Monte-Carlo Simulation on Neutron Instruments at CARR

The design of high resolution neutron powder diffractometer(HRPD) and two cold neutron guides(CNGs) to be built at China advanced research reactor(CARR) are studied by Monte-Carlo simulation technique.The HRPD instrument is desiged to have a minimum resolution of 0.2% and neutron fluence rate of greater than 106 cm-2 ·s-1 at sample position. The resolution curves, neutron fluence rate and effective neutron beam size at sample position are given. Differences in resolutions and intensity between the     

Existence of the fifth unstable nuclide series

The production of derived nuclides by the reaction of ^238U with constant nuclear reactor neutron flux for long time is theoretically described.The concentration of each derived nuclide is zero at the beginning.then increases gradually and approaches a saturated value at a certain irradiation time.The whole system(including the parent nuclide ^238U and all its derived nuclides)will be in a state of equilibrium.Upon the reaction with neutron flux,the whole system decreases its concentration at the same rate as 238U.It constitutes actually a new type of unstable nuclide series which is in owrk only in the presence of reactor neutron flux.It has been found that the amount of materials consumed by neutron flux reaction is almost converted entrely to fission product.This peculiar property is quite different from the well known four radioactive series,so that it is named the fifth unstable nuclide series.     

Displacement damage cross section and mechanical properties calculation of an Es-Salam research reactor aluminum vessel

Nuclear facility aging is one of the biggest problems encountered in nuclear engineering. Radiation damage is among one of the aging causes. This kind of damage is an important factor of mechanical properties deterioration. The interest of this study is on the Es-Salam research reactor aluminum vessel aging due to neutron radiation. Monte Carlo(MC) simulations were performed by MCNP6 and SRIM codes to estimate the defects created by neutrons in the vessel. MC simulations by MCNP6 have been performed to determine the distribution of neutron fluence and primary knock-on atom(PKA) creation. Considering our boundary conditions of the calculations, the helium and hydrogen gas production in the model at a normalized total neutron flux of 6.62×10~(12) n/cm~2 s were determined to be 2.86 × 10~8 and 1.33 × 10~9 atoms/cm~3 s,respectively. The SRIM code was used for the simulation of defects creation(vacancies, voids) in the aluminum alloy of the Es-Salam vessel(EsAl) by helium and hydrogen with an approximate energy of 11 MeV each.The coupling between the two codes is based upon postprocessing of the particle track(PTRAC) output file generated by the MCNP6. A small program based on the Mat Lab language is performed to condition the output file MCNP6 in the format of a SRIM input file. The concentration of silicon was determined for the vessel by the calculation of the total rate of ~(27)Al(n,γ)~(28)Si reaction. The DPA(displacement per atom) was calculated in SRIM according to R.E. Stoller recommendations; the calculated value is 0.02 at a fast neutron fluence 1.89 × 10~(19) n/cm~2.RCC-MRx standard for 6061-T6 aluminum was used for the simulation of the evolution of mechanical properties for high fluence. The calculated values of nuclear parameters and DPA obtained were in agreement with the experimental results from the Oak Ridge High Flux Isotope Reactor(HFIR) reported by Farrell and coworkers.     

Preliminary Design and Analysis of the DC Reactor for the ITER Converter

The DC reactor is an important piece of equipment for restraining loop and ripple currents in the international thermonuclear experimental reactor （ITER） converter power supply system. As the reactor is operated at a steady state of 27.5 kA and needs to withstand a peak current of 175 kA, so the design of the DC reactor used in the ITER converter power supply system is necessary. A new water-cooling dry-type air-core reactor is designed in this work. The detailed structural parameters are calculated by theoretical formulas, and then the structure is optimized by electromagnetic simulation with ANSYS. Finally, thermal and dynamic stability analyses are performed to verify the temperature and stress at a rated current of 27.5 kA and pulsed current of 175 kA. The analysis results show that the temperature and stress meet the requirements of the ITER converter power supply system.     

Core cooling in pressurized-water reactor during water injection

In this paper,the reactor core cooling and its melt progression terminating is evaluated,and the initiation criterion for reactor cavity flooding during water injection is determined.The core cooling in pressurized-water reactor of severe accident is simulated with the thermal hydraulic and severe accident code of SCDAP/RELAP5.The results show that the core melt progression is terminated by water injection,before the core debris has formed at bottom of core,and the initiation of reactor cavity flooding is indicated by the core exit temperature.     

