The results of an accident analysis for the loss of offsite power(LOOP)scenario in a reference Bushehr-1 VVER-1000/V446 nuclear power plant(NPP)are presented in this paper.This study attempted to provide a better anal...The results of an accident analysis for the loss of offsite power(LOOP)scenario in a reference Bushehr-1 VVER-1000/V446 nuclear power plant(NPP)are presented in this paper.This study attempted to provide a better analysis of LOOP accident management by integrating deterministic and probabilistic approaches.The RELAP5 code was used to investigate the occurrence of specific thermal–hydraulic phenomena.The probabilistic safety assessment of the LOOP accident is presented using the SAPHIRE software.LOOP accident data were extracted from the Bushehr NPP final safety analysis reports and probabilistic safety analysis reports.A deterministic approach was used to reduce the core damage frequency in the probabilistic analysis of LOOP accidents.The probabilistic approach was used to better observe the philosophy of defense in depth and safety margins in the deterministic analysis of the LOOP accident.The results show that the integration of the two approaches in LOOP accident investigations improved accident control.展开更多
A burnup calculation was performed to analyze the Apr`es ORIENT process, which aims to create highlyvaluable elements from fission products separated from spent nuclear fuels. The basic idea is to use nuclear transmut...A burnup calculation was performed to analyze the Apr`es ORIENT process, which aims to create highlyvaluable elements from fission products separated from spent nuclear fuels. The basic idea is to use nuclear transmutation induced by a neutron capture reaction followed by a β-decay, thus changing the atomic number Z of a target element in fission products by 1 unit. LWR(PWR) and FBR(MONJU) were considered as the transmutation devices. High rates of creation were obtained in some cases of platinum group metals(44Ru by FBR,46 Pd by LWR) and rare earth(64Gd by LWR,66 Dy by FBR). Therefore, systems based on LWR and FBR have their own advantages depending on target elements. Furthermore, it was found that creation rates of even Z(= Z + 1) elements from odd Z ones were higher than the opposite cases. This creation rate of an element was interpreted in terms of "average 1-group neutron capture cross section of the corresponding target element σc Z defined in this work. General trends of the creation rate of an even(odd) Z element from the corresponding odd(even) Z one were found to be proportional to the 0.78th(0.63th) power of σc Z, however with noticeable dispersion. The difference in the powers in the above analysis was explained by the difference in the number of stable isotopes caused by the even-odd effect of Z.展开更多
The treatment and disposal of radioactive waste are presently facing great challenges.Spent ion exchange resins have become a focus of attention due to their high production and serious environmental risks.In this pap...The treatment and disposal of radioactive waste are presently facing great challenges.Spent ion exchange resins have become a focus of attention due to their high production and serious environmental risks.In this paper,a simplified model of cationic exchange resin is proposed,and the degradation processes of cationic resin monomer initiated by hydroxyl radicals(·OH)are clarified by combining statistical molecular fragmentation(SMF)model and density functional theory(DFT)calculations.The prediction of active sites indicates that the S-O bonds and the C-S bond of the sulfonic group are more likely to react during the degradation.The meta-position of the sulfonic group on the benzene ring is the most active site,and the benzene ring without the sulfonic group has a certain reactivity.The C11-C14 and C17-C20 bonds,on the carbon skeleton,are the most easily broken.It is also found that dihydroxy addition and elimination reactions play a major role in the process of desulfonation,carbon skeleton cleavage and benzene ring separation.The decomposition mechanisms found through the combination of physical models and chemical calculations,provide theoretical guidance for the treatment of complex polycyclic aromatic hydrocarbons.展开更多
W-based WTaVCr refractory high entropy alloys (RHEA) may be novel and promising candidate materials for plasma facing components in the first wall and diverter in fusion reactors. This alloy has been developed by a po...W-based WTaVCr refractory high entropy alloys (RHEA) may be novel and promising candidate materials for plasma facing components in the first wall and diverter in fusion reactors. This alloy has been developed by a powder metallurgy process combining mechanical alloying and spark plasma sintering (SPS). The SPSed samples contained two phases, in which the matrix is RHEA with a body-centered cubic structure, while the oxide phase was most likely Ta2VO6through a combined analysis of X-ray diffraction (XRD),energy-dispersive spectroscopy (EDS), and selected area electron diffraction (SAED). The higher oxygen affinity of Ta and V may explain the preferential formation of their oxide phases based on thermodynamic calculations. Electron backscatter diffraction (EBSD) revealed an average grain size of 6.2μm. WTaVCr RHEA showed a peak compressive strength of 2997 MPa at room temperature and much higher micro-and nano-hardness than W and other W-based RHEAs in the literature. Their high Rockwell hardness can be retained to at least 1000°C.展开更多
The shielding and corrosion properties of the Alloy 709 advanced austenitic stainless steel have been investigated as a candidate canister material in spent fuel dry casks.The results revealed that the experimental an...The shielding and corrosion properties of the Alloy 709 advanced austenitic stainless steel have been investigated as a candidate canister material in spent fuel dry casks.The results revealed that the experimental and computational data of the linear and mass attenuation coefficients of the alloy are in good agreement,in which the attenuation coefficient values decreased with increasing photon energy.Alloy 709 was shown to exhibit the highest linear attenuation coefficient against gamma rays when compared to 304 and 316 stainless steels.On the other hand,Alloy 709 exhibited no considerable weight change over a 69-day period in circulating salt brines corrosion testing,while it showed an exponential increase of corrosion current density with temperature in acidic and basic corrosive solutions during electrochemical polarization corrosion testing.Furthermore,Alloy 709 was the least corroded steel compared to other austenitic stainless steels in both acidic and basic solutions.The optimistic results of the shielding and corrosion properties of Alloy 709 due to its chemical composition,suggest utilizing it as a canister material in spent nuclear fuel dry casks.展开更多
