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In this study, BSi cluster ions of 77 keV and B monomer ions of 22 keV were respectively implanted into silicon wafers at room temperature and geometrically tilted. Rapid thermal annealing of the as-implanted specimens at 1050 °C for 25 s was also employed. The results revealed that all the as-implanted and as-annealed range parameters (Rp, ΔRp, γ, β and ΔRt) of the BSi cluster ion implantation are smaller than those of the B monomer ion implantation. The as-annealed range parameters are larger than the as-implanted ones for both the BSi cluster ion and the B monomer ion implantations mainly due to radiation enhanced diffusion (RED) effects. RED effects also tend to drive boron atoms out-diffusion towards the specimen surface. However, the SiO2 layer at the surface acts as a diffusion barrier by which it traps boron atoms nearby. The existence of larger amounts of defects explains the presence of a more pronounced accumulation of out-diffused boron atoms in the as-annealed boron depth profile of the BSi cluster ion implantation compared to that of the B monomer ion implantation. [Copyright &y& Elsevier]

Neutron transmutation doping (NTD) has demonstrated its initial feasibility in offering precisely controlled and highly uniform dopants within bulk gallium nitride (GaN) wafers. This study aims to assess the doping efficacy of NTD applied to heteroepitaxial GaN films and address the technical challenges related to neutron damage and impurity activation through a comprehensive investigation of neutron irradiation parameters and annealing temperatures. Heteroepitaxial GaN films on sapphire were exposed to neutrons with varying thermal to fast neutron flux ratios in a fission reactor. The results highlight the successful application of the NTD process to heteroepitaxial GaN films, utilizing a relatively harder neutron spectrum with nearly equal thermal and fast neutron fluxes. Notably, a significant activation yield of 95.4 % was achieved through annealing at 1100 °C. Furthermore, the lattice damage and electrical conduction properties of heteroepitaxial GaN films show a strong correlation with the fast neutron fluence and annealing temperature. Elevated annealing temperature promotes the recovery from neutron-irradiated damage and enhances the activation of transmuted dopants. However, some residual defects still persist in neutron-irradiated GaN crystal after annealing. The outcomes of this study are expected to be useful for the establishment of optimal process parameters for NTD-GaN. [ABSTRACT FROM AUTHOR]

To suppress the electric-field crowding at the edge of GaN-based power devices and enhance the breakdown voltage as well, argon ion (Ar+) implantation has been demonstrated an efficient process of edge termination for n-type GaN, that is realized by the introduction of radiation-induced defects to modify electric-field distribution around the edge of devices. However, a high fluence of Ar+ irradiation inevitably causes radiation damage, which is absolutely detrimental to the electrical and material properties of GaN crystal. Therefore, the purpose of this study is to investigate the effects of radiation damage arising from Ar+ implantation on n-type GaN epitaxial layer. 180 keV Ar ions with various fluences ranging from 4.8 × 1013 to 6 × 1015 cm−2 were implanted, forming a thin damaged area near the surface of GaN epitaxial layer. The characteristics of Ar+-implanted GaN epitaxial layer were then thoroughly investigated by Hall effect measurement, X-ray diffraction (XRD), photoluminescence (PL), and Raman scattering spectroscopy. The results indicated that the electron concentration of GaN decreases with the increase of Ar+ fluence. About 32.5 % of carriers in GaN are removed after Ar+ irradiation to a maximum fluence of 6 × 1015 cm−2. As revealed by PL spectra, Ar+ implantation-induced defects would trap free carriers and behave like non-radiative recombination centers. An abrupt increase in lattice strain derived from XRD spectra implies a localized amorphous layer that may be formed in GaN crystal when Ar+ fluence is higher than 1.2 × 1015 cm−2. The Raman spectra also evidenced that Ar+ implantation into GaN leads to N sublattice damage and degradation in electrical conduction properties. The results obtained in this study are expected to be useful for the design of Ar+-implanted edge termination for GaN power devices. [ABSTRACT FROM AUTHOR]