DBD coupled with MnOx/γ-Al2O3 catalysts for the degradation of chlorobenzene

This paper investigates the degradation of chlorobenzene by dielectric barrier discharge(DBD)coupled with MnOx/γ-Al2O3 catalysts.MnOx/γ-Al2O3 catalysts were prepared using the impregnation method and were characterized in detail by N2 adsorption/desorption,x-ray diffraction and x-ray photoelectron spectroscopy.Compared with the single DBD reactor,the coupled reactor has a better performance on the removal rate of chlorobenzene,the selectivity of COx,and the inhibition of ozone production,especially at low discharge voltages.The degradation rate of chlorobenzene and selectivity of COx can reach 96.3%and 53.0%,respectively,at the specific energy density of 1350 J l-1.Moreover,the ozone concentration produced by the discharge is significantly reduced because the MnOx/Al2O3 catalysts contribute to the decomposition of ozone to form oxygen atoms for the oxidation of chlorobenzene.In addition,based on analysis of the byproducts,the decomposition mechanism of chlorobenzene in the coupled reactor is also discussed.     

Discharge Simulation and Fabrication Process of an Aluminum Electrode and an Alumina Layer in AC-PDP

A larger space PDP cell with patterned aluminum as the addressing electrode and alumina as the dielectric layer was proposed. The aluminum electrode and the alumina dielectric layer formed on the aluminum electrode were prepared separately by magnetron sputtering and anodic oxidation for plasma display panel. The properties of the aluminum electrode and the alumina dielectric layer were tested and can meet the demand of PDP application. The resistivity of the aluminum electrode is about 5×10 8 ·m, the voltage withstanding of the alumina dielectric layer exceeds 100 V/μm and the relative permittivity is about 3.5 at 1 MHz. With this structure, the manufacturing cost of PDP could be cut and the addressing discharge formative delay is reduced by 0.67%, which is proved by PIC-MCC simulation.     

Degradation of Dye Wastewater by ns-Pulse DBD Plasma

Two plasma reactors have been developed and used to degrade dye wastewater agents.The configuration of one plasma reactor is a comb-like extendable unit module consisting of 5 electrodes covered with a quartz tube and the other one is an array reactor which is extended from the unit module.The decomposition of wastewater by ns pulse dielectric barrier discharge(DBD) plasma have been carried out by atomizing the dyeing solutions into the reactors.During experiments,the indigo carmine has been treated as the waste agent.The measurements of UV-VIS absorption spectroscopy and the chemical oxygen demand(COD) are carried out to demonstrate the decomposition efect on the wastewater.It shows that the decoloration rate of 99% and the COD degradation rate of 65% are achieved with 15 min treatment in the unit reactor.The efect of electrical parameters on degradation has been studied in detail.Results from the array reactor indicate that it has a better degradation efect than the unit one.It can not only totally remove the chromogenic bond of the indigo carmine solution,but also efectively degrade unsaturated bonds.The decoloration rate reaches 99% after 10 min treatment,the decomposition rate of the unsaturated bond reaches 83% after 60 min treatment,and the COD degradation rate is nearly 74%.     

Non—Conventional Plasma Assisted Catalysts for Diesel Exhaust Treatment：A Case Study

This paper reports the application of pulse discharges along with catalysts in treating the exhaust gas at higher temperatures.In the present work a plasma reactor,filled with catalysts,called as plasma catalytic reactor,is studied for removal of oxides of nitrogen,total hydrocarbons and carbon monoxide.The experiments are conducted on an actual diesel engine exhaust at no-load and at different temperatures starting from room temperature to 300℃.The removal efficiencies of these pollutants are studied.The experiments are carried out with both conventional and non-conventional catalysts.The idea to explore the pollutant removal efficiency characteristics by non-conventional catalysts.The efficiency results are compared with that of conventional catalysts.The experiments are carried out at a constant pulse repetition rate of 120pps.Both pellet and honeycomb type catalysts are used in the study.     

Specifications of nanosecond laser ablation with solid targets,aluminum, silicon rubber,and polymethylmethacrylate (PMMA)

The ablation parameters such as threshold fluence, etch depth, ablation rate and the effect of material targets were investigated under the interaction of laser pulse with low intensity. The parameters of the laser system are: laser pulse energy in the range of 110–140 m J, wavelength1064 nm and pulse duration 20 ns. By macroscopic estimation of the outward images of the ablation and data obtained, we can conclude that the photothermal and photoionization processes have more influence for aluminum ablation. In contrast, for polymer samples, from the macroscopic observation of the border pattern at the irradiated spot, and also the data obtained from the experiment results, we deduce that both chemical change due to heating and photochemical dissociation were effective mechanisms of ablation. However, concerning the two polymer samples, apart from considering the same theoretical ablation model, it is conceived that the photomehanical specifications of PMMA are involved in the ablation parameters. The threshold fluence for an ablation rate of 30 laser shots were obtained as 12.4, 24.64, and 11.71 J cm~(-2), for aluminum, silicon rubber and polymethylmethacrylate(PMMA) respectively.The ablation rate is exponentially decreased by the laser-shot number, especially for aluminum.Furthermore, the etch depth after 30 laser shots was measured as 180, 630 and 870 μm, for aluminum, silicon rubber and PMMA, respectively.     

