Defect evolution and atomic diffusion in U-Zr solid solutions impact advanced nuclear fuel performance, particularly irradiation stability and fission product retention. First-principles calculations are conducted to examine alloying effects on the thermodynamic stability and migration mechanisms of intrinsic and Xeincorporated defects in alpha- and delta-(U, Zr) phases. The VU and VZr vacancies are the predominant defects due to their lower formation energies. Zr alloying reduces vacancy formation energies in the U-Zr system compared to pure U, indicating enhanced defect accommodation. The predicted migration barriers for stable vacancy defects range from 1.03 to 1.14 eV in alpha-(U, Zr) phase and from 0.96 to 2.20 eV in delta-(U, Zr) alloys, higher than those in the pure alpha-U phase, suggesting that Zr alloying suppresses their diffusion under irradiation. Moreover, Xe substitutional defects (XeU and XeZr) are more energetically favorable than Xe interstitials (Xei) in alpha- and delta-(U, Zr) alloys. Zr additions stabilize the Xe substitutional and interstitial defects in the alpha-(U, Zr) phase. The migration barriers for XeU and XeZr defects are higher than those for Xei in alpha- and delta-(U, Zr) phases, indicating a preferential migration of the latter. Zr alloying hinders the diffusion of Xei in the alpha-(U, Zr), but may accelerate that of XeU in this phase. This study uncovers the effect of Zr alloying on defect behaviors in the U-Zr solid solution, contributing to the understanding of its impact on nuclear fuel expansion performance and the pore morphology formation across the alpha- and delta-(U, Zr) phases.

Radiation swelling is one of the major issues of austenitic steels used as cladding materials in liquid metal fast reactors. To extend the incubation period of swelling, cold working is commonly applied during the final processing of austenitic steel claddings. In this study, Ti-stabilized 15Cr-15Ni (15-15Ti) claddings with cold work levels ranging from 15% to 25% were fabricated, and their microstructures were examined. Helium with multiple energies was pre-implanted into the samples at room temperature prior to the heavy ion irradiation. The samples were subsequently irradiated by 85 MeV Ni8+ degraded by a tantalum foil at 580 degrees C, reaching a dose of similar to 100 dpa in the helium region. In the helium implanted and heavy-ion irradiated region, radiation swelling was observed to decrease significantly as the cold work level increases from 15% to 20%; however, the beneficial effect narrows when the cold-work increases from 20% to 25%. This saturation effect of cold work on the swelling suppression can be explained by the fact that as the level of cold work increases, twinning gradually becomes the primary deformation mechanism, but these twin boundaries contribute minimally to the radiation swelling resistance.

We investigated the irradiation damage characteristics and mechanical properties of a low-activation high-entropy alloy (LAHEA) with a body-centered cubic structure, which is reinforced with copper nanoparticles (Cu NPs). The average size of the Cu NPs was 26 nm, and they were uniformly dispersed within the BCC matrix, exhibiting perfect coherence with the matrix. The addition of Cu enhanced the yield strength of the alloy from 767 to 1255 MPa and increased the elongation to 15.4%, which is attributed to the pinning effect of the Cu particles on dislocations and their high deformability. After high-dose Ni-ion irradiation at 580 degrees C, selected to align with BCC alloy swelling behavior, the material demonstrated exceptional radiation resistance characterized by the complete suppression of void formation. Cross-sectional microstructural analysis revealed that irradiationinduced Ti-rich semi-coherent precipitates contributed to hardening, while coherent Fe/Mn-rich clusters acted as efficient point-defect recombination centers. These findings indicate that the low-activation HEA has substantial potential for nuclear applications.