Small modular reactors (SMRs) offer simple, standardized, and safe modular designs for new nuclear reactor construction. They are factory built, requiring smaller initial capital investment and facilitating shorter co...Small modular reactors (SMRs) offer simple, standardized, and safe modular designs for new nuclear reactor construction. They are factory built, requiring smaller initial capital investment and facilitating shorter construction times. SMRs also promise competitive economy when compared with the current reactor fleet. Construction cost of a majority of the projects, which are mostly in their design stages, is not publicly available, but variable costs can be determined from fuel enrichment, average burn-up, and plant thermal efficiency, which are public parameters for many near-term SMR projects. The fuel cost of electricity generation for selected SMRs and large reactors is simulated, including calculation of optimal tails assay in the uranium enrichment process. The results are compared between one another and with current generation large reactor designs providing a rough comparison of the long-term economics of a new nuclear reactor project. SMRs are predicted to have higher fuel costs than large reactors. Particularly, integral pressurized water reactors (iPWRs) are shown to have from 15% to 70% higher fuel costs than large light water reactors using 2014 nuclear fuels market data. Fuel cost sensitivities to reactor design parameters are presented.展开更多
This paper investigates long-term energy strategy compatible with significant reduction of world carbon dioxide （CO2） emissions, employing a long-term global energy model, Dynamic New Earth 21 （called DNE21）. The ...This paper investigates long-term energy strategy compatible with significant reduction of world carbon dioxide （CO2） emissions, employing a long-term global energy model, Dynamic New Earth 21 （called DNE21）. The model seeks the optimal energy mix from 2000 to 2100 that minimizes the world total energy system cost under various kinds of energy and technological constraints, such as energy resource constraints, energy supply and demand balance constraints, and CO2 emissions constraints. This paper discusses the results of primary energy supply, power generation mix, CO2 emission, CCS （carbon capture and storage） and total system costs for six regions including world as a whole. To evaluate viable pathways forward for implementation of sustainable energy strategies, nuclear power generation is a viable source of clean and green energy to mitigate the CO2 emissions. Present research shows simulation results in two cases consisting of no CO2 regulation case （base case） and CO2 REG case （regulation case） which halves the world CO2 emissions by the year 2050. Main findings of this research describe that renewable and nuclear power generation will contribute significantly to mitigate the CO2 emission worldwide.展开更多
Dose estimation and quality control in computed tomography (CT) scanners are useful in controlling the dose of radiation given to patients while tests are carried out. The study was performed in a 16-slice Computed To...Dose estimation and quality control in computed tomography (CT) scanners are useful in controlling the dose of radiation given to patients while tests are carried out. The study was performed in a 16-slice Computed Tomography (CT) system of LightSpeed RT16 Xtra CT scanner. Quality control was done using a vendor-provided QA Phantom, and the six aspects of image quality were measured. For CT dosimetry, Computed Tomography Dose index volume (CTDIvol) was performed using Computed Tomography Dose Index (CTDI) Phantom. CTDI Phantom consists of three parts: Pediatric Head, Adult Head, and Adult Body Phantom. A 10 cm long pencil ion chamber DCT-10 was used to measure the dose at different positions inside the CTDI Phantom. Data were collected using MagicMax Universal software. For dose estimation of the CTDIvol Report of AAPM Task Group, 96 and 111 formalisms were used. For Pediatric Head, Adult Head, and Adult Body Phantom the measured CIDIvol was 61.04 mGy, 48.11 mGy, and 18.08 mGy respectively. The study has shown deviations of 7%, 15%, and 19% between estimated and console-displayed doses for Pediatric Head, Adult Head, and Adult Body scan techniques respectively. The six aspects of image quality measured by QA Phantom were found to be compatible with the specifications of the machine and CTDIvol measured by CTDI Phantom were found within a tolerance limit of ±20%. Hence, the QC and dosimetry of the mentioned machine are within the limit.展开更多
Transition metal(oxy)hydroxides are potential oxygen evolution reaction(OER)electrocatalysts;however,simultaneously modulating multiple factors to enhance their performance is a grand challenge.Here,we report an incor...Transition metal(oxy)hydroxides are potential oxygen evolution reaction(OER)electrocatalysts;however,simultaneously modulating multiple factors to enhance their performance is a grand challenge.Here,we report an incorporating heteroatom strategy via one-step hydrothermal approach to adjust more than one factor of Mn-doped NiFe(oxy)hydroxide(Mn-NiFeOOH/LDH)heterojunction.Mn doping regulates heterojunction morphology(reducing nanoparticles and becoming thinner and denser nanosheets),Ni/Fe ratio and valence states(Ni^(2+),Ni^(3+),and Ni^(3+Δ))of Ni ions.The former could effectively increase surface active sites,and the latter two reduce the content of Fe in the Mnx-NiFeOOH/LDH heterojunction,en-abling more Ni^(2+)convert to Ni^(3+/3+Δ)that have higher intrinsic OER activity.As a result,the first-rank Mn-NiFeOOH/LDH with ultra-low overpotential of 185 mV@20 mA cm^(-2) and 296 mV@500 mA cm^(-2),and the improved OER performance are outdo to those of commercial RuO_(2) catalyst for OER.Moreover,the Mn-NiFeOOH/LDH affords the earliest initial potential(1.392 V vs.RHE),corresponds to a recorded low overpotential(162 mV).Based on the density functional theory(DFT),Mn dopants can alter intermedi-ate adsorption energy and effectively decrease∗OOH’s energy barrier.This research exhibits a feasible strategy to design low cost electrocatalysts and provide new possibilities for future industrialization.展开更多
Advancing 3D magnesium(Mg)development beyond current limitations requires controlling Mg alloy degradation in pre-designed,low-dimension architectures.This study reveals a mechanistic switch in the corrosion behavior ...Advancing 3D magnesium(Mg)development beyond current limitations requires controlling Mg alloy degradation in pre-designed,low-dimension architectures.This study reveals a mechanistic switch in the corrosion behavior of Mg alloy(3.6%Al,0.8%Zn)diamond lattice structures,induced by plasma nanosynthesis(400 eV Ar^(+)ions,fluence 1×10^(17) ions/cm^(2)).Plasma treatment of the Mg alloy increases surface Mg from 1.5%to 14.5%,enhances carbonate formation,and generates a nanostructured surface with a Mg carbonate layer over an oxide/hydroxide layer.In vitro and in vivo analyses over 8 wk demonstrate how this treatment fundamentally alters the degradation process and stability of these 3D architectures.While untreated samples initially formed a protective film that subsequently diminished,DPNS-treated samples demonstrated an inverse corrosion behavior.X-ray photoelectron spectroscopy(XPS)and electrochemical impedance spectroscopy(EIS)confirmed the presence of a stable,protective layer composed of magnesium oxide,magnesium hydroxide,and magnesium carbonate on the DPNS-treated surfaces.After 14 days,the DPNS-treated sample exhibited a more positive corrosion potential(-0.69 V versus-1.36 V)and a marginally lower current density(0.73 mA/cm^(2)compared to 0.75 mA/c^(2))relative to the control.This protective layer,combined with modified surface topology,initiated a core-to-periphery degradation pattern that maintained structural integrity for up to 8 wk post-implantation.These findings support the conclusion that the DPNS-treated scaffold demonstrates sustained improved corrosion resistance over time compared to the untreated control.Micro-CT revealed plasma-treated samples retained larger struts(504.9±95.3μm at 8 wk)and formed larger H_(2) pockets extending 14.2 mm from the implant center,versus 4.9 mm in controls.This corrosion behavior switch enhances stability but risks pore clogging,offering insights for tailoring Mg alloy degradation and H_(2) evolution in 3D architectures for biomedical applications.展开更多
