76 multipole transitions and oscillator strengths for the 13 E1 transitions as function of Z are illustrated graphically. The Z-dependence of the energy splitting for all triplet terms of the 3s²3p⁶3d⁹4l, 3s²3p⁵3d¹⁰4l, and 3s3p⁶3d¹⁰4l configurations are shown in the range of Z = 30-100.     

Detailed analysis of (n,p) and (n,α) cross sections in the EAF-2007 and TALYS-generated libraries

Large cross section libraries, such as EAF-2007 used for activation calculations, need to be validated. A traditional approach employs simple systematic formulae based on experimental data and derived at energies such as 14.5 MeV. Such systematics are also used for renormalization of cross sections during library preparation. This approach is gradually being replaced by using results of sophisticated nuclear model calculations. As the energy range of EAF libraries has expanded from 20 to 60 MeV an additional approach is required and the method of ‘statistical analysis of cross sections’ (SACS) has proved to be useful. SACS analyses are carried out for the important charged particle reactions (n,p) and (n,α) in the EAF-2007 and TALYS-6 libraries. TALYS-6 is a calculational library generated by the TALYS model code Version 0.72. SACS considers various reaction statistics such as σ_max, E_max and Δ_1/2 and plots scatter plots against a parameter such as the asymmetry (s). Trend lines using simple algebraic formulae can be fitted to the data and points discrepant from the trends correspond to reactions that require improvement. A new observation is a ‘step’ in the Δ_1/2(s) plot for (n,p) reactions and this has been interpreted as due to competition between (n,p) and (n,n′p) reaction channels. Equations for the various trend curves for EAF-2007 are given.     

Ratio tests of dosimetry cross-sections for Nb(n,2n)Nb and Au(n,2n)Au to Al(n,α)Na reactions

Cross-section ratios of reaction ⁹³Nb(n,2n)^92mNb and ¹⁹⁷Au(n,2n)¹⁹⁶Au to the standard reaction ²⁷Al(n,α)²⁴Na have been measured in order to test the recently compiled dosimetry files: JENDL Dosimetry File and International Reactor Dosimetry File 1990 (IRDF-90). The experimental results for both reactions were consistent with the calculated ones based on IRDF-90 except for the ⁹³Nb(n,2n)^92mNb above 19 MeV.Both reactions, especially ⁹³Nb(n,2n)^92mNb, were recommended as new neutron monitors above 12 MeV because of their favorable characteristics from the decay-property and cross-section viewpoints.     

Energy window effect in chemisorption of C36 on diamond (0 0 1)-(2×1) surface

In this paper, the collision of a C₃₆, with D_6h symmetry, on diamond (0 0 1)-(2×1) surface was investigated using molecular dynamics (MD) simulation based on the semi-empirical Brenner potential. The incident kinetic energy of the C₃₆ ranges from 20 to 150 eV per cluster. The collision dynamics was investigated as a function of impact energy E_in. The C₃₆ cluster was first impacted towards the center of two dimers with a fixed orientation. It was found that when E_in was lower than 30 eV, C₃₆ bounces off the surface without breaking up. Increasing E_in to 30–45 eV, bonds were formed between C₃₆ and surface dimer atoms, and the adsorbed C₃₆ retained its original free-cluster structure. Around 50–60 eV, the C₃₆ rebounded from the surface with cage defects. Above 70 eV, fragmentation both in the cluster and on the surface was observed. Our simulation supported the experimental findings that during low-energy cluster beam deposition small fullerenes could keep their original structure after adsorption (i.e. the memory effect), if E_in is within a certain range. Furthermore, we found that the energy threshold for chemisorption is sensitive to the orientation of the incident C₃₆ and its impact position on the asymmetric surface.     