• The burnup credit calculations for PBR spent fuel pebbles were performed using MCNP6. • The impact on the k eff as a function of water density in the storage cask was investigated. • Three single effects and four compound effects were studied. • The mechanisms of all the single and compound effects were researched in depth. This study attempts to investigate the influence due to the use of burnup credit in the criticality safety analysis for pebble-bed reactor (PBR) spent fuel pebbles. Recently, the development of PBR is very quick in China, thus the storage of spent fuel pebbles will become a significant issue in the foreseeable future. For the safe storage, the criticality safety analysis is of vital important. Furthermore, the utilization of burnup credit in the criticality safety analysis is essential due to the fact that it can result in a more compact design of storage system. In this study, all the calculations were performed using MCNP6 associated with the continuous energy neutron data library ENDF/B-VII. In addition, two geometrical models which represent the HTR-10 core and a proposed storage cask were adopted. The proposed storage cask model was established based on the real storage cask for HTR-10 spent fuel pebbles, but the capacity was increased in order to evaluate the impact of burnup credit. Moreover, the most conservative condition for this proposed cask occurs when the cask is full of water with a water density around 0.35 g/cm3. For burnup credit calculations, three operating parameters related to HTR-10 were investigated, including the usage of control rod, the fuel temperature, and the volume fraction of fuel pebbles in total pebbles. Additionally, these operating parameters were combined and classified as three single effects and four compound effects. The single and compound effects were defined as the influence on the effective multiplication factor (k eff) due to simultaneous variations of one and multiple operating parameters, respectively. It is worth noting that in most of the compound effects, the reactivity deviation (or the change of k eff , Δ k) resulting from the compound effect was not a summation of Δ k 's resulting from the associated single effects. This phenomena may affect the precise assessment to some extent. Finally, the mechanisms of both the single and compound effects were explored in depth from the analysis of the spectral distribution of fission. From this analysis, a harder spectral distribution of fission resulting from the single and compound effects corresponds a larger value of Δ k. [ABSTRACT FROM AUTHOR]

• Quasi-vertical Schottky barrier diodes were fabricated on GaN on Si substrate. • The diodes exhibited ultra-low turn on voltage of 0.23 V and ideality factor of 1.02 being close to the ideal value. • Schottky barrier height was extracted from both current–voltage and capacitance–voltage curves. • Experimental current–voltage characteristics are consistent with the simulation results obtained using Silvaco TCAD software. • Temperature dependent reverse leakage current is attributed to variable range hopping mechanisms through dislocations. Quasi-vertical Schottky Barrier Diodes (SBDs) with near to ideal turn-on voltage and ideality factor (n) of 1.02, were fabricated on a GaN on Si substrate. The average turn-on voltage and on-resistance values were found to be 0.23 ± 0.005 V (at 1 A/cm2) and 1.76 ± 0.11 mΩcm2, respectively with diode series resistance of 11 Ω. The analysis of the current–voltage curve revealed a temperature-independent barrier height, however the capacitance–voltage method showed a negative temperature coefficient. This discrepancy is discussed in the paper. Variable range hopping through dislocations is shown to be the dominant reverse current leakage mechanisms identified in the fabricated diode, with a characteristic temperature, T 0 of 2 × 1010 K. [ABSTRACT FROM AUTHOR]

Highlights • The burnup credit calculations for PWR spent fuel assemblies were performed. • Six single effects and eight compound effects were studied. • The Δ k caused by both single and compound effects were investigated. • The mechanisms of both single and compound effects were studied. Abstract This study attempted to thoroughly investigate the impact of single and compound effects on burnup credit calculations for PWR spent fuel assemblies originating from various operating parameters. Three operating parameters were considered, including fuel temperature, boron concentration, and axial burnup profile. The single and compound effects defined in this study represent the influence caused by simultaneous variations of one and multiple operating parameters on the curve of effective multiplication factor (k eff) versus burnup (B), respectively. All the calculations were performed using SCALE 6.1 computer code together with the ENDF/B-VII 238-group data library. In addition, two geometrical models were established based on the Westinghouse 17 × 17 PWR optimized fuel assembly and GBC-32 storage cask. The results revealed that an increase of fuel temperature or boron concentration induces a positive reactivity deviation (or the change of k eff , Δ k), the opposite is also true when a decrease of fuel temperature or boron concentration is considered. Moreover, the utilization of non-uniform axial burnup profile leads to a positive Δ k. Additionally, in most of the compound effects, Δ k resulting from the compound effects was not a linear summation of the Δ k 's resulting from the associated single effects. In particular, such Δ k discrepancy increases as B increases, which could influence the precise assessment of burnup credit to some extent. The mechanisms of both the single and compound effects were studied by the analysis of the spectral distribution of fission. From this analysis, an increase of either fuel temperature or boron concentration leads to a harder neutron spectrum, while a non-uniform axial burnup profile leads to a softer one. [ABSTRACT FROM AUTHOR]