Tungsten(W)is the leading plasma-facing candidate material for the International Thermonuclear Experimental Reactor and next-generation fusion reactors.The impact of synergistic helium(He),irradiation-induced microstr...Tungsten(W)is the leading plasma-facing candidate material for the International Thermonuclear Experimental Reactor and next-generation fusion reactors.The impact of synergistic helium(He),irradiation-induced microstructural changes,and the corresponding thermal-mechanical property degradation of W are critically important but are not well understood yet.Predicting the performance of W in fusion environments requires understanding the fundamentals of He-defect interactions and the resultant He bubble nucleation and growth in W.In this study,He retention in helium-ion-implanted W was assessed using neutron depth profiling(NDP),laser ablation mass spectrometry(LAMS),and thermal desorption spectroscopy(TDS)following 10 keV room-temperature He implantation at various fluences.These three experimental techniques enabled the determination of the He depth profile and retention in He-implanted W.A cluster dynamics model based on the diffusion-reaction rate theory was applied to interpret the experimental data.The model successfully predicted the He spatial depth-dependent profile in He-implanted W,which was in good agreement with the LAMS measurements.The model also successfully captured the major features of the He desorption spectra observed in the THDS measurements.The NDP quantified total He concentration values for the samples;they were similar to those estimated by LAMS.However,the depth profiles from NDP and LAMS were not comparable due to several factors.The combination of modeling and experimentation enabled the identification of possible trapping sites for He in W and the evolution of He-defect clusters during the TDS thermal annealing process.展开更多
Recently, high-entropy alloys(HEAs) or multi-principal-element alloys with unprecedented physical,chemical, and mechanical properties, have been considered as candidate materials used in advanced reactors due to their...Recently, high-entropy alloys(HEAs) or multi-principal-element alloys with unprecedented physical,chemical, and mechanical properties, have been considered as candidate materials used in advanced reactors due to their promising irradiation resistant behavior. Here, we report a new single-phase bodycentered cubic(BCC) structured Ti_2 ZrHfV_(0.5)Mo_(0.2) HEA possessing excellent irradiation resistance, i.e.,scarcely irradiation hardening and abnormal lattice constant reduction after helium-ion irradiation,which is completely different from conventional alloys. This is the first time to report the abnormal XRD phenomenon of metallic alloys and almost no hardening after irradiation. These excellent properties make it to be a potential candidate material used as core components in next-generation nuclear reactors. The particular irradiation tolerance derives from high density lattice vacancies/defects.展开更多
The phenomenon of direct-contact condensation,used in steam driven jet injectors,nuclear reactor emergency core cooling systems and direct-contact heat exchangers,was investigated computationally by introducing a ther...The phenomenon of direct-contact condensation,used in steam driven jet injectors,nuclear reactor emergency core cooling systems and direct-contact heat exchangers,was investigated computationally by introducing a thermal equilibrium model for direct-contact condensation of steam in subcooled water.The condensation model presented was a two resistance model which takes care of the heat transfer process on both sides of the interface and uses a variable steam bubble diameter.The injection of supersonic steam jet in subcooled water tank was simulated using the Euler-Euler multiphase flow model of Fluent 6.3 code with the condensation model incorporated. The findings of the computational fluid dynamics（CFD） simulations were compared with the published experimental data and fairly good agreement was observed between the two,thus validating the condensation model.The results of CFD simulations for dimensionless penetration length of steam plume varies from 2.73-7.33,while the condensation heat transfer coefficient varies from 0.75-0.917 MW·（m ^2 ·K）^ -1 for water temperature in the range of 293-343 K.展开更多
This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at t...This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at three positions: contact detonation in the center, contact detonation above the web and close-in detonation in the center. The external and internal breach parameters of the panels were evaluated by measuring the diameter of the ejection crater, spalling crater and breach hole created by the charge detonation. The experimental results were compared to predict values obtained by the analytical models proposed by McVay, Morishita and Remennikov. A modified breach with crater limit line and breach without crater limit line were put forward based on the experimental results. The maximum cross-sectional destruction area ratio(MCDAR) values were used to evaluate the damage degree. The maximum value of MCDAR reached 0.331 corresponding to the C5 experimental condition, of which explosion occurred above the web.展开更多
Muon scattering tomography is believed to be a promising technique for cargo container inspection, owing to the ability of natural muons to penetrate into dense materials and the absence of artificial radiation. In th...Muon scattering tomography is believed to be a promising technique for cargo container inspection, owing to the ability of natural muons to penetrate into dense materials and the absence of artificial radiation. In this work, the material discrimination ability of muon scattering tomography is evaluated based on experiments at the Tsinghua University cosmic ray muon tomography facility,with four materials: flour(as drugs substitute), aluminum,steel, and lead. The features of the different materials could be discriminated with cluster analysis and classifiers based on support vector machine. The overall discrimination precisions for these four materials could reach 70, 95, and 99% with 1-, 5-, and 10-min-long measurement,respectively.展开更多
To mitigate consequences of core melting,an ex-vessel core catcher is investigated in this study.Instructions should be obeyed to cool down the corium caused by core melting.The corium destroys the reactor containment...To mitigate consequences of core melting,an ex-vessel core catcher is investigated in this study.Instructions should be obeyed to cool down the corium caused by core melting.The corium destroys the reactor containment and causes radioactive materials to be released into the environment if it does not cool down well.It is important to build a core catcher system for the reception,localization,and cool down of the molten corium during a severe accident resulting from core melting.In this study,the role of a core catcher in the VVER-1000/v528 reactor containment during a station black out(SBO)accident is evaluated using the MELCOR1.8.6 code.In addition,parametric analyses of the SBO for(i)SBO accidents with emergency core cooling system(ECCS)operation,and(ii)without ECCS operation are performed.Furthermore,thermal–hydraulic analyses in dry and wet cavities with/without water are conducted.The investigations include the reduction of gases resulting from molten–corium–concrete interactions(H_(2),CO,CO_(2)).Core melting,gas production,and the pressure/temperature in the reactor containment are assessed.Additionally,a full investigation pertaining to gas release(H_(2),CO,CO_(2))and the pressure/temperature of the core catcher is performed.Based on MELCOR simulations,a core cavity and a perimeter water channel are the best options for corium cooling and a lower radionuclide release.This simulation is also theoretically investigated and discussed herein.The simulation results show that the core catcher system in addition to an internal sacrificial material reduces the containment pressure from 689 to 580 kPa and the corresponding temperature from 394 to 380 K.Furthermore,it is observed that the amount of gases produced,particularly hydrogen,decreased from 1698 to 1235 kg.Moreover,the presence of supporting systems,including an ECCS with a core catcher,prolonged the core melting time from 16,430 to 28,630 s(in an SBO accident)and significantly decreased the gases produced.展开更多
