Neutron spectra emitted in the fission of U235 at 0, 45, and 90 ° to the direction of motion of the fragments

Neutron spectra emitted at 0, 45, and 90 ° to the direction of motion of the fragments in the fission of U²³⁵ by 14.3 Mev neutrons have been measured. The angular distribution of the fission neutrons was found to be N(0 °): N(45 °): N(90 °) = (3.23 ± 0.12): (1.75 ± 0.07): 1.00. The experimental data are compared with spectra calculated on the assumption of an isotropic Maxwellianneutron distribution in the center-of-mass system of the fragment.     

Unsteady Reynolds Averaged Navier–Stokes simulation of the turbulent flow pulsation and coherent structures in a tight lattice in rolling motion

The flow in a tight lattice is strongly affected by the quasi-periodic lateral flow pulsations caused by large scale vortices. This kind of large scale vortices is largely responsible for the momentum and heat exchange across the gaps. In rolling motion, the coherent structure and flow oscillation are affected by an additional force. The coherent structure in rolling motion is more significant than that in no rolling motion. The oscillation period in rolling motion is about 10% bigger than that in no rolling motion. The rolling motion can affect the coherent structure. However, the effect of rolling motion on the thermal hydraulic parameters, i.e. wall temperature and bulk temperature, is very limited. The wall temperature and wall shear stress in rolling motion and no rolling motion are nearly the same. The additional force due to rolling motion can change the moving characteristics of coherent structures, but its effect on the turbulent flow and heat transfer is weak.     

Identification tables for use in the analysis of α and β activities

In order to facilitate the identification of activities being subjected to analysis, tables are compiled according to data published prior to 1958 containing the distribution of all known - and -radioactive isotopes as a function of their T_1/2, end-point energies of their -spectra, and -particle energies. The tables make it possible to establish a group of isotopes with a previously established T_1/2 and energies of radioactive emission. In a number of cases, the use of a scheme involving the radioactive decay chain may also prove expedient in the identification of activities.We consider it our duty to express our gratitude to Yu. A. Zysin for a discussion and his advice.     

Elastic–plastic analysis of the steel-to-tungsten transition joint for a high performance divertor

The use of tungsten as a plasma-facing material necessitates a transition joint to the oxide dispersion strengthened (ODS) steel or ferritic steel (FS) structural material of the primary coolant loop at the end of the divertor target plate where the surface heat flux is very low. A critical issue in the transition joints is the coefficient of thermal expansion (CTE) mismatch between the tungsten (or tungsten-alloy) and ODS steel, which can lead to unacceptably high thermal stresses during steady state and ratcheting during cyclic loads. Detailed 2D and 3D thermo-mechanical analyses were conducted to study the behavior of a transition from tungsten to FS with an intermediate layer of tantalum, located outside of the high heat flux region. The results include plastic strains under various loading conditions including fabrication processes, warm and cold shutdown, and allow for plastic behaviors leading to stress relaxation. The accumulation of plastic deformation may cause ratcheting. Modifications were proposed to the transition joint design in order to eliminate stress concentration and ratcheting under cyclic loading. The results of the modified design exhibited less plastic deformation in the joints as well as no ratcheting caused by warm and cold shutdown.     

An applied limit of the bunching method for the Feynman-α analysis

Feynman-α method is used as the representative method in reactor noise analysis for the criticality monitoring. Feynman-α analysis needs a large amount of measurement time in its original process, though many researchers use the bunching method and its derived methods for the experimental data processing to shorten the measurement time. However, the detailed characteristics and the application limit of the bunching method have not been researched and discussed enough. This paper shows a possibility that the Bunching method is a method to reduce the probability fluctuation with the Y value only in the appearance. Moreover, the criteria for determining that the Y value is not an accidental product are also provided in this paper.     

