Tight Lattices Research Articles

Synchrotron infrared nanospectroscopy in fourth-generation storage rings.

Fourth-generation synchrotron storage rings represent a significant milestone in synchrotron technology, offering outstandingly bright and tightly focused X-ray beams for a wide range of scientific applications. However, due to their inherently tight magnetic lattices, these storage rings have posed critical challenges for accessing lower-energy radiation, such as infrared (IR) and THz. Here the first-ever IR beamline to be installed and to operate at a fourth-generation synchrotron storage ring is introduced. This work encompasses several notable advancements, including a thorough examination of the new IR source at Sirius, a detailed description of the radiation extraction scheme, and the successful validation of our optical concept through both measurements and simulations. This optimal optical setup has enabled us to achieve an exceptionally wide frequency range for our nanospectroscopy experiments. Through the utilization of synchrotron IR nanospectroscopy on biological and hard matter samples, the practicality and effectiveness of this beamline has been successfully demonstrated. The advantages of fourth-generation synchrotron IR sources, which can now operate with unparalleled stability as a result of the stringent requirements for producing low-emittance X-rays, are emphasized.

Calculation methodology of fast fission factor in a thermal reactor

This article describes the coefficient of the fast fission, which is part of the formula of «four factors». Considered, to exist at the moment, two methods for calculation of the coefficient of the fast fission in uranium-water tight lattices. Also presents the results of calculations and comparative analysis of the data obtained by two techniques.

Local thermal–hydraulic behaviour in tight 7-rod bundles

Advanced water-cooled reactor concepts with tight lattices have been proposed worldwide to improve the fuel utilization and the economic competitiveness. In the present work, experimental investigations were performed on thermal–hydraulic behaviour in tight hexagonal 7-rod bundles under both single-phase and two-phase conditions. Freon-12 was used as working fluid due to its convenient operating parameters. Tests were carried out under both single-phase and two-phase flow conditions. Rod surface temperatures are measured at a fixed axial elevation and in various circumferential positions. Test data with different radial power distributions are analyzed. Measured surface temperatures of unheated rods are used for the assessment of and comparison with numerical codes. In addition, numerical simulation using sub-channel analysis code MATRA and the computational fluid dynamics (CFD) code ANSYS-10 is carried out to understand the experimental data and to assess the validity of these codes in the prediction of flow and heat transfer behaviour in tight rod bundle geometries. Numerical results are compared with experimental data. A good agreement between the measured temperatures on the unheated rod surface and the CFD calculation is obtained. Both sub-channel analysis and CFD calculation indicates that the turbulent mixing in the tight rod bundle is significantly stronger than that computed with a well established correlation.

CFD analysis of thermal–hydraulic behavior in SCWR typical flow channels

Investigations on thermal–hydraulic behavior in SCWR fuel assembly have obtained a significant attention in the international SCWR community. However, there is still a lack of understanding and ability to predict the heat transfer behavior of supercritical water. In this paper, CFD analysis is carried out to study the flow and heat transfer behavior of supercritical water in sub-channels of both square and triangular rod bundles. Effect of various parameters, e.g. thermal boundary conditions and pitch-to-diameter ratio on the thermal–hydraulic behavior is investigated. Two boundary conditions, i.e., constant heat flux at the outer surface of cladding and constant heat density in the fuel pin are applied. The results show that the structure of the secondary flow mainly depends on the rod bundle configuration as well as the pitch-to-diameter ratio, whereas, the amplitude of the secondary flow is affected by the thermal boundary conditions, as well. The secondary flow is much stronger in a square lattice than that in a triangular lattice. The turbulence behavior is similar in both square and triangular lattices. The dependence of the amplitude of the turbulent velocity fluctuation across the gap on Reynolds number becomes prominent in both lattices as the pitch-to-diameter ratio increases. The effect of thermal boundary conditions on turbulent velocity fluctuation is negligibly small. For both lattices with small pitch-to-diameter ratios ( P/ D < 1.3), the mixing coefficient is about 0.022. Both secondary flow and turbulent mixing show unusual behavior in the vicinity of the pseudo-critical point. Further investigation is needed. A strong circumferential non-uniformity of wall temperature and heat transfer is observed in tight lattices at constant heat flux boundary conditions, especially in square lattices. In the case with constant heat density of fuel pin, the circumferential conductive heat transfer significantly reduces the non-uniformity of circumferential distribution of wall temperature and heat transfer, which is favorable for the design of SCWR fuel assemblies.