To understand the physical and chemical characteristics, particle size distribution and sources of size-separated aerosols in Lhasa, which is located on the Tibetan Plateau(TP), six sizes of aerosol samples were colle...To understand the physical and chemical characteristics, particle size distribution and sources of size-separated aerosols in Lhasa, which is located on the Tibetan Plateau(TP), six sizes of aerosol samples were collected in Lhasa in 2014. Ca^(2+), NH_4^+, NO_3^-,SO_4^(2-)and Cl-were the dominant ions. The ratio of cation equivalents(CE) to anion equivalents(AE) for each particle size segment indicated that the atmospheric aerosols in Lhasa were alkaline. SO_4^(2-)and NO_3^-could be neutralized by Ca^(2+), but could not be neutralized by NH_4^+, according to the [NH_4^+]/[NO_3^-+ SO_4^(2-)] and [Ca^(2+)]/[NO_3^-+ SO_4^(2-)] ratios. Mobile sources were dominant in PM_(0.95-1.5),PM_(1.5-3) and PM_(3-7.2), while stationary sources were dominant in the other three size fractions according to the [NO_3^-]/[SO_4^(2-)] ratios. The particle size distribution of all watersoluble ions during monsoon and non-monsoon periods was characterized by a bimodal distribution due to the different sources and formation mechanisms, and it was revealed that different ions had different sources in different seasons and different particle size segments by combining particle size distribution with correlation analysis. Source analysis of aerosols in Lhasa was performed using the Principal component analysis(PCA) for the first time, which revealed that combustion sources, motor vehicle exhaust, photochemical reaction sources and various types of dust were the main sources of Lhasa aerosols.Furthermore, Lhasa's air quality was also affected by long-distance transmission, expressed as pollutants from South Asia and West Asia, which were transmitted to Lhasa according to backward trajectory analysis.展开更多
Modification of the surface properties of polyethylene （PE） films is studied using air dielectric barrier discharge at atmospheric pressure. The treated samples are examined by Water contact angle measurements, Four...Modification of the surface properties of polyethylene （PE） films is studied using air dielectric barrier discharge at atmospheric pressure. The treated samples are examined by Water contact angle measurements, Fourier transform infrared attenuated total reflection spectroscopy （FTIR-ATR）, X-ray photoelectron spectroscopy （XPS） and scanning electron microscopy （SEM）. With the increase in treating time, the water contact angle changes from 93.2° before treatment to a minimum of 53.3° after a treatment for 50 s. Both ATR and XPS results show some oxidized species are introduced into the sample surface by the plasma treatment and the tendency of the water contact angle with the treating time is the same as that of oxygen concentration on the treated sample surface. SEM result shows the surface roughness of PE samples increases with the treatment time increasing.展开更多
Corrosion degradation is detrimental to metal structures as it shortens their lifetime and leads to huge economic losses and unexpected disasters.Therefore,the detection and monitoring of corrosion degradation is of g...Corrosion degradation is detrimental to metal structures as it shortens their lifetime and leads to huge economic losses and unexpected disasters.Therefore,the detection and monitoring of corrosion degradation is of great importance.Herein,we briefly review the state-of-the-art electrochemical methods,instrumentation(based on virtual instrumentation),and advanced sensor/probes that are used in the field for the assessment of corrosion damage.Typical corrosion monitoring results,some of which have been obtained at Tianjin University in the past 30 years,for metallic materials and organic coating/metal systems in atmospheric,marine,and soil conditions in the field are presented.Detection methods,data analysis,and theoretical and mathematical models regarding each corrosion system are discussed,and the challenges,problems and possible solutions for each case are suggested.Lastly,future developments,such as wireless,intelligent,and automatic electrochemical measurement,that will augment the present electrochemical methods of evaluating corrosion degradation are summarized.展开更多
In the present work, an experimental study of bubbly two-phase flow in a rectangular bubble column was performed using two ultrasonic array sensors, which can measure the instantaneous velocity of gas bubbles on multi...In the present work, an experimental study of bubbly two-phase flow in a rectangular bubble column was performed using two ultrasonic array sensors, which can measure the instantaneous velocity of gas bubbles on multiple measurement lines. After the sound pressure distribution of sensors had been evaluated with a needle hydrophone technique, the array sensors were applied to two-phase bubble col- umn, To assess the accuracy of the measurement system with array sensors for one and two-dimensional velocity, a simultaneous measurement was performed with an optical measurement technique called particle image velocimetry （PIV）. Experimental results showed that accuracy of the measurement system with array sensors is under 10% for one-dimensional velocity profile measurement compared with PIV technique. The accuracy of the system was estimated to be under 20% along the mean flow direction in the case of two-dimensional vector mapping.展开更多
文摘The results of an accident analysis for the loss of offsite power(LOOP)scenario in a reference Bushehr-1 VVER-1000/V446 nuclear power plant(NPP)are presented in this paper.This study attempted to provide a better analysis of LOOP accident management by integrating deterministic and probabilistic approaches.The RELAP5 code was used to investigate the occurrence of specific thermal–hydraulic phenomena.The probabilistic safety assessment of the LOOP accident is presented using the SAPHIRE software.LOOP accident data were extracted from the Bushehr NPP final safety analysis reports and probabilistic safety analysis reports.A deterministic approach was used to reduce the core damage frequency in the probabilistic analysis of LOOP accidents.The probabilistic approach was used to better observe the philosophy of defense in depth and safety margins in the deterministic analysis of the LOOP accident.The results show that the integration of the two approaches in LOOP accident investigations improved accident control.