The topological insulator MnSb2Te4 shows promising potential in thermoelectric applications due to its intrinsically low lattice thermal conductivity. However, its thermoelectric performance is limited by the high carrier concentration, of which the origin is still unclear. In this work, the carrier concentration is successfully tuned from 2.24 × 1021 cm-3 to as low as 9.1 × 1019 cm-3. Transmission electron microscopy and positron annihilation measurements suggest that large amounts of Mn vacancies exist in the septuple layer of MnSb2Te4, which are responsible for the high carrier concentration. The Mn vacancies are suppressed by the excess Mn element and AgSbTe2 alloying, which not only reduces the carrier concentration but also weakens the carrier scattering and thus improves the mobility. The decrease in carrier concentration also leads to reduced electronic thermal conductivity. The excess Mn atoms introduce a strain field in the Mn layer, which enhances phonon scattering. Furthermore, the substitution of Ag for Mn causes lattice softening by weakening the chemical bonds in MnSb2Te4, which leads to reduced phonon velocity and, therefore, further reduction in lattice thermal conductivity. As a result, an extremely low lattice thermal conductivity of 0.44 W m-1 K-1 was obtained at 300 K and it further decreased to 0.17 W m-1 K-1 at 798 K. Finally, a record zT value of 1.53 at 798 K was achieved in Mn1.06Sb2Te4(AgSbTe2)0.04, and the optimal carrier concentration is about 2 × 1020 cm-3.

Molybdenum-rhenium (Mo-Re) alloys are regarded as important candidate structural materials for nuclear reactors. Apart from the known χ phase, limited research has been conducted on other precipitate phases, particularly hcp-Re. In this study, the Mo-42Re (wt. %) alloy was irradiated using 20 MeV Ni+3 ions at 853 K, reaching a maximum dose of 140 dpa. Five indirect evidences supported that there is a kind of phase different from the χ phase and that it is probable to be hcp-Re. Distinct radiation-induced precipitation (RIP) phenomenon is observed, with the χ phase commonly appearing as a radiation-induced precipitate and two shapes of probable hcp-Re. The two shapes of hcp-Re are the needle-like hcp-Re formed during growth and the small, near-equiaxed hcp-Re formed during nucleation. Explaining the different shapes of hcp-Re from the perspectives of nucleation and growth may help clarify past debates on the existence and morphology of hcp-Re.

This study examines the irradiation resistance of a novel Ti8V22.5Cr22.5Mn22.5Fe22.5Si2 high-entropy alloy (HEA) through techniques such as scanning/transmission electron microscopy, positron annihilation spectroscopy, and grazing incidence X-ray diffraction. The results highlight an unusual lattice contraction upon irradiation, diverging from typical responses of traditional alloys, with no evidence of irradiation-induced precipitation. Under high-dose irradiation (similar to 188 dpa), the HEA displayed no discernible void swelling, potentially due to abundant precipitate interfaces, high equilibrium vacancy concentration, and the intrinsic properties of HEA. The HEA, exhibiting smaller dislocation loops (similar to 3.2 nm) and a lower irradiation hardening rate (similar to 3.3 %) compared to conventional alloys, demonstrates significant promise as a material for future-generation core components.

To ensure the safe operation of pressurized water reactors, the real-time and high-sensitive monitoring of Li and Zn in primary cooling water is required. Laser-induced breakdown spectroscopy (LIBS) is a real-time analytical method with great application potential for elemental monitoring in primary cooling water. However, when LIBS directly detects liquids, plasma quenching will reduce the detection sensitivity. In this work, capillary effect- enhanced LIBS (CE-LIBS) was proposed to improve the detection sensitivity of elements in aqueous solutions. Titanium foam substrates were used to enrich the solutes in the solutions. The signal enhancement mechanisms of the method were analyzed. The results showed that the solutes were enriched on the surface of the titanium foam substrate due to the capillary effect. The excitation temperature and electron density of the laser-induced plasma were both increased by the titanium foam substrate, thus increasing the plasma emission intensity. The limits of detection of Li and Zn were 0.41 and 3.83 ng/mL by using CE-LIBS, which can fully meet the requirements of Li and Zn monitoring in primary cooling water. The practicability of the method was demonstrated by analyzing simulated primary cooling water samples, and the recovery values of Li and Zn were in the range of 92-105 % and 96-102 %, respectively. The CE-LIBS does not require additional treatment of the substrate, and the detection process is simple and fast. Results indicated that the CE-LIBS method has broad application prospects in the real-time and high-sensitivity detection of elements in aqueous samples.