A computational study of bond-breaking process of Cu–Si bond during ion sputtering of a Cu/Si(1 1 1) surface, based on molecular orbital theory

A theoretical approach based on molecular orbital theory has been provided. By applying this theory to a bond-breaking process, the ionization probability of Cu adsobates sputtered from a “5×5”-Cu/Si(1 1 1) surface has been studied. Three important aspects have been confirmed: (1) importance of a long range electrostatic potential such as the image potential, (2) importance of the coulomb repulsive potential between the Cu 4s spin-up and spin-down electron, and finally (3) acceleration and deceleration effects depending on charge state, which is a result of the interplay of the molecular bonding interaction and the long range electrostatic interaction. The measurements of ionization probability will provide us more information of the adiabatic potential curves of the reactants from the surfaces.     

J-R fracture properties of SA508-1a ferritic steels and SA312-TP347 austenitic steels for pressurized water reactor’s (PWR) primary coolant piping

J-R fracture resistance of SA508-1a and SA312-TP347 steels, which are both rather peculiar as PWR primary coolant piping materials, were evaluated for application of leak-before-break methodology to the design basis of nuclear power plant piping. Archive materials from various heats of both steel pipes showed apparent heat-to-heat variations in ductile fracture resistance at the operating temperature 316°C. The SA508-1a ferritic steels showed relatively good J-R curve properties although they varied with the microstructures depending on the manufacturing process and chemical compositions. On the other hand, ductile crack growth resistance of SA312-TP347 austenitic stainless steel was unexpectedly poor when carbon content is moderately high. It was found that coarse niobium carbides deteriorated the ductile fracture resistance, so that more rigorous specification is needed in carbon and niobium contents to improve fracture properties of Type 347 stainless steels.     

Computer simulation of sputtering at the low index (1 0 0), (1 1 0) and (1 1 1) surfaces of Ni3Al in a STEM

The present study is relevant to the preferential Al sputtering and/or enhancement of the Ni/Al ratio in Ni₃Al observed by the scanning transmission electron microscopy fitted with a field emission gun (FEG STEM). Atomic recoil events at the low index (1 0 0), (1 1 0) and (1 1 1) surfaces of Ni₃Al through elastic collisions between electrons and atoms are simulated using molecular dynamics (MD) methods. The threshold energy for sputtering, E_sp, and adatom creation, E_ad, are determined as a function of recoil direction. Based on the MD determined E_sp, the sputtering cross-sections for Ni and Al atoms in these surfaces are calculated with the previous proposed model. It is found that the sputtering cross-section for Al atoms is about 7-8 times higher than that for Ni, indicating the preferential sputtering of Al in Ni₃Al, in good agreement with experiments. It is also found that the sputtering cross-sections for Ni atoms are almost the same in these three surfaces, suggesting that they are independent of surface orientation. Thus, the sputtering process is almost independent of the surface orientation in Ni₃Al, as it is controlled by the sputtering of Ni atoms with a lower sputtering rate.     

Measurements and model calculations of activation cross sections for 232Th(n,2n)231Th reaction between 13.57 and 14.83 MeV neutrons

In this study, activation cross sections were measured for the reaction of ²³²Th(n,2n)²³¹Th (T_1/2 = 25.5 h) by using neutron activation technique at six different neutron energies from 13.57 and 14.83 MeV. Neutrons were produced via the ³H(²H,n)⁴He reaction using SAMES T-400 neutron generator. Irradiated and activated high purity Thorium foils were measured by a high-resolution γ-ray spectrometer with a high-purity Germanium (HpGe) detector. In cross section measurements, the corrections were made for the effects of γ-ray self-absorption in the foils, dead-time, coincidence summing, fluctuation of neutron flux, low energy neutrons. For this reaction, statistical model calculation, which the pre-equilibrium emission effects were taken into consideration, were also performed between 13.57 and 14.83 MeV energy range. The cross sections were compared with previous works in literature, with model calculation results, and with evaluation data bases (ENDF/B-VII, ENDF/B-VI, JEFF-3.1, JENDL-4.0, JENDL-3.3, and ROSFOND-2010).