Actinide breeding and reactivity variation in a thermal spectrum ADSR – Part 1: Development of a lumped thermal reactor model

The beneficial properties of fast reactor systems in being able to both burn and breed actinides have led to renewed interest in this technology as a means of providing a more sustainable form of nuclear power production. However, despite significant investment over many years in the development of the technology, fast reactors have never been deployed in significant numbers. In view of the difficulties encountered in fast reactor development, enhancements to the existing, well proven light water reactor (LWR) technology may provide a more accessible path to improved sustainability.     

Optimal parameter choice of CR–RC~m digital filter in nuclear pulse processing

CR–RC~m filters are widely used in nuclear energy spectrum measurement systems. The choice of parameters of a CR–RC~m digital filter directly affects its performance in terms of energy resolution and pulse count rate in digital nuclear spectrometer systems. A numerical recursive model of a CR differential circuit and RC integration circuit is derived, which shows that the shaping result of CR–RC~m is determined by the adjustment parameter(k, it determines the shaping time of the shaper)and the integral number(m). Furthermore, the amplitude–frequency response of CR–RC~m is analyzed, which shows that it is a bandpass filter; the larger the shaping parameters(k and m), the narrower is the frequency band. CR–RC~m digital Gaussian shaping is performed on the actual sampled nuclear pulse signal under different shaping parameters. The energy spectrum of ~(137)Cs is measured based on the LaBr_3(Ce) detector under different parameters. The results show that the larger the shaping parameters(m and k), the closer the shaping result is to Gaussian shape, the wider is the shaped pulse, the higher is the energy resolution, and the lower is the pulse count rate. For the same batch of pulse signals, the energy resolution is increased from 3.8 to 3.5%, and the full energy peak area is reduced from 7815 to 6503. Thus, the optimal shaping parameters are m=3 and k=0:95. These research results can provide a design reference for the development of digital nuclear spectrometer measurement systems.     

Solution of two-dimensional space–time multigroup reactor kinetics equations by generalized Padé and cut-product approximations

New methods based on the class of Padé and cut-product approximations are applied to the solution of the multigroup diffusion theory reactor kinetics equations in two space dimensions. The methods are shown to be consistent and numerically stable. The stability of the developed approximations is studied and it is in general A(α)-stable, where 0 ? α ? π/2 and therefore they are quite efficient in the presence of extreme stiffness, as shown by numerical results for some typical test cases. The system of stiff coupled differential equations is represented in a matrix form and due to the particular structure of this matrix, new algorithm based on the back-substitution is proposed for analytical inversion of the “A” matrix. The method has been tested for different benchmark problems. The results indicated that this method can allow much larger time steps and thus save much computational time as compared to the other conventional methods.     

An investigation of steam–water countercurrent flow model in TRACE

This paper studies the countercurrent flow model in the TRACE code version 5.0. Steam and water are chosen as the working fluids that flow counter-currently in a circular pipe. Three types of countercurrent flow models, including the Wallis, Kutateladze and Bankoff correlations, are investigated. A single tube model was built to study the Wallis and the Kutateladze correlations, and the variable in the calculation model is the pipe diameter. A perforated plate model was constructed to study the Bankoff correlation, and the variables include the pipe and hole diameters, the number of holes and the plate thickness. The hydraulic diameter of the pipe varied from 2.5 to 200 mm for the tests on the Wallis and Kutateladze correlations. To validate the Bankoff correlation, the hydraulic diameter of the pipe was varied from 50 to 200 mm, and the plate thickness varied from 10 to 40 mm. In this study we validate the countercurrent flow model in the TRACE code, and comment on the application ranges of the three correlations.     

Investigating the elliptic anisotropy of identified particles in p–Pb collisions with a multi-phase transport model

The elliptic azimuthal anisotropy coe cient (v₂) of the identified particles at midrapidity (■) was investigated in p–Pb collisions at■ Te V using a multi-phase transport model (AMPT).The calculations of di erential v₂ based on the advanced flow extraction method of light flavor hadrons (pions,kaons,protons,andΛ) in small collision systems were extended to a wider transverse momentum (p_T) range of up to 8 GeV/c for the first time.The string-melting version of the...     