Non-dimensional analysis of static bifurcation in a natural circulation loop

The steady-state characteristics of a two-phase natural circulation loop were investigated based on the homogenous model. Transcendental equations of non-dimensional loop mass flow rate under various conditions were also derived. The static bifurcation diagram of a two-phase natural circulation described with non-dimensional variables Npch-m^＋ was obtained. In addition, various steady-state characteristics of a natural circulation loop were analyzed and discussed. These characteristics include the existence of multiple solutions under certain conditions, and the maximum mass flow rate. The authors also examined the effects of important parameters such as sub-cooling number, riser-to-heated-region length ratio, and riser-to-heated-region diameter ratio.     

A preliminary design and structural analysis of the lifting tools for 40° sector sub-assembly and handling ITER components

The purpose-built, ITER tokamak assembly tools, which are to be provided by Korea, should be designed to meet: the assembly plan, space reservations, safety standards, simple operations, efficient maintenance, and so on. It is very important that the ITER assembly tools are able to lift and transfer ITER components or their sub-assemblies to their assembled position safely. Furthermore, the lifting tools will lift and handle very heavy loads that can be more than 1200 tonnes sometimes. Therefore, the ITER lifting tools must be designed to endure these heavy load conditions with regard to their structural integrity. Also, these designs should be verified through an appropriate method. The preliminary design of the sector lifting tool and associated lifting attachments are introduced in this paper. The sector lifting tool was designed especially to lift and handle various ITER components by adjusting the lifting centre. The structural analysis results using ANSYS are described considering the heaviest load condition. The results of the analysis show that; all stresses applied on the lifting tool are lower than the allowable stress of the applied material.     

Predicting local distributions of erosion–corrosion wear sites for the piping in the nuclear power plant using CFD models

The erosion–corrosion (E/C) wear is an essential degradation mechanism for the piping in the nuclear power plant, which results in the oxide mass loss from the inside of piping, the wall thinning, and even the pipe break. The pipe break induced by the E/C wear may cause costly plant repairs and personal injures. The measurement of pipe wall thickness is a useful tool for the power plant to prevent this incident. In this paper, CFD models are proposed to predict the local distributions of E/C wear sites, which include both the two-phase hydrodynamic model and the E/C models. The impacts of centrifugal and gravitational forces on the liquid droplet behaviors within the piping can be reasonably captured by the two-phase model. Coupled with these calculated flow characteristics, the E/C models can predicted the wear site distributions that show satisfactory agreement with the plant measurements. Therefore, the models proposed herein can assist in the pipe wall monitoring program for the nuclear power plant by way of concentrating the measuring point on the possible sites of severe E/C wear for the piping and reducing the measurement labor works.     

CFD studies on the separation performance of a new combined gas–solid separator used in TMSR-SF

In order to comply with discharge standards, a gas–solid separator is used to remove solid particles from the thorium molten salt reactor-solid fuel(TMSR-SF)system. As a key component, it directly determines system energy efficiency. However, current gas–solid separators,based on activated carbon adsorption technology, result in high pressure drops and increased maintenance costs. In the present study, a new combined gas–solid separator was developed for the TMSR-SF. Based on a simplified computational fluid dynamics(CFD) model, the gas–solid twophase flow and the motion trajectory of solid particles were simulated for this new separator using commercial ANSYS 16.0 software. The flow and separation mechanism for this structure were also been discussed in terms of their velocity effects and pressure field distributions, and then the structure was optimized based on the influence of key structural parameters on pressure and separation efficiency. The results showed that the standard k–e model could be achieved and accurately simulated the new combined separator. In this new combined gas–solid separator, coarse particles are separated in the first stage using rotating centrifugal motion, and then fine particles are filtered in the second stage, giving a separation efficiency of up to 96.11%. The optimum blade inclination angle and numbers were calculated to be 45° and four, respectively. It implicated that the combined separator could be of great significance in a wide variety of applications.     

