Ratio Of Reaction Rate Research Articles

Cold nuclear fusion in metallic hydrogen and normal metals.

The rate of nuclear fusion from tunneling in very dense metallic hydrogen in the core of Jupiter is calculated to be 10{sup {minus}50} per hydrogen-deuterium pair per second. It is estimated that the width of the fusion barrier for deuterium in palladium or a similar metal must be reduced to, of order, 0.1 A for the fusion rate to be 10{sup {minus}25} per deuterium per second. If this scale is achieved, the ratios of various nuclear reaction rates will be very different for cold versus thermonuclear fusion.

Benchmark Physics Tests in the Metallic-Fueled Assembly ZPPR-15

Results of the first benchmark physics tests of a metallic-fueled, demonstration-size, liquid-metal reactor (LMR) are reported. A simple, two-zone, cylindrical conventional assembly was built with three distinctly different compositions to represent the stages of the Integral Fast Reactor fuel cycle. Experiments included criticality, control, power distribution, reaction rate ratios, reactivity coefficients, shielding, kinetics, and spectrum. Analysis was done with three-dimensional nodal diffusion calculations and ENDF/B-V.2 cross sections. Predictions of the ZPPR-15 reactor physics parameters agreed sufficiently well with the measured values to justify confidence in design analyses for metallic-fueled LMRs.

Measurements of reaction rates in zone-type cores of fast critical assembly simulating high conversion light water reactor.

Measurements of reaction rates have been performed in three uranium-fueled zone-type cores of the FCA constructed for a series of experiments on a high conversion light water reactor (HCLWR). These cores possess central test zones of different fuel enrichments and moderator to fuel volume ratios. Radial and axial fission rates of 236U, 239Pu, 238U and 23,Np were measured in each test zone by means of the micro-fission counter traverse. A region where the fundamental mode spectrum is established in the test zone were determined by utilizing these fission rate distributions. Central reaction rate ratios relative to the 235U fission rate were obtained from the measurements by the micro-fission counters and metallic uranium foils to examine changes in the reaction rate ratios among the three cores. The measured data were analyzed by the SRAC code system on the basis of the nuclear data file JENDL-2. The calculated fission rate distributions agree well with the experimental results for the all cases. The resul...

Experimental study of nuclear characteristics of large axially heterogeneous core using fast critical assembly.

The physics characteristics of large axially heterogeneous liquid-metal fast breeder reactors (LMFBRs), particularly the parameters for use in design and safety assessment, were examined using the JAERI fast critical assembly facility, arranged in Assembly XH-1, a partial mock-up of axially heterogeneous LMFBR. The properties measured were (1) criticality, (2) reaction rates and reaction rate ratios, (3) material sample worths, (4) sodium-void worths and (5) B4C control rod worths. The results were compared with those of prior experiments with assemblies representing conventional homogeneous core. Confirmation was obtained of the typical nuclear characteristics attributed to axially heterogeneous LMFBRs, including flattening of the axial distribution of power and of the differential worth of control rod, as also lower sodium void worth. Theoretical analyses paralleling the experiments, using JENDL-2 cross section library and JAERI standard calculation code system for fast reactor neutronics, resulted in s...

Analysis of irreversible complex chemical reactions and some observations on their overall activation energy

The nature of the overall reaction and its activation energy are investigated for both competitive and multiple reactions resulting from a one-step, irreversible, first-order reaction. For the competitive reaction model, the overall reaction is a function of the rates of the individual reactions in the reaction mixture. The rate constant of the competitive reaction in most cases can be represented satisfactorily by the Arrhenius equation. If the ratios of the individual reaction rates vary significantly with temperature, then the activation energy of the competitive reaction may vary with temperature and becomes a function of the activation energy of the most dominating reaction. The nature of the multiple reaction is a strong function of the individual reaction rates and the initial composition of the reaction mixture. It is demonstrated that a set of independent first-order reactions cannot be approximated by a single first-order multiple reaction having a lower activation energy than any of the reactions in the set. Possible reasons for previously reported “ low” activation energies observed in coal and biomass pyrolysis studies are briefly discussed.