Nuclear alternating parity bands and transition rates in a model of coherent quadrupole–octupole motion in neutron-rich barium isotopes

Deformed even–even nuclei Barium isotopes with quadrupole–octupole deformations are investigated on the basis of a collective model.The model describes energy levels of the yrast band with alternating parity in the neutron-rich~(140;142;144;146;148)Ba.The structure of the alternating parity bands is examined by odd–even (△I=1) staggering diagrams.An analytical method of the collective model is proposed for the calculation of E2 transition probabilities in alternating spectra of the nuclei~(140;142;144;146)Ba.     

Analytical developments in the Wong–Fung–Tam–Gao radiation model of thermal diffusivity

When the thermal diffusivity, χ, of a thin film on a substrate is measured by means of the mirage method, the photothermal deflection of the probe beam is determined by the heat radiation field contributed by the film and the substrate, heated by the pump beam. A two-dimensional algorithm is here presented in order to deduce the measure of the diffusivities of the film and the substrate in one set of mirage detection from the experimental data.     

A model of silver–iodine reactions in a light water reactor containment sump under severe accident conditions

Metallic silver and iodine form insoluble AgI in the containment sump which has a major impact on iodine volatility and hence on the source term to the environment. Resistance-in-series models are developed and validated against separate-effects tests. The reaction between I₂ and Ag is limited by mass transfer in the liquid. The rate does not follow a parabolic law for the duration of the experiments. The extent of oxidation of the silver sample seems to play a decisive role for reactions with I⁻ which proceed via a two-step process. The initial, rapid step is controlled by the reaction with the surface silver oxide with a contribution of mass transfer in the liquid. The subsequent, slow step is limited by reaction between I⁻ and Ag⁺ at the solid–liquid interface. The reaction is probably negligible for pH > 7 and in the absence of oxidising conditions.     

Determination of ^129I in IAEA-375 Reference Material

^79Se是一长寿命、纯β裂变产物核素，β能量为0．151MeV。^79Se半衰期已被测量过5次，每次测得数据间在误差范围内不吻合。随着新的测量手段的不断涌现，对^79Se半衰期重新进行测量很有必要。     

Experimental Investigation of Processes Occurring in the Plasma of a Cesium–Barium Tasitron

The results of measurements of plasma parameters in different regions of a nonstationary discharge in a cesium–barium tasitron with 1-sec time resolution are presented. Data analysis made it possible to determine the quenching mechanism of a discharge in a three-electrode system with large-structure grid. 7 figures, 12 references.     

Determination of ~(129)I in IAEA-375 Reference Material

129I is a long life radionuclide. During the analysis of 129I in soil samples, mixed-alkaline fusion and alkaline-peroxide fusion were used for sample digestion. The results show that the former method is simpler than the latter except for a little lower …     

Hybrid–PIC simulation of sputtering product distribution in a Hall thruster

Hall thrusters have been widely used in orbit correction and the station-keeping of geostationary satellites due to their high specific impulse,long life,and high reliability.During the operating life of a Hall thruster,high-energy ions will bombard the discharge channel and cause serious erosion.As time passes,this sputtering process will change the macroscopic surface morphology of the discharge channel,especially near the exit,thus affecting the performance of the thruster.Therefore,it is necessary to carry out research on the motion of the sputtering products and erosion process of the discharge wall.To better understand the moving characteristics of sputtering products,based on the hybrid particle-in-cell (PIC) numerical method,this paper simulates the different erosion states of the thruster discharge channel in different moments and analyzes the moving process of different particles,such as B atoms and B+ ions.In this paper,the main conclusion is that B atoms are mainly produced on both sides of the channel exit,and B+ ions are mainly produced in the middle of the channel exit.The ionization rate of B atoms is approximately 1％.     