In the present work, we design a laminated composite composed of molybdenum–rhenium alloy and silicon carbide ceramics for use in space reactors as a candidate structural material with neutron spectral shift properties. The influence of the internal microstructure on the mechanical properties is investigated by finite element simulation based on scale separation. The results of the study showed that the incorporation of gradient transition layers between the metallic and ceramic phases effectively mitigates thermally induced local stresses arising from mismatches in coefficients of thermal expansion. By optimizing the composition of the gradient transition layers, the stress distribution within the composite under operating conditions has been adjusted. As a result, the stress experienced by the alloy phase is significantly reduced, potentially extending the high-temperature creep rupture life.

Gallium oxide,a wide band gap semiconductor,is a focus material in the semiconductor field at present.Many mature processes have been developed for n-type doping of gallium oxide.However,the conventional doping process has not achieved its p-type doping on bulk crystals,which hinders its application.Proton irradiation transmutation doping is considered to be a more likely p-type doping method than thermal diffusion method and ion implantation method.Proton irradiation transmutation doping is realized by using the transmutation products produced by the nuclear reaction between high-energy protons and target materials.Proton irradiation transmutation doping can put doping atoms at lattice sites.It can also produce more uniform impurity distribution in target materials.What is more,proton irradiation transmutation can produce many elements in gallium oxide crystals.The co-doping effect of many different elements can not be considered as the superposition of single doping effect.Currently,it is considered that two element co-doping has the effect of reducing ionization energy.Therefore,it is hopeful to realize p-type doping of gallium oxide by Coulomb coupling effect of many doping elements imported by proton irradiation transmutation.In this paper,the transmutation doping of gallium oxide irradiated by 100 MeV protons was simulated and analyzed by using the Monte Carlo software FLUKA of nuclear reaction.The simulation conditions were set according to the beam output capacity of the high-current proton cyclotron of China Institute of Atomic Energy.In the analysis,there are 17 kinds of elements and about 80 kinds of nuclides that have significant influence on gallium oxide doping.Over half of nuclides are radionuclides.Simulation calculation was mainly about the activity and transmutation element concentration of gallium oxide after proton irradiation.The results show that the activation activity decreases by about four orders of magnitude after 100 cooling days,and the element concentration of transmutation products tends to be stable.Within the depth range of 1.50 cm of gallium oxide,the specific activity of the target material does not change obviously with the depth.The analysis of element concentrations of transmutation products with different doping types shows that proton irradiation transmutation can generate net p-type doping.The net p-type doping concentration is different at different depths of the target material.It is the largest at the depth of 0.60-0.90 cm,which can reach 4.26×1014 cm-3 per 1016 cm-2 proton fluence.Compared with the doping of 40 MeV proton irradiation and fast neutron irradiation,100 MeV proton irradiation transmutation doping efficiency is higher.

Abstract Ion irradiation combined with nanoindentation has been widely used to evaluate the irradiation-hardening effect of materials. Depth-dependent hardening resulting from the non-flat damage profile in heavy-ion irradiation, coupled with the indentation size effect (ISE) in nanoindentations, would further increase the complexity of the extraction of irradiation hardening. In this paper, a simple and reliable approach to decouple the indentation size effect from nanoindentation hardness was proposed based on the modified Nix-Gao model with an extended plastic zone. A hardness dependency was introduced in the indentation characteristic length as well as in the plastic zone size, so that their values will smoothly alter with increasing indentation depths and naturally reduce to the values of the unirradiated material when the indentation depth is well beyond the irradiation zone. The indentation size effect in the measured nano-hardness of ion-irradiated samples can be effectively separated out using the proposed method.