Assembly?oriented reliability analysis method for the top?connection structure of a nuclear fuel assembly

The nuclear fuel assembly is the core component of a nuclear reactor. In a pressurized water reactor fuel assembly, the topconnection structure connects the top nozzle to the guide thimble. Its performance reliability is essential for the stability of the nuclear fuel assembly. In this study, an assembly-oriented reliability analysis method for top-connection structures is presented by establishing an assembly-oriented top-connection structure parameter modeling method and a nonlinear contact ga...     

Calculation of the spectra of fission neutrons emitted at angles of 0, 45, and 90° to the direction of flight of the fragments

The evaporation model is used to solve the problem of the spectrum of neutrons emitted by fission Fragments at angIes of 0, 45, and 90° to the direction of flight of the fragments. It is assumed that the neutrons are emitted isotropically in a coordinate system associated with the fragment. The spectra calculated are in good agreement with the experimental data.Translated from Atomnaya Énergiya, Vol. 13, No. 6, pp. 530–533, December, 1962     

Proton induced γ-ray emission yields for the analysis of light elements in aerosol samples in an external beam set-up

The PIXE technique is a reliable tool for the characterisation of thin aerosol samples, but it can underestimate the lightest measurable elements, like Na, Mg, Al, Si and P, owing to the absorption of their X-rays inside the sample. The PIGE technique is a valid help to determine corrections for such effect: in order to perform PIGE measurements relative to thin reference standards in an external beam set-up, we measured, at the external beam facility of the Tandetron accelerator of the LABEC laboratory in Florence, the γ-ray yields as a function of the proton beam energy for the reactions ¹⁹F(p,p′γ)¹⁹F (E_γ = 110 and 197 keV), ²³Na(p,p′γ)²³Na (E_γ = 440 keV) and ²⁷Al(p,p′γ)²⁷Al (E_γ = 843 and 1013 keV), in the proton energy range from 3 to 5 MeV. The measured yields are shown, and the determined most suitable energies for performing PIGE quantification of Na and Al are reported, together with the corresponding minimum detection limits (MDLs). The results of some test on PIGE accuracy and an evaluation of self-absorption effects in PIXE measurements on thin aerosol samples are also presented.     

Silver surface enrichment of silver–copper alloys: a limitation for the analysis of ancient silver coins by surface techniques

The surface enrichment of archaeological silver–copper alloys has been recognized for many years. However, the origin of this enrichment is not well defined and many hypotheses have been put forward to account for this behaviour: segregation of the components during casting, deliberate thermal and/or chemical post-treatment, abrasion or corrosion. Among the hypotheses mentioned above, we have focused our study on the first step of coin manufacturing. Replications of silver–copper standards of various compositions ranging from 30% to 80% Ag, reflecting the composition of silver blanks, have been produced. Metallographic examination, PIXE and SEM–EDS have been used for the characterization of each sample. A model of the direct enrichment has been established. This model allows us to propose a relationship between the surface composition and the silver content of the core. Comparison with data of Roman coins from the Roman site of Châteaubleau (France) and from the literature and consequences for the analyses of ancient coins by surface methods are presented.     

Fabrication of a full-size mock-up for inboard 10° section of ITER vacuum vessel thermal shield

A full-scale mock-up of VVTS inboard section was made in order to validate its manufacturing processes before manufacturing the vacuum vessel thermal shield (VVTS) for ITER tokamak. VVTS inboard 10° section consists of 20 mm shells on which cooling tubes are welded and flange joints that connect adjacent thermal shield sectors. The whole VVTS inboard is divided into two by bisectional flange joint located at the center. All the manufacturing processes except silver coating were tested and verified in the fabrication of mock-up. For the forming and the welding, pre-qualification tests were conducted to find proper process conditions. Shell thickness change was measured after bending, forming and buffing processes. Shell distortion was adjusted after the welding. Welding was validated by non-destructive examination. Bisectional flange joint was successfully assembled by inserting pins and tightening with bolt/nut. Bolt hole margin of 2 mm for sector flange was revealed to be sufficient by successful sector assembly of upper and lower parts of mock-up. Handling jig was found to be essential because the inboard section was flexible. Dimensional inspection of the fabricated mock-up was performed with a 3D laser scanner.     