Abstract As compared to the conventional smart-cut technology based on single H ion implantation, sequential implantation of H and He ions has been demonstrated to be effective in reducing the implantation fluence and the thermal budget needed for Si layer splitting process. However, the sequential implantation method involves complicated process parameters such as ion energy and implantation sequence. The purpose of this study is to clarify the dependence of He ion energy on Si blistering characteristics by sequential implantation of H and He ions into Si in various sequences. The accelerated energy of H ions was fixed at 40 keV, while that of He ions was changed to 30, 50, and 70 keV. Both the implantation fluences of H and He ions were 1 × 1016 cm−2. The non-isothermal and isothermal annealing methods in combination with an in-situ optical microscopy (OM) detection system were adopted to determine the threshold temperatures and the onset times for blister and crater formation as well as to examine the thermal evolution of blisters and craters. The results revealed that the threshold temperatures for blister and crater formation are highly correlative to the He ion energy and implantation sequence. Higher He ion energy is preferable to blistering for the specimens first implanted with He ions, but the opposite is true for the reverse implantation sequence. This statement can be also supported by the activation energy levels required for blister and crater formation obtained from kinetics analysis. In addition, the variation of hydrogenated complexes induced by sequential implantation and annealing can be evidently identified from the Raman spectra, showing a noticeable transformation of H-related defect complexes from VH 3 to Si(100):H bonding configuration due to the emergence of blisters and craters. Highlights • H/He sequential implantation is proved to be effective for smart-cut technology. • Two-step ion implantation process varied in sequence and He ion energy was done. • Blistering characteristics were assessed using quantitative and kinetics analysis. • Blistering effectiveness depends on implantation sequence and He ion energy. [ABSTRACT FROM AUTHOR]

In this study, the displacement damage dose (DDD) effects of proton irradiation on bulk crystal and interfacial properties of 4H-SiC MOS capacitors (MOSCs) were investigated. The Monte Carlo calculation code named SRIM (Stopping and Range of Ions in Matter) was first used to predict the depth profiles and damage distributions of protons. The 4H-SiC MOSCs were irradiated with 60, 100, 150 keV protons to fluences ranging from 5 × 1011 to 5 × 1013 cm−2. Capacitance-voltage (C-V) curves of the MOSCs were then measured to characterize the variation of the electrically active defects in 4H-SiC MOSCs. The results revealed that the non-ionization energy loss of incident protons leads to the accumulation of the primary defects in bulk SiC crystal as well as the increase of the interface traps between SiO 2 and SiC crystal. A distinctive bump phenomenon was found in the weak inversion region of the C-V curve and it became more prominent with the increase of proton fluence, providing evidence for the existence of bulk traps. Furthermore, the incident proton energy is also a crucial factor in interface deterioration, suggesting that more interface traps would be formed when the proton damage peak is closer to the SiO 2 /SiC interface. • Displacement damage effects of proton irradiation on 4H-SiC MOSCs were investigated. • Non-ionization energy loss of protons leads to the buildup of bulk and interface traps. • A distinctive bump in weak inversion region of C V curve implies the existence of bulk traps. • Lowering proton incident energy accelerates the interface deterioration of SiC MOSCs. [ABSTRACT FROM AUTHOR]