Exposure of metals to neutron irradiation results in an increase in the yield strength and a significant loss of ductility. Irradiation hardening is also closely related to the fracture toughness temperature shift or the ductile-to-brittle transition temperature (DBTT) shift in alloys with a body-centered cubic (bcc) crystal structure. Ion irradiation is an indispensable tool in the study of the radiation effects of materials for nuclear energy systems. Due to the shallow damage depth in ion-irradiated materials, the nanoindentation test is the most commonly used method for characterizing the changes in mechanical properties after ion irradiation. Issues that affect the analysis of irradiation hardening may arise due to changes in the surface morphology and mechanical properties, as well as the inherent complexities in nanoscale indentation. These issues, including changes in surface roughness, carbon contamination, the pile-up effect, and the indentation size effect, with corresponding measures, were reviewed. Modeling using the crystal plasticity finite element method of the nanoindentation of ion-irradiated materials was also reviewed. The challenges in extending the nanoindentation test to high temperatures and to multiscale simulation were addressed.

Tungsten-nickel-iron (W-Ni-Fe) alloys, commonly known as W heavy alloys (WHAs), exhibit enhanced ductility, thermal conductivity, and mechanical attributes. These properties render WHAs highly suitable as plasma-facing materials in lieu of pure W. This investigation examines the irradiation resistance of two WHAs—97W-2Ni-1Fe and 90W-7Ni-3Fe—by subjecting them to He ion irradiation at doses reaching 5 × 1017 ions/cm2. The study establishes that low-dose irradiation (1 × 1017 ions/cm2) inflicted negligible surface damage on both WHA compositions. Nonetheless, increasing the radiation dose to 5 × 1017 ions/cm2 led to observable surface impairments, albeit at a reduced magnitude when compared to pure W. An array of analytical methods was employed to characterize irradiation-induced microstructures and void swelling, including positron annihilation spectroscopy, thermal desorption spectroscopy, and transmission electron microscopy. These analyses revealed that low-dose irradiated WHAs predominantly generated vacancy-type defects. Moreover, these defects evolved into HemVn and HemVn-NiFe complexes as the irradiation dose increased. Concurrently, He bubble density escalated with rising irradiation dosage. When subjected to an irradiation dose of 1 × 1017 ions/cm2, both alloys manifested desorption levels approximately 6.5 times greater than that observed in pure W. The findings of this investigation offer valuable insights to the understanding of WHA irradiation behavior in nuclear materials.

The swelling behavior of titanium-modified austenitic stainless steel 15-15Ti was investigated by pre-implantation of He at room temperature followed by Ni irradiation at 580 °C to peak doses of 120, 240 and 400 dpa. Relatively smaller cavities were observed in the zone of helium implantation while large cavities appeared in the region near the damage peak. A correction formula of the dpa curve was proposed and applied for samples with large swelling. It is found that the steady-state swelling rate of 15-15Ti keeps at ~1% /dpa even to high doses. By comparing the swelling data of the helium-implanted and helium-free regions at same doses, 70 dpa and 122 dpa, the suppression of excessive helium on swelling can be deduced at such doses.