Three-dimensional FE analysis of the thermal–mechanical behaviors in the nuclear fuel rods

In order to implement numerical simulation of the thermal–mechanical behaviors in the nuclear fuel rods, a three-dimensional finite element model is established. The thermal–mechanical behaviors at the initial stage of burnup in both the pellet and the cladding are obtained. Comparison of the obtained numerical results with those from experiments validates the developed finite element model. The effects of the constraint conditions, several operation and structural parameters on the thermal–mechanical performances of the fuel rod are investigated. The research results indicate that: (1) with increasing the heat generation rates from 0.15 to 0.6 W/mm³, the maximum temperature within the pellet increases by 99.3% and the maximum radial displacement at the outer surface of the pellet increases by 94.3%. And the maximum Mises stresses in the cladding all increase; while the maximum values of the first principal stresses within the pellet decrease as a whole; (2) with increasing the heat transfer coefficients between the cladding and the coolant, the internal temperatures reduce and the temperature gradient remains similar; when the heat transfer coefficient is lower than a critical value, the temperature change is sensitive to the heat transfer coefficient. The maximum temperature increases only 7.13% when h changes from 0.5 W/mm² K to 0.01 W/mm² K, while increases up to 54.7% when h decreases from 0.01 W/mm² K to 0.005 W/mm² K; (3) the initial gap sizes between the pellet and the cladding significantly affect the thermal–mechanical behaviors in the fuel rod; when the gap size varies from 0.03 mm to 0.1 mm, the highest temperature in the pellet increases by 19.7%, and the maximum first principal stress at the outer pellet surface decreases by 17.4%; it is critical to optimize the gap size in order to reduce the pellet–cladding mechanical interaction and avoid their contact at early stage. This study lays a foundation for the further research on the irradiation-induced mechanical behaviors in the fuel rods.     

Study the Output Characteristics of a 90 kJ Filippove-Type Plasma Focus

The output characteristics of a Filippove-Type plasma focus “Dena” (288 μF, 25 kV, 90 kJ) is numerically investigated by considering the voltage, current, current derivative, and maximum current as a function of capacitor bank energy in the constant Argon gas pressure and compared to the experiment. It is shown that increase on the bank energy leads to the increment on the maximum current and decrement on the pinch time.     

Gamow-Teller Resonance of ~(90)Zr in a Relativistic Approach

We establish the formalism of nuclear spin-isospin excitations, especially the Gamow-Teller (GT)resonance in a fully consistent relativistic random phase approximation. A relativistic form of theLandau-Migdal parameter g'=0.6 is adopted as a residual spin-isospin correlation force. In thenon-relativistic limit it reproduces the excitation energy of the giant Gamow-Teller resonance state     

Development of a thermal–hydraulic analysis code for research reactors with plate fuels

The thermal–hydraulic analysis code THAC-PRR has been developed with Visual Fortran 6.5 for the investigation of plate type fuel reactors. It is based on the fundamental conservation of mass, momentum and energy, and proper constitutive correlations for flow friction factor, heat transfer and thermophysical properties. Moreover, a simple and improved lumped-differential method has been adopted to analyze the conjugate heat transfer between the fuel plate and the coolant. The Reactivity Insertion Accident (RIA) and Loss Of Flow Accident (LOFA), which have been defined in the IAEA 10 MW MTR Benchmark program, were analyzed with this developed program for the code-to-code validation. Good agreement was achieved. Furthermore, the accidents due to the partial (95%) and total (100%) blockage of one channel in the IAEA 10 MW MTR were investigated with THAC-PRR. The results showed that if the blockage occurred in the average channel, there was no boiling occurred even the channel was totally obstructed. The reason was that the heat was transferred to the adjacent channels by conduction through the fuel plates which formed the obstructed channel. However, if the blockage occurred in the hot channel, boiling did occur. This indicated that it is very important to consider the interaction between the blocked channel and the adjacent channels in this type of transient.