A Qualitative Reactivity and Isotopic Assessment of Fuels for Lead-Alloy-Cooled Fast Reactors

Various methods have been proposed to transmute and thus consume the current inventory of transuranic waste from spent light water reactor (LWR) fuel and plutonium from weapons. We discuss the neutronics performance of nonfertile, fertile metallic, and fertile nitride fuels loaded with 20 to 30 wt% LWR-grade plutonium plus minor actinides and burned in an open-lattice lead-alloy–cooled fast reactor, with an emphasis on the fuel cycle life and spent fuel isotopic content. As a comparison, similar fuel was also studied in a sodium-cooled fast reactor. Our calculations show that the average actinide burn rate for fertile-free fuel is similar for both the sodium- and lead-bismuth–cooled cases, ranging from 1.02 to 1.16 g/MWd, compared to a typical LWR actinide generation rate of 0.303 g/MWd. In addition, our calculations show that the effective full-power days (EFPDs) of operation (or equivalent reactivity-limited burnup) using fertile fuel can extend beyond 20 yr, and the average actinide burn rate is similar for both the sodium- and lead-bismuth–cooled cases, ranging from 0.5 to 0.9 g/MWd. Using the same parameters (i.e., a large pitch-to-diameter ratio, same linear power, and fissile/fertile loading, etc.), the lead-alloy-cooled cases had an EFPD that was 18% to several times greater than their sodium-cooled counterparts. However, tight sodium-cooled lattices are equivalent to the looser lead-alloy lattices in terms of beginning-of-life excess reactivity.

Analysis of Seven NEPTUN-III (Tight-Lattice) Bottom-Flooding Experiments with RELAP5/MOD3.3/BETA

Seven tight-lattice NEPTUN-III bottom-flooding experiments are analyzed by using the frozen version of RELAP5, RELAP5/MOD3.3/BETA. This work is part of the Paul Scherrer Institute (PSI) contribution to the High Performance Light Water Reactor (HPLWR) European Union project and aims at assessing the capabilities of the code to model the reflooding phenomena in a tight hexagonal lattice (which was one of the core geometries considered at the time for an HPLWR) following a hypothetical loss-of-coolant accident scenario. Even though the latest version of the code has as a default the new PSI reflood model developed by the author, which was tested and assessed against reflooding data obtained at standard light water reactor lattices, this work shows that for tight lattices, the code underpredicts the peak clad temperatures measured during a series of reflooding experiments performed at the NEPTUN-III tight-lattice heater rod bundle facility. The reasons for these differences are discussed, and the (possible) changes needed in the framework of RELAP5/MOD3.3 for improving the modeling of reflooding in tight lattices are investigated.

Modified Conversion Ratio Measurement in Light Water-Moderated UO2Lattices

To investigate the accuracy of the neutronic calculations in various neutron spectra, the modified conversion ratios [(MCR): ratio of {sup 238}U capture rate-to-total fission rate] of four kinds of light water-moderated UO{sub 2} fuel lattices were measured. In the measurements, the relative reaction rates of {sup 238}U capture and total fission were obtained from the nondestructive gamma-ray spectrometry of {sup 239}Np and {sup 143}Ce, respectively, which accumulated in the fuel rod irradiated at the Tank-Type Critical Assembly. The moderator-to-fuel volume ratios V{sub m}/V{sub f} of the measured lattices were 1.50 (undermoderate) to 3.00 (overmoderate). The measured MCRs were 0.477 {+-} 0.014(V{sub m}/V{sub f} = 1.50), 0.434 {+-} 0.013(1.83), 0.383 {+-} 0.011(2.48), and 0.356 {+-} 0.011(3.00), respectively. The Monte Carlo calculation employing the JENDL-3 library showed good agreement with the experiments for all the cores, although they showed a tendency of overestimation for larger values of MCR, as shown in the case of UO{sub 2} tight lattices. Therefore, it was concluded that, for the cores investigated, the accuracy of the neutronic calculation method currently used was very good.

Measurements and Analyses of the Ratio of238U Captures to235U Fission in Low-Enriched UO2Tight Lattices

The ratio of 238U captures to 235U fissions (C8/F5) was measured for four kinds of light- water moderated UO2 lattice cores; 1.42S, 1.00S, 0.75S and 0.56S. These cores have a central tight lattice test region surrounded by a normal lattice driver region. In the test region, the volume ratios of water-moderator to fuel are 1.420, 1.000, 0.750 and 0.564, respectively. Measurements were carried out using uranium metal foils set in a fuel rod at the center of the test region. The radial distributions of relative C8 and F5 rates in the fuel rod were also measured for the 1.42S and 0.56S cores. Calculations were performed by using the continuous energy Monte Carlo code MVP with the JENDL-3 library. The calculated C8/F5's were larger than the experimental ones, and the discrepancy between the calculated in-fuel C8 distribution and the experimental one was observed. From the results of the sensitivity analysis, it is found that the decrease of the resonance 238U capture cross section and the increase of the resonance 235U fission cross-section reduced the discrepancy between the calculation and the experiment in the C8/F5 ratios and their in-fuel distributions, respectively.