This study employs nuclide sensitivity coefficients to investigate the spent fuel reactivity of pressurized water reactors (PWRs) in terms of differences in predicted inventories under various depletion conditions. Considering a representative PWR spent fuel, the study began by selecting the top 20 nuclides of large macroscopic neutron absorption cross sections, which are expected to have a substantial effect on reactivity. The sensitivity coefficients (Δ k ∞ /Δ N i ) of each nuclide were first evaluated at various burnups and cooling times using MCNPX. These coefficients were used to facilitate a detailed analysis of the spent fuel reactivity and to identify which nuclides cause the effect in a quantitative manner. The approach was demonstrated by analyzing the effects on spent fuel reactivity of several depletion parameters, including the initial enrichment, specific power, operating history, boron concentration, fuel temperature, moderator temperature, control rod effect, and axial burnup profile. The results were generally in good agreement with those obtained from direct MCNPX criticality calculations. Two major advantages of this approach are: (1) the changes in spent fuel reactivity with various depletion parameters can be closely related to composition changes; and (2) it provides a quantitative estimate of the contribution of each nuclide to the reactivity effect based on the predicted inventory differences. [ABSTRACT FROM AUTHOR]

• The varying amounts of proton beams result in different minor actinide burnup. • Single proton beam leads to an uneven neutron flux on the fuel assembly. • The dual proton beam possesses the highest neutron importance and burnup. This study aims to identify the optimal beam design for incinerating the long-lived minor actinides in Accelerator-Driven System (ADS). All the analyses were performed using the MCNP6.1 code with cross-section library ENDF/B-VII. In this study, a depletion method for ADS was conducted and analyses were exercised to investigate the burnup performances for the various arrangements of a three-proton beam design. The influences of the various arrangements of the three-proton beam design were used as a criterion for comparison. It was found that the dual proton beam arrangement demonstrated the best depletion result for the incineration of minor actinides. [ABSTRACT FROM AUTHOR]

The ion-cut technology used for the fabrication of Silicon-On-Insulator (SOI) substrates involves a thermally activated layer splitting process with the evolution of hydrogenated defect complexes into microcracks in H-implanted Si. Since the layer splitting process is highly correlated to the interaction of H atoms with defects, it is expected that the blistering kinetics arising from H implantation would vary with crystal plane orientation of Si substrates. This study presents a thorough investigation of the influence of crystal plane orientation on the blistering kinetics and defect evolution in H-implanted Si. Three Si substrates of Si(100), Si(111), and Si(110) were implanted with H 2 + ions at an accelerated energy of 40 keV to a fluence of 2.5 × 1016 cm−2. After ion implantation, the blistering characteristics, defect complexes, and microstructure of the specimens were characterized by SIMS, in-situ OM observation system, Raman spectra, and XTEM. The results revealed that two limiting steps of H atom diffusion dominate the blistering process in different temperature intervals. The transformation of VH 3 (or V 2 H 6) defect complex into Si:H surface state is mainly prevailing in the low-temperature interval. The blistering characteristics of Si showed a high correlation with the crystal plane orientation of Si substrates due to the difference in planar atomic density. Si(110) having a largest planar atomic density corresponds to a highest threshold temperature and a longest onset time for blister formation, followed by Si(111) and Si(100) in turn. The correlation between blistering characteristics and substrate orientation can be attributed to the fact that H implantation leads to different densities of the H-terminated platelets in Si specimens with various planar atomic densities, thus affecting the efficiency of free H atom diffusion into platelets and the blister growth as well. A conclusive finding from this study is that substrate orientation diversifies the defect density in damage layer caused by hydrogen implantation, which could change the nucleation sites of platelets available for blister formation and eventually influence the blistering efficiency and microcrack extension. • Blistering kinetics of H-implanted Si varies with crystal plane orientation. • Two limiting factors dominate blistering in low- and high-temperature intervals. • A higher density of platelets due to a greater planar atomic density retards blistering. • Si(110) has a reduced blistering efficiency but a better microcrack extension. [ABSTRACT FROM AUTHOR]