文摘A burnup calculation was performed to analyze the Apr`es ORIENT process, which aims to create highlyvaluable elements from fission products separated from spent nuclear fuels. The basic idea is to use nuclear transmutation induced by a neutron capture reaction followed by a β-decay, thus changing the atomic number Z of a target element in fission products by 1 unit. LWR(PWR) and FBR(MONJU) were considered as the transmutation devices. High rates of creation were obtained in some cases of platinum group metals(44Ru by FBR,46 Pd by LWR) and rare earth(64Gd by LWR,66 Dy by FBR). Therefore, systems based on LWR and FBR have their own advantages depending on target elements. Furthermore, it was found that creation rates of even Z(= Z + 1) elements from odd Z ones were higher than the opposite cases. This creation rate of an element was interpreted in terms of "average 1-group neutron capture cross section of the corresponding target element σc Z defined in this work. General trends of the creation rate of an even(odd) Z element from the corresponding odd(even) Z one were found to be proportional to the 0.78th(0.63th) power of σc Z, however with noticeable dispersion. The difference in the powers in the above analysis was explained by the difference in the number of stable isotopes caused by the even-odd effect of Z.
基金supported by the National Natural Science Foundation of China (No.22176067).
文摘The treatment and disposal of radioactive waste are presently facing great challenges.Spent ion exchange resins have become a focus of attention due to their high production and serious environmental risks.In this paper,a simplified model of cationic exchange resin is proposed,and the degradation processes of cationic resin monomer initiated by hydroxyl radicals(·OH)are clarified by combining statistical molecular fragmentation(SMF)model and density functional theory(DFT)calculations.The prediction of active sites indicates that the S-O bonds and the C-S bond of the sulfonic group are more likely to react during the degradation.The meta-position of the sulfonic group on the benzene ring is the most active site,and the benzene ring without the sulfonic group has a certain reactivity.The C11-C14 and C17-C20 bonds,on the carbon skeleton,are the most easily broken.It is also found that dihydroxy addition and elimination reactions play a major role in the process of desulfonation,carbon skeleton cleavage and benzene ring separation.The decomposition mechanisms found through the combination of physical models and chemical calculations,provide theoretical guidance for the treatment of complex polycyclic aromatic hydrocarbons.
基金supported by the National Science Foundation under Grant No.CMMI-1762190The research was performed in part in the Nebraska Nanoscale Facility:National Nanotechnology Coordinated Infrastructure and the Nebraska Center for Materials and Nanoscience (and/or NERCF),which are supported by the National Science Foundation under Award ECCS:2025298+1 种基金the Nebraska Research Initiativesupported by the U.S.Department of Energy,Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07-051D14517 as part of a Nuclear Science User Facilities experiment。
文摘W-based WTaVCr refractory high entropy alloys (RHEA) may be novel and promising candidate materials for plasma facing components in the first wall and diverter in fusion reactors. This alloy has been developed by a powder metallurgy process combining mechanical alloying and spark plasma sintering (SPS). The SPSed samples contained two phases, in which the matrix is RHEA with a body-centered cubic structure, while the oxide phase was most likely Ta2VO6through a combined analysis of X-ray diffraction (XRD),energy-dispersive spectroscopy (EDS), and selected area electron diffraction (SAED). The higher oxygen affinity of Ta and V may explain the preferential formation of their oxide phases based on thermodynamic calculations. Electron backscatter diffraction (EBSD) revealed an average grain size of 6.2μm. WTaVCr RHEA showed a peak compressive strength of 2997 MPa at room temperature and much higher micro-and nano-hardness than W and other W-based RHEAs in the literature. Their high Rockwell hardness can be retained to at least 1000°C.
基金supported by the Russell Family Foundation Grant for research on High Level Waste Packages and Dry Casksthe Department of Nuclear Engineering at North Carolina State University。
文摘The shielding and corrosion properties of the Alloy 709 advanced austenitic stainless steel have been investigated as a candidate canister material in spent fuel dry casks.The results revealed that the experimental and computational data of the linear and mass attenuation coefficients of the alloy are in good agreement,in which the attenuation coefficient values decreased with increasing photon energy.Alloy 709 was shown to exhibit the highest linear attenuation coefficient against gamma rays when compared to 304 and 316 stainless steels.On the other hand,Alloy 709 exhibited no considerable weight change over a 69-day period in circulating salt brines corrosion testing,while it showed an exponential increase of corrosion current density with temperature in acidic and basic corrosive solutions during electrochemical polarization corrosion testing.Furthermore,Alloy 709 was the least corroded steel compared to other austenitic stainless steels in both acidic and basic solutions.The optimistic results of the shielding and corrosion properties of Alloy 709 due to its chemical composition,suggest utilizing it as a canister material in spent nuclear fuel dry casks.