Reflooding of Tight Lattice Bundles

Results regarding analytical bottom reflooding experiments in a 37- and a 127-heater rod bundle are presented for two different tight lattices. A comparison between these two geometries and with the standard pressurized water reactor (PWR) array shows a degradation of cooling efficiency when the cross section of the subchannels is decreased. The core heat sinks (guide thimbles and water tubes'') are seen to have a noticeable influence on the overall cooling of the bundle, and it is confirmed that a combined top/bottom injection does not significantly improve cooling efficiency. Calculations with CATHARE 1.3 code adjusted for the standard PWR array are presented (zero heat sinks), but results have to be confirmed over a wider range of parameters.

Measurements and Analyses of the Ratio of 238U Captures to 235U Fission in Low Enriched UO2 Tight Lattices.

The ratio of 238U captures to 235U fissions (C8/F5) was measured for four kinds of light- water moderated UO2 lattice cores; 1.42S, 1.00S, 0.75S and 0.56S. These cores have a central tight lattice test region surrounded by a normal lattice driver region. In the test region, the volume ratios of water-moderator to fuel are 1.420, 1.000, 0.750 and 0.564, respectively. Measurements were carried out using uranium metal foils set in a fuel rod at the center of the test region. The radial distributions of relative C8 and F5 rates in the fuel rod were also measured for the 1.42S and 0.56S cores. Calculations were performed by using the continuous energy Monte Carlo code MVP with the JENDL-3 library. The calculated C8/F5's were larger than the experimental ones, and the discrepancy between the calculated in-fuel C8 distribution and the experimental one was observed. From the results of the sensitivity analysis, it is found that the decrease of the resonance 238U capture cross section and the increase of the resonance 235U fission cross-section reduced the discrepancy between the calculation and the experiment in the C8/F5 ratios and their in-fuel distributions, respectively.

Fundamental aspects of brittle cooperative phenomena — local load sharing models

The present paper considers the effect of stress concentrations on the damage evolution in brittle solids with disordered microstructure. This problem is herein approached studying discrete models provided with a local load sharing rule. Two of these models: tight bundle parallel bar model and lattices, are employed to establish universal trends in brittle cooperative deformation processes.

Prediction of natural mixing in tightly packed seven-rod bundles ( [formula omitted

In this study the predicted fine structure of flow within a seven-rod bundle at a fixed rod-to-rod gap distance ( P/D = 1.1) and at different rod-bundle-to-wall distances are presented ( N Re = 10 5 ; N Pr ≈ 1.0 ). The numerical code VANTACY-II has been used to calculate the single-phase, fully developed turbulent flow conditions in arbitrary two-dimensional solution domains. The code includes a validated model of the anisotropic turbulent exchange of momentum and heat appropriate for tight lattices. The different rod-bundle boundary structures affect the fluid flow conditions, although the influence of the hydraulics on the temperature field is partly compensated by the turbulent microconvective heat transport between the central and the wall subchannels. In other words, the turbulent mixing depends to a great extent on the size and on the wetted perimeter of the edge region. It may be concluded that a distributed parameter approach using two-dimensional turbulence models is • bb modelling the flow in detail, providing the local distributions of the fluid velocities and temperatures, the wall shear stresses and the wall heat fluxes, and integral quantities like the axial pressure gradient • bb helping to interpret experiments and to expand their results • bb and providing well defined input data for lumped-parameter analysis codes.

Accuracy of Cell Calculation Methods Used for Analysis of High Conversion Light Water Reactor Lattice

Validation tests were made for the accuracy of cell calculation methods used in analyses of tight lattices of a mixed-oxide (MOX) fuel core in a high conversion light water reactor (HCLWR). A series of cell calculations was carried out for the lattices referred from an international HCLWR benchmark comparison, with emphasis placed on the resonance calculation methods; the NR, IR approximations, the collision probability method with ultra-fine energy group. Verification was also performed for the geometrical modelling; a hexagonal/cylindrical cell, and the boundary condition; mirror/white reflection. In the calculations, important reactor physics parameters, such as the neutron multiplication factor, the conversion ratio and the void coefficient, were evaluated using the above methods for various HCLWR lattices with different moderator to fuel volume ratios, fuel materials and fissile plutonium enrichments. The calculated results were compared with each other, and the accuracy and applicability of each met...