Investigation of the Void Coefficient and Other Integral Parameters in the PROTEUS-LWHCR Phase II Program

Comparisons of calculated and measured neutron balance components are reported for the 7. 5% fissile plutonium reference test lattice of the PROTEUS-light water high conversion reactor (LWHCR) phase II program, both wet (with H//2O) and dry (100% void). Special experimental techniques have been developed and applied, particularly for k// infinity , and the range of directly measured reaction rate ratios has been extended. For the two cell codes tested, WIMS-D/1981 library and KARBUS/KEDAK-4, specific shortcomings have been identified; the new measurements have been found to be significantly more representative and accurate than the earlier phase I experiments.

Dependence on ethylene of the induction of phenylalanine ammonia-lyase activity in rice leaf infected with blast fungus.

The application of ethephon (ETP), an ethylene generating chemical, to press-injured rice leaves induced PAL (EC 4.3.1.6) activity. This induction disappeared when the concentration was low. A Scatchard plot for ligand binding gave a linear relationship between the PAL reaction rate at the time for the maximum rate of induction (tm) along the sigmoidal progress and the ratio of the PAL reaction rate versus ETP in a specific range of concentration. A similar application of glutamate (Glu) induced PAL activity, and the application of 1-aminocyclopropane-l-carboxylic acid (ACC) also induced PAL activity. The induction of rice leaf PAL with Glu was inhibited in the presence of tiron (TR), a superoxide scavenger, was weakly inhibited with aminooxyacetic acid (AOA), but was not inhibited with abscisic acid (ABA). The induction with ACC was also inhibited in the presence of TR, was weakly inhibited with AOA, and further was weakly inhibited with ABA. The inoculation of blast fungus conidia or application of fungal proteoglucomannan (RIF) to press-injured rice leaves induced PAL activity. The induction proceeded along sigmoidal curve accompanying the distinct auto-inactivation phase. Each approximated tm (midpoint of an individual sigmoidal curve) was determined; tm = 2.4hr with an incompatible race, tm = 5.3 hr with a compatible race, and tm= 11.0 hr with RIF stimulation. The 3 inhibition profiles of TR, AOA and ABA upon rice leaf PAL induction either with inoculation or with stimulation were quite similar to the inhibition profiles upon PAL induction with Glu.

Sensitivity Analysis of Cell Neutronic Parameters in High-Conversion Light-Water Reactors

The sensitivity coefficients of neutronic performance parameters in high-conversion LWR cells have been calculated by means of the SAINT code. In order to show the specific features of the sensitivity coefficients in the HCLWR cells, the differences between sensitivities were investigated for cells with different moderator to fuel volume ratios and different Pu enrichments. The burnup dependence of the sensitivities was also discussed with an emphasis on the effect of fission products on the cell parameters. We have performed the sensitivity analysis for the PROTEUS cores. Group constants of main heavy nuclides were compared for the different cell calculational methods; SRAC and VIM, and the different cross section libraries; JENDL-2 and ENDF/B-IV. The effect of the differences in group constants was estimated for the cell parameters k ∞, reaction rate ratio and coolant void worth. The differences in the 238U capture and 239Pu fission group constants in the resolved and unresolved resonance range produced 0.3∼1.0% change in k ∞ and 1∼6% change in the coolant void worth. These effect was largely dependent on the coolant void fraction.

Thermal conductivity of pressed lithium hydride and tritide compacts

In this work, the implementation of a collision history-based approach to sensitivity/perturbation calculations in the Monte Carlo code SERPENT is discussed. The proposed methods allow the calculation of the effects of nuclear data perturbation on several response functions: the effective multiplication factor, reaction rate ratios and bilinear ratios (e.g., effective kinetics parameters). SERPENT results are compared to ERANOS and TSUNAMI Generalized Perturbation Theory calculations for two fast metallic systems and for a PWR pin-cell benchmark. New methods for the calculation of sensitivities to angular scattering distributions are also presented, which adopts fully continuous (in energy and angle) Monte Carlo estimators.

Sensitivity analysis of cell neutronic parameters in high-conversion light-water reactors.

The sensitivity coefficients of neutronic performance parameters in high-conversion LWR cells have been calculated by means of the SAINT code. In order to show the specific features of the sensitivity coefficients in the HCLWR cells, the differences between sensitivities were investigated for cells with different moderator to fuel volume ratios and different Pu enrichments. The burnup dependence of the sensitivities was also discussed with an emphasis on the effect of fission products on the cell parameters. We have performed the sensitivity analysis for the PROTEUS cores. Group constants of main heavy nuclides were compared for the different cell calculational methods; SRAC and VIM, and the different cross section libraries; JENDL-2 and ENDF/B-IV. The effect of the differences in group constants was estimated for the cell parameters k ∞, reaction rate ratio and coolant void worth. The differences in the 238U capture and 239Pu fission group constants in the resolved and unresolved resonance range produced...