文摘Small modular reactors (SMRs) offer simple, standardized, and safe modular designs for new nuclear reactor construction. They are factory built, requiring smaller initial capital investment and facilitating shorter construction times. SMRs also promise competitive economy when compared with the current reactor fleet. Construction cost of a majority of the projects, which are mostly in their design stages, is not publicly available, but variable costs can be determined from fuel enrichment, average burn-up, and plant thermal efficiency, which are public parameters for many near-term SMR projects. The fuel cost of electricity generation for selected SMRs and large reactors is simulated, including calculation of optimal tails assay in the uranium enrichment process. The results are compared between one another and with current generation large reactor designs providing a rough comparison of the long-term economics of a new nuclear reactor project. SMRs are predicted to have higher fuel costs than large reactors. Particularly, integral pressurized water reactors (iPWRs) are shown to have from 15% to 70% higher fuel costs than large light water reactors using 2014 nuclear fuels market data. Fuel cost sensitivities to reactor design parameters are presented.
文摘This paper investigates long-term energy strategy compatible with significant reduction of world carbon dioxide （CO2） emissions, employing a long-term global energy model, Dynamic New Earth 21 （called DNE21）. The model seeks the optimal energy mix from 2000 to 2100 that minimizes the world total energy system cost under various kinds of energy and technological constraints, such as energy resource constraints, energy supply and demand balance constraints, and CO2 emissions constraints. This paper discusses the results of primary energy supply, power generation mix, CO2 emission, CCS （carbon capture and storage） and total system costs for six regions including world as a whole. To evaluate viable pathways forward for implementation of sustainable energy strategies, nuclear power generation is a viable source of clean and green energy to mitigate the CO2 emissions. Present research shows simulation results in two cases consisting of no CO2 regulation case （base case） and CO2 REG case （regulation case） which halves the world CO2 emissions by the year 2050. Main findings of this research describe that renewable and nuclear power generation will contribute significantly to mitigate the CO2 emission worldwide.
文摘Dose estimation and quality control in computed tomography (CT) scanners are useful in controlling the dose of radiation given to patients while tests are carried out. The study was performed in a 16-slice Computed Tomography (CT) system of LightSpeed RT16 Xtra CT scanner. Quality control was done using a vendor-provided QA Phantom, and the six aspects of image quality were measured. For CT dosimetry, Computed Tomography Dose index volume (CTDIvol) was performed using Computed Tomography Dose Index (CTDI) Phantom. CTDI Phantom consists of three parts: Pediatric Head, Adult Head, and Adult Body Phantom. A 10 cm long pencil ion chamber DCT-10 was used to measure the dose at different positions inside the CTDI Phantom. Data were collected using MagicMax Universal software. For dose estimation of the CTDIvol Report of AAPM Task Group, 96 and 111 formalisms were used. For Pediatric Head, Adult Head, and Adult Body Phantom the measured CIDIvol was 61.04 mGy, 48.11 mGy, and 18.08 mGy respectively. The study has shown deviations of 7%, 15%, and 19% between estimated and console-displayed doses for Pediatric Head, Adult Head, and Adult Body scan techniques respectively. The six aspects of image quality measured by QA Phantom were found to be compatible with the specifications of the machine and CTDIvol measured by CTDI Phantom were found within a tolerance limit of ±20%. Hence, the QC and dosimetry of the mentioned machine are within the limit.
基金funding support by the Changsha Natural Science Foundation(grant no.kq2208023)National Natural Scientific Foundation of China(grant no.12074113).
文摘Transition metal(oxy)hydroxides are potential oxygen evolution reaction(OER)electrocatalysts;however,simultaneously modulating multiple factors to enhance their performance is a grand challenge.Here,we report an incorporating heteroatom strategy via one-step hydrothermal approach to adjust more than one factor of Mn-doped NiFe(oxy)hydroxide(Mn-NiFeOOH/LDH)heterojunction.Mn doping regulates heterojunction morphology(reducing nanoparticles and becoming thinner and denser nanosheets),Ni/Fe ratio and valence states(Ni^(2+),Ni^(3+),and Ni^(3+Δ))of Ni ions.The former could effectively increase surface active sites,and the latter two reduce the content of Fe in the Mnx-NiFeOOH/LDH heterojunction,en-abling more Ni^(2+)convert to Ni^(3+/3+Δ)that have higher intrinsic OER activity.As a result,the first-rank Mn-NiFeOOH/LDH with ultra-low overpotential of 185 mV@20 mA cm^(-2) and 296 mV@500 mA cm^(-2),and the improved OER performance are outdo to those of commercial RuO_(2) catalyst for OER.Moreover,the Mn-NiFeOOH/LDH affords the earliest initial potential(1.392 V vs.RHE),corresponds to a recorded low overpotential(162 mV).Based on the density functional theory(DFT),Mn dopants can alter intermedi-ate adsorption energy and effectively decrease∗OOH’s energy barrier.This research exhibits a feasible strategy to design low cost electrocatalysts and provide new possibilities for future industrialization.
基金supported by Huck Institutes of the Life Sciences at Penn State University through the Huck Innovative and Transformational Seed Grant(HITS).