This study aims to propose a model for dynamically simulating the online-refueling process in pebble-bed reactor (PBR) using MCNPX. PBR has a special feature of online-refueling which can greatly reduce the outage time and enable a higher burnup in spent fuel. However, this feature also results in the dynamical fuel movements which may significantly increase the difficulty and the computational time in computer simulation. Therefore, an appropriate model is necessary to be proposed to simulate the burnup characteristics of online-refueling and to reduce the computational time simultaneously. All the calculations in this study were performed using MCNPX 2.7.0 with the ENDF/B-VII continuous energy nuclear data library. The PBR model was built according to the core design of HTR-10 but adopted some reasonable assumptions. The refueling process was emulated by utilizing the fuel loading scenario of the once through then out (OTTO) in combination with the layer-mixed-shell fuel movement. Additionally, the layer-mixed-shell fuel movement considered the concept of fuel channels, where the fuel pebbles only move in the same fuel channel, such that the burnup characteristics of fuel pebbles in both radial and axial direction can be identified separately. The core was divided into 9 fuel zones with a fixed volume and 3 fuel channels with a variety of fuel zones. Furthermore, the number of fuel zones in each fuel channel was determined based on the relative residence time of fuel pebbles in the core. The results revealed that the core can achieve an equilibrium fuel cycle after refueling several times, and after that all the core characteristics can nearly maintain unchanged between different cycles. Although the refueling process was modeled based on the OTTO fuel loading scenario instead of the multi-pass one, the discharged burnup can still reach the target burnup of the spent fuel for HTR-10, i.e. 72 GWd/tHM. In addition, the average discharged burnup under the equilibrium fuel cycle is approximate to 80 GWd/tHM, which also coincides the design value of the spent fuel for HTR-10. Therefore, the layer-mixed-shell movement model can consider the fuel movements in either radial or axial directions simultaneously and enable a more accurate prediction to the real refueling process of HTR-10 than our previous studies. • A proposed model for the dynamical simulation of PBR. • Both the axial and burnup characteristics were performed. • The core can achieve an equilibrium fuel cycle. • The average discharged burnup can reach the design value of HTR-10. [ABSTRACT FROM AUTHOR]

Multilayer antimonene nanoribbons with room temperature orange light emission uniformly distributed on InSb were synthesized by the plasma-assisted process. The bandgap opening was caused by the quantum confinement effect of the nanoribbon structure and the turbostratic stacking of antimonene layers. This attractive two-dimensional material, whose band structure is proper for applications of transistors and light-emitting diodes, was first synthesized. [ABSTRACT FROM AUTHOR]

In recent years, gold (Au) nanoparticles have been synthesized via various methods and used in optical and biomedical detection. Au nanoparticles contain some remarkable dimension-dependent optical properties due to surface plasmon resonance (SPR) in Au nanoparticles which causes high absorption in visible light regions. Since SPR in well-crystallized Au nanoparticles can enhance the local electromagnetic field, it is thus expected that greater efficiency in the photoluminescence (PL) originating from oxygen deficiency centers (ODC) can be achieved in Au-implanted SiO 2 matrix. In order to demonstrate the enhancement of PL, Au nanoparticles were formed in SiO 2 film using ion beam synthesis and their optical and microstructural properties were also investigated in this study. The results revealed that a clear absorption peak at approximately 530 nm was identified in the UV-Vis spectra and was attributed to SPR induced by Au nanoparticles in SiO 2 . The SPR of Au nanoparticles is also dependent on thermal treatment conditions, such as post-annealing temperature and ambient. The Au nanoparticle-containing SiO 2 film also displayed several distinctive peaks at approximately 320, 360, 460, and 600 nm in the PL spectra and were found to be associated with ODC-related defects and non-bridging oxygen hole centers (NBOHC) in SiO 2 . In addition, the PL peak intensities increased as post-annealing temperature increased, a finding contradictory to the defect recovery but highly consistent with the SPR tendency. A maximum PL emission was achieved when the Au-implanted SiO 2 film was annealed at 1100 °C for 1 h under N 2 . Therefore, the existence of Au nanoparticles in SiO 2 film can induce SPR effects as well as enhance PL emission resulting from defect-related luminescence centers. [ABSTRACT FROM AUTHOR]