Fabrication and basic characterization of silicon nitride ceramics as an inert matrix

Silicon nitride ceramics containing cerium as a simulating element of americium were fabricated to clarify proper sintering conditions. Basic properties of sintered specimens were evaluated for utilization to an inert matrix. Commercial powders of silicon nitride and cerium dioxide (16 or 24.6 wt%), and a powder of aluminum oxide or zirconium oxide as a sintering additive (5 wt%) for some specimens were mixed by ball milling in ethanol. Small amounts of stearic acid as a lubricant were also added. The mixed powder was uniaxially pressed into cylindrical pellets. Then, the pellets were embedded in a packing powder composed of 50 wt%-Si₃N₄ and 50 wt%-BN, and sintered at 2023 or 2073 K for 2 h in a 0.1 MPa N₂ atmosphere. Most of the sintered specimens had high densities (>95% TD). Sintered bodies consisted of columnar silicon nitride grains and grain-boundary phase. XRD analysis clarified that the grain-boundary phase contained crystalline compounds of cerium. The thermal conductivities of sintered specimens except for specimens containing aluminum oxide were about 40 W/m K at room temperature.     

Comparative research of plasma-assisted milling and traditional milling in synthesizing AlN

In this paper, traditional milling and discharge plasma-assisted milling are employed to synthesize aluminum nitride (AlN) powder at nanometer scale by milling the mixture of aluminum and lithium hydroxide monohydrate. AlN powders can be generated in traditional milling and plasma-assisted milling in an hour milling time. Differential thermal analysis curves show that the reaction temperature of the powders treated by plasma-assisted milling is lower than that of traditional milling. These results indicate that plasma-assisted milling has higher efficiency in the synthesis of AlN, getting smaller crystallite size and activating powder. Moreover, an optical emission spectrum is employed to demonstrate the active species in plasma. The different formation process of AlN in the two-milling process, and the promotion effects of plasma in the milling process are discussed.     

Comparative research of plasma-assisted milling and traditional milling in synthesizing AIN

In this paper,traditional milling and discharge plasma-assisted milling are employed to synthesize aluminum nitride (AlN) powder at nanometer scale by milling the mixture of aluminum and lithium hydroxide monohydrate.AlN powders can be generated in traditional milling and plasma-assisted milling in an hour milling time.Differential thermal analysis curves show that the reaction temperature of the powders treated by plasma-assisted milling is lower than that of traditional milling.These results indicate that plasma-assisted milling has higher efficiency in the synthesis of AlN,getting smaller crystallite size and activating powder.Moreover,an optical emission spectrum is employed to demonstrate the active species in plasma.The different formation process of AlN in the two-milling process,and the promotion effects of plasma in the milling process are discussed.     

Reduction of surface erosion caused by helium blistering in sintered beryllium and sintered aluminum powder

Studies have been conducted to find materials with microstructures which minimize the formation of blisters. A promising class of materials appears to be sintered metal powder with small average grain sizes and low atomic number Z. Studies of the surface erosion of sintered aluminum powder (SAP 895) and of aluminum held at 400°C due to blistering by 100-keV helium ions have been conducted, and the results are compared to those obtained earlier for room temperature irradiation. A significant reduction of the erosion rate in SAP 895 in comparison to annealed aluminum and SAP 930 is observed. In addition results of the blistering of sintered beryllium powder irradiated at room temperature and 600°C by 100-keV helium ions are given. These results show a reduction in erosion rate in both types of sintered beryllium as compared to the erosion rate in vacuum-cast beryllium for both room temperature and 600°C.     

氮化铀粉末合成工艺研究

氮化铀燃料制备的关键技术之一是纯度高、烧结活性好的氮化铀粉末合成工艺技术.本文开展了以三碳酸铀酰胺(AUC)流程制备的高活性氧化铀粉末和高纯度的碳黑为主要原材料,采用碳热还原-氮化反应合成氮化铀粉末的工艺研究,初步考察了碳铀摩尔比、反应气氛以及反应温度和时间等对合成产物成分的影响.实验结果表明,采用适当的碳铀摩尔比(2.3～2.4)以及反应制度可以制备出较高纯度的氮化铀粉末.     