Reactor Physics Calculations for Alternative Fuel Recycling Strategies Using Tight Pressurized Water Reactor Lattices

Physics calculations have been performed for repeated plutonium recycling in tight pressurized water reactor lattices. These calculations made use of the transport theory code CASMO combined with a 70-group nuclear data library variant that was created recently. The calculational model, which performs well for normal thermal reactors, was tested against measured data for tight lattices from the Swiss reactor PROTEUS. The test results are reasonably good and the model was applied to tight lattice power reactors without any modification. Four reactor systems, three of which contain tight lattices with plutonium recycling, were treated. The fourth one represents recycling in a normal lattice. Calculated results are given for various parameters. Particularly important are the natural uranium savings in the tight lattice systems relative to net consumption in the normal lattice system. The values found are between 10 and 35% for an --50-yr operating time for each system. However, in some of the calculations, the void reactivity results are positive. For these cases, there may actually be positive values in reality - especially in the latter part of the time period studied - which would lead to restrictions and somewhat reduced savings.

The French Thermal-Hydraulic Program Addressing the Requirements of Future Pressurized Water Reactors

In the framework of feasibility studies of future pressurized water reactors, a thermal-hydraulic program has been established in order to qualify computer codes in three fields: critical heat flux and reflooding heat transfer in triangular rod bundle arrays with tight lattices and the coolability of movable fertile rods in their guide tubes. Tests carried out at the Commissariat a l'Energie Atomique in cooperation with Electricite de France and Framatome are now in progress, and preliminary results are shown for these three studies.

Critical Heat Flux Correlation for Triangular Arrays of Rod Bundles with Tight Lattices, Including the Spiral Spacer Effect

Etablissement d'une nouvelle correlation pour le flux thermique critique dans des faisceaux de barres a reseau serre. Comparaison avec des donnees experimentales obtenues avec des faisceaux de tube avec espaceurs a fils helicoidaux

Continuum tight binding models and quantum transport in the presence of dynamical disorder

Continuum limits of various tight binding linear chain lattices used in the author's recent study of quantum transport in the presence of dynamical disorder, are analyzed from the point of view of their energy level spectra when disorder is absent. These spectra show a linear dispersion similar to that in the Luttinger model, and describe the energy levels of the corresponding discrete systems in the range of midband wavevectors. Next, the more conventional longwavelength continuum limit, which describes the energy levels of the actual discrete systems near the bottom of the bands is discussed. On the basis of these properties it is argued that the applicability of the continuum models to the study of dynamical properties is restricted to low frequencies in the range of low lying excitations, near the midband Fermi level in half-filled band situations in the case of the midband models, and near the bottom of a nearly empty band for the longwavelength models. Finally, it is shown that in the presence of dynamic disorder the longwavelength continuum limit of a single-band tight-binding model leads to nondiffusive motion, with a mean squared displacement ∼t3, fort→∞.

Uranium in Volcanic Rocks: Progress: ABSTRACT

Calc-alkaline rocks of crustal(?) derivation analyzed 0 to 5 ppm uranium in magmatic phases, but hundreds of ppm in epigenetic end-products. Alkaline rocks of mantle(?) derivation analyzed 0 to 22 ppm in magmatic phases, 30 to 45 ppm in deuterically modified phases and hundreds of ppm in final epigenetic modifications. Incompatibility with rock-forming silicates relegates large ions including uranium to residual gas or fluid. Mantle volatiles released during magma generation or crystallization mineralize rocks according to relative chemical reactivity. In rocks with 60 ppm U show inclusions variably containing Th, REE, U, Ti, V, Ni, Cr, Cu, Pb, Zn, Ba, and Mn. Halogens, S, and P underscore the volatile role. Inclusion-laden asphaltite is common. Lattice inclusions may represent vapor trapped during crystallization. Those in cleavages, amygdules, or fractures appear epigenetic. Those lacking Th probably are of rel tively low temperature. Surface tension would inhibit liquid entry into tight textures and lattices, so volatile transport and ionic lattice diffusion are inferred. Inclusions account for most Th-U distribution patterns suggesting dominant epigenetic enrichment of volcanics by residual volatiles. End_of_Article - Last_Page 760------------

The void coefficient ‘Paradox’ for tight water lattices

The void coefficients in tight water lattices with enriched plutonium fuel were calculated. It was found that for the same fuel, the void coefficient is negative when the moderator is light water and positive when the moderator is heavy water. The explanation to this presumed anomally is given.

Experimental Analysis of Energy Spectrum Parameters in Slightly Enriched UO2-H2O Lattices

The relative neutron temperature represented by the activation ratio (AR) of Lu-Cu, and the modified epithermal index in the form were measured by foil activation for a wide range of water-to-fuel volume ratios, in slightly enriched UO2-H2O lattices. With tight lattices, the values of the activation ratio thus experimentally determined agree better with the two dimensional collision probability calculation than with the one dimensional cylindricalized cell calculation. The values of measured with the use of Au-Mn-Ni alloy foil without Cdfilter are in good agreement with the results calculated by the extended TEMPEST code. The neutron temperature Tn and the epithermal index r in a unit cell, derived from the quantities AR and , can be expressed respectively by from which, it is found that a linear relationship between is obtained in the form