The mechanisms of photoluminescence (PL) originating from Si + /C + implanted SiO 2 are still unclear and need to be clarified. Thus, the purpose of this study is to thoroughly investigate the effects of ion implantation and post-annealing temperature on microstructures and PL characteristics of the Si + /C + implanted SiO 2 films. A comparative analysis was also conducted to clarify the different optical properties between the Si + and Si + /C + implanted SiO 2 films. In this study, thermally-grown SiO 2 films on Si substrates were used as the matrix materials. The Si + ions and C + ions were separately implanted into the SiO 2 films at room temperature. After ion implantation, the post-annealing treatments were carried out using the furnace annealing (FA) method at various temperatures (600–1100 °C) for 1 h in a N 2 ambient. The PL characteristics of the implanted SiO 2 films were analyzed using a fluorescence spectrophotometer. The results revealed that the distinct PL peaks were observed at approximately 310, 450 and 650 nm in the Si + -implanted SiO 2 films, which can be attributed to the defects, the so-called oxygen deficiency centers (ODCs) and non-bridging oxygen hole centers (NBOHCs), in the materials. In contrast to the Si + ion implantation, the SiO 2 films which were sequentially implanted with Si + and C + ions and annealed at 1100 °C can emit white light corresponding to the PL peaks located at around 420, 520 and 720 nm, those can be assigned to the Si–C bonding, C–C graphite-like structure (sp 2 ), and Si nanocrystals, respectively. Moreover, a correlation between the optical properties, microstructures, and bonding configurations of the Si + /C + implanted SiO 2 films was also established in this study. [ABSTRACT FROM AUTHOR]

Abstract: This study performs an investigation of geometry homogenization simulation using MCNP5 v1.51 and SCALE6 on the HTR-10 criticality calculations and focusing on the impact of geometry homogenization on k eff and neutron spectrum. The data libraries employed in this work are both continuous ENDF/B-VI respectively in MCNP5 and SCALE6. Six models, which are Model 1 – heterogeneous model, Model 2 – TRISO coating and graphite matrix homogenized model, Model 3 – TRISO homogenized model, Model 4 – fuel zone of fuel ball homogenized model, Model 5 – fuel ball homogenized model, and Model 6 – core homogenized model, are performed correspondingly by using MCNP5 and SCALE6 on the homogeneous effect analysis in HTR-10. The results revealed that the differences of k eff between MCNP5 and SCALE6 are all less than 300pcm. The small differences of k eff, neutron spectra, and also the consistent discrepancies of neutron spectra between each homogenized model (Model 2–6) and Model 1 show the good agreement of MCNP5 with SCALE6 in the geometry homogenization. [Copyright &y& Elsevier]

Highlights: [•] Comparisons of the HTR-10 criticality calculations with SCALE6/CSAS6 and MCNP5 were performed. [•] The DOUBLEHET unit-cell treatment provides the best k eff estimation among PBR criticality calculations using SCALE6. [•] The continuous-energy SCALE6 calculations present a non-negligible discrepancy with MCNP5 in three PBR cases. [ABSTRACT FROM AUTHOR]

Abstract: Crystallization and thermal stability of Ge2Sb2Te5 (GST), the benchmark working material in phase-change non-volatile memory, were modified via Si-ion implantation. Through 5×1015 Si-ions/cm2 ion-implantation, crystallization temperature increases from 165°C to 177°C. Furthermore, the activation energy of crystallization increases from 2.9eV in the pristine film to 3.3eV and 4.0eV in films implanted with the doses of 5×1015 and 5×1016 Si-ions/cm2, respectively. Temperatures corresponding to a 10-year failure-time increase from 83°C in the pristine film to 96°C and 107°C in films implanted with 5×1015 and 5×1016 Si-ions/cm2, respectively. Thermal stability of Si-ion implanted GST thus improves significantly. It was also found that grain growth is inhibited with higher implantation doses. In the case of the 5×1016 ion/cm2 dose, the second-phase transition from face-centered cubic to hexagonal closed-packed structure of the GST is completely inhibited. However, crystallization time increases slightly due to Si-ion implantation. [Copyright &y& Elsevier]

This study aims to investigate the neutronic characteristics of spallation targets for Accelerator-Driven subcritical System (ADS) and find the optimal target design for reducing the strength of the required beam current. All the calculations were conducted using the MCNP6.1 with cross-section library ENDF/B-VII. In this study, the influence of several parameters on spallation targets is investigated, such as neutron production with various spallation target layouts, spallation neutron distribution with different proton beam energy levels, and spallation neutron spectrum. • Neutron production analysis with different spallation target geometries. • Spatial and energy neutron flux distribution for spallation target. • Fixed-source problem simulation with high proton beam fixed-source. [ABSTRACT FROM AUTHOR]