Thermal conductivity degradation of ceramic materials due to low temperature, low dose neutron irradiation

The thermal conductivity degradation due to low-temperature neutron irradiation is studied and quantified in terms of thermal resistance terms. Neutron irradiation is assumed to have no effect on umklapp scattering. A theoretical model is presented to quantify the relative phonon-scattering effectiveness of the three dominant defect types produced by neutron irradiation: point defects, dislocation loops and voids. Several commercial ceramics have been irradiated with fission reactor fast neutrons at low temperatures to produce defects. Materials include silicon carbide, sapphire, polycrystalline alumina, aluminum nitride, silicon nitride, beryllium oxide, and a carbon fiber composite. The neutron dose corresponded to 0.001 and 0.01 displacements per atom (dpa) for a 60 °C irradiation and 0.01 and 0.1 dpa for a 300 °C irradiation. Substantial thermal conductivity degradation occurred in all of the materials except BeO following irradiation at 60 °C to a dose of only 0.001 dpa. The data are discussed in terms of the effective increase in thermal resistance caused by the different irradiation conditions. Evidence for significant point defect mobility during irradiation at 60 and 300 °C was obtained for all of the ceramics. The thermal stability of the radiation defects was investigated by isochronal annealing up to 1050 °C.     

Status of the Development and Production of Uranium–Plutonium Fuel for Fast Reactors

A comparative assessment is given of the status of the technology for producing uranium–plutonium oxide and nitride fuel and reactor tests and postreactor studies. The additional investigations of nitride fuel required to substantiate a possible reactor core design with such fuel are noted.     

快堆中不同核燃料类型的长寿期性能评价

建立了典型的快堆六角形栅元堆芯模型,研究了多种类型的燃料在快中子能谱辐照环境下经过较长时间辐照后的性能,对不同燃料堆芯在运行寿期末的乏燃料组成成分进行了分析.结果表明,在栅元结构完全一样且初始剩余反应性基本相同的情况下,燃料反应性损失从小到大的顺序是:金属燃料＜氮化物燃料＜碳化物燃料<氧化物燃料;在整个寿期中,使用Pu驱动的燃料比使用235U驱动的燃料反应性下降得慢;金属燃料寿期末乏燃料中按初始装载燃料质量平均后的超铀核素的质量最小,其他依次为氧化物<氮化物<碳化物;由于初始装载量的增多,使用Pu驱动的燃料寿期末乏燃料超铀核素的总量比使用235U驱动的燃料多,同时,乏燃料Pu中的易裂变同位素的份额比235U驱动燃料的少.从中子学角度考虑,UZr燃料是比较理想的长寿命快堆堆芯燃料类型.     

反应堆中心孔道辐照材料的中子与γ释热研究

反应堆辐照材料上中子与γ的释热率是该材料在堆中热工计算的重要输入参数.本文基于蒙特卡罗粒子输运程序(MCNP),计算了某堆首炉高热中子堆芯布置下,L12中心孔道中不同材料(水、T6061铝、单晶硅、不锈钢、锆合金)轴向的中子、γ释热率分布.计算结果表明,活性区轴向高度为0～1000 mm,中子与γ在材料上的最大释热率点...     

Experimental investigation of material chemical effects on emergency core cooling pump suction filter performance after loss of coolant accident

Integral tests of head loss through an emergency core cooling filter screen are conducted, simulating reactor building environmental conditions for 30 days after a loss of coolant accident. A test rig with five individual loops each of whose chamber is established to test chemical product formation and measure the head loss through a sample filter. The screen area at each chamber and the amounts of reactor building materials are scaled down according to specific plant condition. A series of tests have been performed to investigate the effects of calcium-silicate, reactor building spray, existence of calcium-silicate with tri-sodium phosphate (TSP), and composition of materials. The results showed that head loss across the chemical bed with even a small amount of calcium-silicate insulation instantaneously increased as soon as TSP was added to the test solution. Also, the head loss across the filter screen is strongly affected by spray duration and the head loss increase is rapid at the early stage, because of high dissolution and precipitation of aluminum and zinc. After passivation of aluminum and zinc by corrosion, the head loss increase is much slowed down and is mainly induced by materials such as calcium, silicon, and magnesium leached from NUKON™ and concrete. Furthermore, it is newly found that the spay buffer agent, tri-sodium phosphate, to form protective coating on the aluminum surface and reduce aluminum leaching is not effective for a large amount of aluminum and a long spray.