文摘Advancing 3D magnesium(Mg)development beyond current limitations requires controlling Mg alloy degradation in pre-designed,low-dimension architectures.This study reveals a mechanistic switch in the corrosion behavior of Mg alloy(3.6%Al,0.8%Zn)diamond lattice structures,induced by plasma nanosynthesis(400 eV Ar^(+)ions,fluence 1×10^(17) ions/cm^(2)).Plasma treatment of the Mg alloy increases surface Mg from 1.5%to 14.5%,enhances carbonate formation,and generates a nanostructured surface with a Mg carbonate layer over an oxide/hydroxide layer.In vitro and in vivo analyses over 8 wk demonstrate how this treatment fundamentally alters the degradation process and stability of these 3D architectures.While untreated samples initially formed a protective film that subsequently diminished,DPNS-treated samples demonstrated an inverse corrosion behavior.X-ray photoelectron spectroscopy(XPS)and electrochemical impedance spectroscopy(EIS)confirmed the presence of a stable,protective layer composed of magnesium oxide,magnesium hydroxide,and magnesium carbonate on the DPNS-treated surfaces.After 14 days,the DPNS-treated sample exhibited a more positive corrosion potential(-0.69 V versus-1.36 V)and a marginally lower current density(0.73 mA/cm^(2)compared to 0.75 mA/c^(2))relative to the control.This protective layer,combined with modified surface topology,initiated a core-to-periphery degradation pattern that maintained structural integrity for up to 8 wk post-implantation.These findings support the conclusion that the DPNS-treated scaffold demonstrates sustained improved corrosion resistance over time compared to the untreated control.Micro-CT revealed plasma-treated samples retained larger struts(504.9±95.3μm at 8 wk)and formed larger H_(2) pockets extending 14.2 mm from the implant center,versus 4.9 mm in controls.This corrosion behavior switch enhances stability but risks pore clogging,offering insights for tailoring Mg alloy degradation and H_(2) evolution in 3D architectures for biomedical applications.
基金supported by the U.S.Department of EnergyOffice of Science+5 种基金Fusion Energy Sciences Programunder Contract No.DE-AC05-00OR22725 with UT-BattelleLLCfinancial support from the US Department of EnergyOffice of Fusion Energy Science under grant DOE-DE-SC000661 at The University of Tennessee-KnoxvilleJLW and HCM were funded by the National Institute of Standards and Technology。
文摘Tungsten(W)is the leading plasma-facing candidate material for the International Thermonuclear Experimental Reactor and next-generation fusion reactors.The impact of synergistic helium(He),irradiation-induced microstructural changes,and the corresponding thermal-mechanical property degradation of W are critically important but are not well understood yet.Predicting the performance of W in fusion environments requires understanding the fundamentals of He-defect interactions and the resultant He bubble nucleation and growth in W.In this study,He retention in helium-ion-implanted W was assessed using neutron depth profiling(NDP),laser ablation mass spectrometry(LAMS),and thermal desorption spectroscopy(TDS)following 10 keV room-temperature He implantation at various fluences.These three experimental techniques enabled the determination of the He depth profile and retention in He-implanted W.A cluster dynamics model based on the diffusion-reaction rate theory was applied to interpret the experimental data.The model successfully predicted the He spatial depth-dependent profile in He-implanted W,which was in good agreement with the LAMS measurements.The model also successfully captured the major features of the He desorption spectra observed in the THDS measurements.The NDP quantified total He concentration values for the samples;they were similar to those estimated by LAMS.However,the depth profiles from NDP and LAMS were not comparable due to several factors.The combination of modeling and experimentation enabled the identification of possible trapping sites for He in W and the evolution of He-defect clusters during the TDS thermal annealing process.
基金supported by the National Natural Science Foundation of China (Nos. 11605271, 51471044, 51525401, 51771201 and 51401208)Support Plan for Innovation of High-level Talents (Top and Leading Talents, 2015R013)Support Plan for Innovation of High-level Talents (Youth Technology Stars, 2016RQ005)
文摘Recently, high-entropy alloys(HEAs) or multi-principal-element alloys with unprecedented physical,chemical, and mechanical properties, have been considered as candidate materials used in advanced reactors due to their promising irradiation resistant behavior. Here, we report a new single-phase bodycentered cubic(BCC) structured Ti_2 ZrHfV_(0.5)Mo_(0.2) HEA possessing excellent irradiation resistance, i.e.,scarcely irradiation hardening and abnormal lattice constant reduction after helium-ion irradiation,which is completely different from conventional alloys. This is the first time to report the abnormal XRD phenomenon of metallic alloys and almost no hardening after irradiation. These excellent properties make it to be a potential candidate material used as core components in next-generation nuclear reactors. The particular irradiation tolerance derives from high density lattice vacancies/defects.
文摘The phenomenon of direct-contact condensation,used in steam driven jet injectors,nuclear reactor emergency core cooling systems and direct-contact heat exchangers,was investigated computationally by introducing a thermal equilibrium model for direct-contact condensation of steam in subcooled water.The condensation model presented was a two resistance model which takes care of the heat transfer process on both sides of the interface and uses a variable steam bubble diameter.The injection of supersonic steam jet in subcooled water tank was simulated using the Euler-Euler multiphase flow model of Fluent 6.3 code with the condensation model incorporated. The findings of the computational fluid dynamics（CFD） simulations were compared with the published experimental data and fairly good agreement was observed between the two,thus validating the condensation model.The results of CFD simulations for dimensionless penetration length of steam plume varies from 2.73-7.33,while the condensation heat transfer coefficient varies from 0.75-0.917 MW·（m ^2 ·K）^ -1 for water temperature in the range of 293-343 K.
基金supported by The National Natural Science Foundation of China under Grant No.11390362 and No. 11221202
文摘This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at three positions: contact detonation in the center, contact detonation above the web and close-in detonation in the center. The external and internal breach parameters of the panels were evaluated by measuring the diameter of the ejection crater, spalling crater and breach hole created by the charge detonation. The experimental results were compared to predict values obtained by the analytical models proposed by McVay, Morishita and Remennikov. A modified breach with crater limit line and breach without crater limit line were put forward based on the experimental results. The maximum cross-sectional destruction area ratio(MCDAR) values were used to evaluate the damage degree. The maximum value of MCDAR reached 0.331 corresponding to the C5 experimental condition, of which explosion occurred above the web.
文摘Muon scattering tomography is believed to be a promising technique for cargo container inspection, owing to the ability of natural muons to penetrate into dense materials and the absence of artificial radiation. In this work, the material discrimination ability of muon scattering tomography is evaluated based on experiments at the Tsinghua University cosmic ray muon tomography facility,with four materials: flour(as drugs substitute), aluminum,steel, and lead. The features of the different materials could be discriminated with cluster analysis and classifiers based on support vector machine. The overall discrimination precisions for these four materials could reach 70, 95, and 99% with 1-, 5-, and 10-min-long measurement,respectively.