• A modified simulation model in MCNP 6.1 was developed for the dynamic HTR-10 core. • Applying the composition library can simplify processes with accurate results. • Due to longer residual time, the discharge burnup in the outer channel is higher. • Core power distribution using multi-pass refueling is more uniform compared to OTTO. This study aims to precisely investigate the core characteristics of HTR-10 using an online-refueling fuel loading scenario through an innovative approach that incorporates a pre-generated fuel composition library. HTR-10 is an experimental high-temperaturegas- cooled pebble-bed reactor constructed in China. Applying multi-pass fuel loading scenario, the pebbles in HTR-10 pass through the core several times via onlinerefueling. In this study, we proposed a model that simulates the dynamic operation of HTR-10 by using continuously static calculations. The model was constructed by dividing the core into 3 flow channels with different amounts of horizontal zones according to the residence time of fuel pebbles. However, random distribution of the pebbles with various burnup values complicates the refueling process. In order to simulate online-refueling more conveniently, a comprehensive method based on multipass fuel loading scenarios was thus developed. Firstly, a pre-generated fuel composition library containing the content of both actinides and fission products of fuel pebbles as a function of burnup, was built by implementing full core depletion calculations. During the refueling processes, a specific ratio of discharged fuel pebbles to fresh fuel pebbles was reloaded into the top zones. Thus, the average burnup values in the top zones can be resulted by considering the supplement of fresh fuel pebbles. Eventually, the fuel composition in the top zones were obtained by interpolating the average burnup value from the pre-generated library. In this study, all the calculations were performed using the MCNP6 computer code together with the ENDF/B-VII continuous energy neutron data library. The results revealed that the core reached a state of equilibrium after seven refueling processes with an increased rate of volume fraction. Our findings correspond to those of other studies. Another model constructed by locating the actual distribution of fresh pebbles also confirms the verification of the refueling method. Eventually, the burnup characteristics as well as the power and flux distributions in the HTR-10 core were analyzed using the simulation method. [ABSTRACT FROM AUTHOR]

• The irradiation-induced swelling effect were significantly suppressed in HfNbTaTiZr refractory high-entropy alloy. • The nanoindentation hardness after the irradiation was almost unchanged. • The radiation damage range far exceeded the simulated results and the range of implanted species. The lattice distortion and diffusion kinetics of refractory high-entropy alloys (RHEAs), which may be endowed with superior radiation tolerance, render RHEAs candidate materials for nuclear and aerospace systems. To investigate the irradiation behavior of body-centered cubic (BCC) RHEAs, the specimens were irradiated by 300 keV Ni+ to a fluence of 1.5 × 1016 cm−2 at 100 °C, reaching a high damage level to over 30 displacements per atom (dpa). The results revealed that the swelling and hardening effects were significantly suppressed compared to those of conventional nuclear materials. Further microstructural characterization showed that the damage range far exceeded the simulated results and the range of implanted species. [ABSTRACT FROM AUTHOR]

The UK nuclear innovation programme supported by the government includes preparation for future ABWR construction. The UK has significant expertise in building and operating gas-cooled nuclear reactors and some experience with PWRs, while there is limited knowledge in BWR technologies. Hence, an important aim of this work is to understand the discrepancies between codes to assess uncertainties in BWR lattice and depletion calculations, while identifying specific development demands to progress existing tools into extended applications. The objective of the study is to quantify the discrepancy between SCALE-6.2, CASMO5 and the UK WIMS-10A deterministic lattice code for BWR lattice and burnup modelling. Two models of BWR systems were considered for this new systematic comparison. They are a single BWR pin-cell with UO2 fuel only, and a 3 by 3 array of BWR UO2 fuel rods with gadolinia rod in the centre. Criticality over burnup was estimated for both models using these codes. Spectral indexes, number densities and neutron spectrum were compared for several burnup stages using SCALE-6.2 and WIMS-10A. The study showed that kinf obtained with CASMO5 was in a good agreement with the SCALE-6.2. A clear discrepancy in behaviour was observed between WIMS-10A and SCALE-6.2 as well as CASMO5. [ABSTRACT FROM AUTHOR]