this paper, we apply Bayesian inference to constrain the nuclear equation of state parameters by using properties of neutron stars, including the maximum neutron star mass, radius, tidal deformability at 1.4 times the solar mass, and speed sound. When the polytrope EOS parameter y is fixed at 2.9 and above four astronomical observations are simultaneously used, the mean values and uncertainties of the nuclear matter parameters derived from standard Skyrme interactions are follows: incompressibility K 0 = 243.4 +/- 22.0 MeV, symmetry energy coefficient S 0 = 29.3 +/- 2.9 MeV, the slope of symmetry energy L = 74.4 +/- 14.8 MeV, the isoscalar effective mass m & lowast;s/m = 0.79 +/- 0.13, and a quantity related to effective mass splitting fI = 0.08 +/- 0.30 (when fI > 0, this implies that the effective mass of neutrons is less than that of protons). When considering the uncertainty of y in the range of 2.45-2.9, we found that K 0 increased by 11%, S 0 decreased by 2%, decreased by 20%, m & lowast;s/m decreased by 4%, and the averaged value of fI reduced by 88%. Particularly, if constraints are based solely on neutron star masses less than 2.05 M circle dot , the preferred effective Skyrme interactions exhibit a neutron effective mass greater than the proton effective mass, i.e., fI < 0. The inverse sign of the constrained fI implies that reducing the uncertainties of the effective Skyrme interaction parameters needs combination analysis with heavy-ion collisions in future studies.

The titanium-stabilized austenitic stainless steel Fe-15Cr-15Ni, which shows enhanced resistance to irradiation swelling compared with more traditional 316Ti, has been selected as a core material for fast reactors. Data on the evolution of irradiation swelling in 15-15Ti steels at very high doses, which cannot be easily achieved by neutron irradiation, are still lacking. In this paper, the swelling behavior of the titanium-modified austenitic stainless steel 15-15Ti was investigated by pre-implantation of He at room temperature followed by Ni-ion irradiation at 580 °C to peak doses of 120, 240 and 400 dpa. Relatively small cavities were observed in the zone of helium implantation, while large cavities appeared in the region near the damage peak. A correction formula for the dpa curve was proposed and applied to samples with large swelling. It was found that the steady-state swelling rate of 15-15Ti remains at ~1%/dpa even at high doses. By comparing the swelling data of the helium-implanted and helium-free regions at same doses, 70 dpa and 122 dpa, the suppression of swelling by excessive helium can be deduced at such doses.

The accuracy of activity determination for activated nuclide 56Mn is the key to the manganese bath method applying to the characterization of radionuclide neutron source. As an alternative to the 4π(Č)-γ method, TDCR-Čerenkov method could also be applied to the measurement of 56Mn in the manganese bath device, if the existing calculation model is extended. There are two difficulties when the existing TDCR-Čerenkov method is applied to the activity determination of 56Mn. One is that the efficiency computation of gamma transitions, and the other is the interference contributed by Čerenkov photons emitted in the photomultiplier windows induced by Compton scattering. In this study, the above two difficulties are solved by extending the calculation model. For efficiency computation, the decay scheme of 56Mn is taken into account in the calculation of efficiency. Among them, the efficiency of gamma transition is calculated from the simulated secondary electronic spectra. In addition, Čerenkov photons emitted in photomultiplier windows are corrected by additional light proof experiment and improved calculation model. The results derived from this extended method are in good agreement with other standardization technique.

Background55Fe is a low-energy radionuclide that is difficult to measure and decays to a ground state of 55Mn through pure electron capture (EC), accompanied by the emission of Auger electrons and low-energy X-ray. As iron is the main component of nuclear reactor building materials, significant amounts of 55Fe have been produced in nuclear reactors and other neutron-producing nuclear facilities.PurposeThis study aims to develop an 55Fe nuclide standard through the absolute measurement of 55Fe activity and provides activity traceability services for 55Fe measuring instruments to ensure the accuracy and consistency of the measurement results of calibration instruments.MethodsThe liquid scintillation triple-to-double coincidence ratio (TDCR) method was applied to determining the activity of 55Fe. First, based on nuclear and atomic data of 55Fe, the electron deposition spectrum of 55Fe in a scintillator was calculated using a random atomic rearrangement model. Second, the counting efficiency of single-energy electron was computed based on the free parameter model. The total efficiency curve of 55Fe was then obtained by summing the efficiency of all deposited electrons. Finally, the experimental counting efficiency was derived by measuring the TDCR value and combining it with the total efficiency curve to realize an absolute measurement of 55Fe activity.ResultsThe experimental results show that correction factors for the asymmetric effect of photomultiplier tube (PMT) quantum efficiency obtained on test samples are between 1.001 and 1.005. The measured specific activity of 55Fe is 94.15 kBq∙g-1 with a relative standard uncertainty of 0.45%. Experimental efficiency is better than 63% for double coincidence logic sum of liquid scintillation counter.ConclusionsThis study demonstrates that low relative standard uncertainty of 55Fe activity could be achieved using the liquid scintillation TDCR method with high detection efficiency, and more consistent measurement results can be obtained after applying the asymmetry correction of PMT quantum efficiency.