Flow characteristics of natural circulation in a lead–bismuth eutectic loop

Lead and lead-alloys are proposed in future advanced nuclear system as coolant and spallation target.To test the natural circulation and gas-lift and obtain thermal-hydraulics data for computational fluid dynamics(CFD) and system code validation, a lead–bismuth eutectic rectangular loop, the KYLIN-Ⅱ Thermal Hydraulic natural circulation test loop, has been designed and constructed by the FDS team. In this paper, theoretical analysis on natural circulation thermal-hydraulic performance is described and the steady-state natural circulation experiment is performed. The results indicated that the natural circulation capability depends on the loop resistance and the temperature and center height differences between the hot and cold legs. The theoretical analysis results agree well with,while the CFD deviate from, the experimental results.     

Study of thorium–uranium based molten salt blanket in a fusion–fission hybrid reactor

Not only solid fuels, but also liquid fuels can be used for the fusion–fission symbiotic reactor blanket. The operational record of the molten salt reactor with F–Li–Be was very successful, so the F–Li–Be blanket was chosen for research. The molten salt has several features which are suited for the fusion–fission applications.The fuel material uranium and thorium were dissolved in the F–Li–Be molten salt. A combined program, COUPLE, was used for neutronics analysis of the molten salt blanket. Several cases have been calculated and compared. Not only the influence of the different fuels have been studied, but also the thickness of the molten salt, and the concentration of the ⁶Li in the molten salt.Preliminary studies indicate that when thorium–uranium–plutonium fuels were added into a F–Li–Be molten salt blanket and with a component of 71% LiF–2% BeF₂–13.5% ThF₄–8.5% UF₄–5% PuF₃, and also with the molten salt thickness of 40 cm and natural concentration of ⁶Li, the appropriate blanket energy multiplication factor and TBR can be obtained.The result shows that thorium–uranium molten salt can be used in the blanket of a fusion–fission symbiotic reactor. The research on the molten salt blanket must be valuable for the design of fusion–fission symbiotic reactor.     

Improvement of a physical model for blockage formation of solid–liquid mixture flow with freezing for core safety evaluation of SFRs

The SIMMER code has been developed to analyze event progression during core disruptive accidents (CDAs) in sodium-cooled fast reactors. One of the key phenomena during CDAs is the discharge of molten fuel from the core region which reduces the reactivity effectively. The discharge flow is inhibited by blockage formation due to freezing of the molten fuel. Then, the blockage formation is enhanced by unmolten fuel which forms solid–liquid mixture flow with the molten fuel. A physical model for blockage formation of solid–liquid mixture flow with freezing in the SIMMER code is improved in this study to dissolve some inconsistencies between the modeling and the physical phenomena involved in the solid–liquid mixture flow with freezing for more precise evaluation of CDA. The improved model is validated with a systematical procedure through a benchmark analysis of an experiment. Consequently, experimental penetration behaviors are simulated reasonably by the SIMMER code analysis with the improved model while excessive blockage formation occurred in the analysis with the original model.     

Cyclic softening as a parameter for prediction of remnant creep rupture life of a Indian reduced activation ferritic–martensitic (IN-RAFM) steel subjected to fatigue exposures

Sequential fatigue-creep tests were conducted on Indian reduced activation ferritic–martensitic steel at 823 K leading to sharp decrease in residual creep life with increase in prior fatigue exposures. Extensive recovery of martensitic-lath structure taking place during fatigue deformation, manifested as cyclic softening in the cyclic stress response, shortens the residual creep life. Based on the experimental results, cyclic softening occurring during fatigue stage can be correlated with residual creep life, evolving in an empirical model which predicts residual creep life as a function of cyclic softening. Predicted creep lives for specimens pre-cycled at various strain amplitudes are explained on the basis of mechanism of cyclic softening.     

Coupled model analysis of the ablative Rayleigh–Taylor instability

The weakly nonlinear stage of the ablative Rayleigh–Taylor instability(ARTI) is investigated by expanded hydrodynamic equations in which the third-order corrections of the two-mode perturbations are considered. In the present coupling model, two linear perturbations are simultaneously added near the ablation front at the initial moment, and we have derived the first three coupling harmonics. Furthermore, the coupling model analysis is studied via direct numerical simulation as well. When the ori...