文摘To mitigate consequences of core melting,an ex-vessel core catcher is investigated in this study.Instructions should be obeyed to cool down the corium caused by core melting.The corium destroys the reactor containment and causes radioactive materials to be released into the environment if it does not cool down well.It is important to build a core catcher system for the reception,localization,and cool down of the molten corium during a severe accident resulting from core melting.In this study,the role of a core catcher in the VVER-1000/v528 reactor containment during a station black out(SBO)accident is evaluated using the MELCOR1.8.6 code.In addition,parametric analyses of the SBO for(i)SBO accidents with emergency core cooling system(ECCS)operation,and(ii)without ECCS operation are performed.Furthermore,thermal–hydraulic analyses in dry and wet cavities with/without water are conducted.The investigations include the reduction of gases resulting from molten–corium–concrete interactions(H_(2),CO,CO_(2)).Core melting,gas production,and the pressure/temperature in the reactor containment are assessed.Additionally,a full investigation pertaining to gas release(H_(2),CO,CO_(2))and the pressure/temperature of the core catcher is performed.Based on MELCOR simulations,a core cavity and a perimeter water channel are the best options for corium cooling and a lower radionuclide release.This simulation is also theoretically investigated and discussed herein.The simulation results show that the core catcher system in addition to an internal sacrificial material reduces the containment pressure from 689 to 580 kPa and the corresponding temperature from 394 to 380 K.Furthermore,it is observed that the amount of gases produced,particularly hydrogen,decreased from 1698 to 1235 kg.Moreover,the presence of supporting systems,including an ECCS with a core catcher,prolonged the core melting time from 16,430 to 28,630 s(in an SBO accident)and significantly decreased the gases produced.
基金supported by the National Natural Science Foundation of China(Nos.11775180,11475082 and 41603096)the Graduate Student Research Innovation Project of Hunan Province(No.2014SCX03)the General Program of the Hunan,Provincial Education Department(No.17C1353)
文摘To understand the physical and chemical characteristics, particle size distribution and sources of size-separated aerosols in Lhasa, which is located on the Tibetan Plateau(TP), six sizes of aerosol samples were collected in Lhasa in 2014. Ca^(2+), NH_4^+, NO_3^-,SO_4^(2-)and Cl-were the dominant ions. The ratio of cation equivalents(CE) to anion equivalents(AE) for each particle size segment indicated that the atmospheric aerosols in Lhasa were alkaline. SO_4^(2-)and NO_3^-could be neutralized by Ca^(2+), but could not be neutralized by NH_4^+, according to the [NH_4^+]/[NO_3^-+ SO_4^(2-)] and [Ca^(2+)]/[NO_3^-+ SO_4^(2-)] ratios. Mobile sources were dominant in PM_(0.95-1.5),PM_(1.5-3) and PM_(3-7.2), while stationary sources were dominant in the other three size fractions according to the [NO_3^-]/[SO_4^(2-)] ratios. The particle size distribution of all watersoluble ions during monsoon and non-monsoon periods was characterized by a bimodal distribution due to the different sources and formation mechanisms, and it was revealed that different ions had different sources in different seasons and different particle size segments by combining particle size distribution with correlation analysis. Source analysis of aerosols in Lhasa was performed using the Principal component analysis(PCA) for the first time, which revealed that combustion sources, motor vehicle exhaust, photochemical reaction sources and various types of dust were the main sources of Lhasa aerosols.Furthermore, Lhasa's air quality was also affected by long-distance transmission, expressed as pollutants from South Asia and West Asia, which were transmitted to Lhasa according to backward trajectory analysis.
基金the Science Development Foundation of the Engineering and Technical College of Chengdu University of Technology of China(Nos.C122007025,C122007018)
文摘Modification of the surface properties of polyethylene （PE） films is studied using air dielectric barrier discharge at atmospheric pressure. The treated samples are examined by Water contact angle measurements, Fourier transform infrared attenuated total reflection spectroscopy （FTIR-ATR）, X-ray photoelectron spectroscopy （XPS） and scanning electron microscopy （SEM）. With the increase in treating time, the water contact angle changes from 93.2° before treatment to a minimum of 53.3° after a treatment for 50 s. Both ATR and XPS results show some oxidized species are introduced into the sample surface by the plasma treatment and the tendency of the water contact angle with the treating time is the same as that of oxygen concentration on the treated sample surface. SEM result shows the surface roughness of PE samples increases with the treatment time increasing.
基金the National Natural Science Foundation of China(Nos.52031007,52171077)partial support of his contribution to the work by the University of California at Berkeley。
文摘Corrosion degradation is detrimental to metal structures as it shortens their lifetime and leads to huge economic losses and unexpected disasters.Therefore,the detection and monitoring of corrosion degradation is of great importance.Herein,we briefly review the state-of-the-art electrochemical methods,instrumentation(based on virtual instrumentation),and advanced sensor/probes that are used in the field for the assessment of corrosion damage.Typical corrosion monitoring results,some of which have been obtained at Tianjin University in the past 30 years,for metallic materials and organic coating/metal systems in atmospheric,marine,and soil conditions in the field are presented.Detection methods,data analysis,and theoretical and mathematical models regarding each corrosion system are discussed,and the challenges,problems and possible solutions for each case are suggested.Lastly,future developments,such as wireless,intelligent,and automatic electrochemical measurement,that will augment the present electrochemical methods of evaluating corrosion degradation are summarized.
文摘In the present work, an experimental study of bubbly two-phase flow in a rectangular bubble column was performed using two ultrasonic array sensors, which can measure the instantaneous velocity of gas bubbles on multiple measurement lines. After the sound pressure distribution of sensors had been evaluated with a needle hydrophone technique, the array sensors were applied to two-phase bubble col- umn, To assess the accuracy of the measurement system with array sensors for one and two-dimensional velocity, a simultaneous measurement was performed with an optical measurement technique called particle image velocimetry （PIV）. Experimental results showed that accuracy of the measurement system with array sensors is under 10% for one-dimensional velocity profile measurement compared with PIV technique. The accuracy of the system was estimated to be under 20% along the mean flow direction in the case of two-dimensional vector mapping.