A new 4πβ(LS)-γ digital coincidence counting (DCC) system has been developed at NIM. The system equipped with a triple-to-double coincidence ratio (TDCR) counter in the β-channel and a NaI(Tl) scintillation detector in the γ-channel. A dedicated DCC software was designed for off-line implementation of 4πβ(LS)-γ coincidence counting method. The software consists of three modules: software-based circuits module, dead-time and resolving-time correction module and efficiency extrapolation module, respectively. The performance of the newly developed 4πβ(LS)-γ DCC system was demonstrated by a comparison measurement of Co-60 solution with the conventional 4πβ(PC)-γ DCC system.

Titanium-modified austenitic stainless steels (15-15TiSS) are currently used as the fuel cladding material of fast reactors, which are subject to higher radiation damage during their application. In this work, the radiation-induced swelling of 15-15TiSS under a fast reactor neutron and heavy ion irradiation conditions was studied by the rate theory (RT). The simulated swelling properties of 15-15TiSS under fast neutron conditions were calculated initially. The swelling peak, swelling rates, and swelling-related microstructural properties are consistent with the neutron irradiation results, indicating that the selected RT model and material parameters are reasonable. Then, the swelling properties of 15-15TiSS under various damage rates were predicted by changing the radiation damage rates from 1 × 10−6 to 1 × 10−3 dpa/s. It shows that swelling peaks are strongly dependent on temperature and the swelling peaks shift ∼50 °C toward the higher temperature with each order of magnitude increase of defects generation rate. The swelling rates and swelling-related defect evolution at 1 × 10−3 dpa/s (with a swelling peak temperature of 590 °C) are consistent with that under neutron irradiation with 1 × 10−6 dpa/s (with a swelling peak temperature of 460 °C). At length, the RT-predicted heavy ions irradiation results were verified by the previous positron annihilation lifetime spectroscopy results of ions irradiated 15-15TiSS. It indicates that heavy ion irradiation can be used to study the radiation effect of materials under neutron irradiation and should be a feasible technique used in the further screening of radiation-resistant materials.

Designing high-performance radiation-tolerant materials and understanding the atomistic mechanism of radiation resistance are important topics in nuclear energy structural materials research. In this study, we investigated the atomistic mechanism of the formation of rod-like precipitates in helium-irradiated ferritic-martensitic steels (F-M steels) by positron annihilation spectroscopy (PAS) and transmission electron microscopy with energy dispersive X-ray spectroscopy (TEM/EDX). The results indicated that vacancies tended to accumulate near dislocation lines to form complexes in the reduced activation ferritic-martensitic (RAFM) steel. Moreover, Fe and Cr atoms diffused toward these complexes and eventually depleted therein, which was not conducive to the formation of rod-like precipitates. Conversely, impurity atoms such as C atoms were found to segregate near dislocations in the Y-bearing oxide dispersion strengthened (Y-ODS) steel. When Fe and Cr diffused toward dislocations, they exchanged positions with C atoms until Fe and Cr exceeded their saturation solubilities and precipitated on the glide plane. We also analyzed the distribution of vacancy defects and bubbles/voids in the four irradiated materials and discussed the radiation resistance mechanism of the precipitates. The results of this study are significant in demonstrating a microscopic mechanism of radiation-induced precipitates to swelling resistance in materials.