Effects of Fuel Enrichment on the Physics Characteristics of Plutonium-Fueled Light Water High Converter Reactors

Investigations have been carried out for three additional cores of the phase 1 experimental program on light water high converter reactor test lattices in the PROTEUS facility. An 8% (average) fissile plutonium tight-pitch lattice with a fuel/moderator volumetric ratio of 2.0 was considered. As for the earlier reported 6% (average) fissile plutonium test lattice, H/sub 2/O, Dowtherm, and air were the moderator state investigated. Significant enrichment-dependent trends have been identified in the comparisons of calculated and experimental results for the wet (moderated cases, particularly for the important reaction rate ratio of /sup 238/U capture of /sup 239/Pu fission. These are then reflected in the comparison of moderator voidage characteristics, expressed in terms of individual components of the kinfinity void coefficient.

On the box model for prediction of water quality in eutrophic lakes

Using the box model, a method of prediction of water quality in eutrophic lakes is discussed. As to the box segmentation of the lake concerned, three subjects are emphasized: box number, locations of partition, and accuracy or error of the model. The box model is one of approximations deduced from the advection-dispersion differential equations, and comparing the moment of concentration pattern between model and theory, the reasonable box model is proposed for shallow and eutrophic lakes, of which the physical parameters, Peclet number and the biochemical parameter, and the ratio of reaction rate and advection ratio are given. This model applied to Lake Kasumigaura, a typical eutrophic lake in Japan, has good coincidence with the result of field survey, and applicability for other shallow lakes was also confirmed.

On the measurement of integral data in thermally driven LWHCR lattices

Abstract Integral reaction rate ratios and other k∞ -related measurements were carried out in Light Water High Converter Reactor (LWHCR) test lattices with different moderator states. The reaction rates were measured using fission chambers, foil activation or solid state track recorders. The main problems were associated with foil effects in the rodded, wet lattices. The estimated uncertainties on the various measured and evaluated integral data are discussed.

Tritium production and foil reaction rates in a large lithium sphere by D-T neutrons

Abstract The benchmark data on tritium production-rate in a 120cm diameter lithium sphere are compared with one dimensional calculations by the Monte Carlo transport code MCNP using the nuclear data files of ENDF/B-IV and JENDL-3PR1, as the reaction-rate ratio data to the 93Nb(n,2n) reaction. Overestimation of the 7Li(n, n'α)t cross section values in the ENDF/B-IV file has been clearly concluded.

Effects of recent wims data library changes on calculational results for LWHCR lattices

A set of adjustments to the data library used in conjunction with the U.S. wims code was recently reported by Halsall. The relatively large effects of the recommended data changes on the prediction of LWHCR neutron-balance components are discussed in the context of lattice measurements carried out at the PROTEUS reactor facility. The consistency of both k ∞ and reaction rate ratio results has been found to improve markedly with the new data library. An apparent shortcoming which remains, however, is the overprediction of reactivity for a fully-voided LWHCR core.

Mechanism of the photochemical reduction of CCl bond in fluorine compounds

The photochemically initiated substitution of a halogen for hydrogen atom represents a preparative reaction, that can be expressed by the general scheme: ▪ The reaction is characterized by a high selectivity in polyhalogeno compounds as demonstrate examples of successfully performed preparations: CF 3CBr 2Cl → CF 3CHBrCl, CCl 2FCClF 2 → CHClFCClF 2, CF 3CClFCCl 3 → CF 3CClFCHCl 2. A marked directive effect on the regioselectivity of the reduction is exhibited by the ester group in fluorinated propanoates: CFXYCClZCOOR → CFXYCHZCOOR (X,Y = F,Cl). The quantum yields of this reduction in 2-propanol are as high as several hundreds of units, which is indicative of the chain mechanism. The photo-reduction is auto-sensitized by the resulting acetone. The kinetic model of the reduction indicates, under a definite ratio of the terminal reaction rates, a rate limit independent of the concentration of the starting substance. The kinetic model of the reduction initiated by α-phenyl benzoin and benzoin isopropyl ether was verified also using the Stern-Volmer dependence of a total quantum yield of HCl.

Optimization by lumped control of reactors with langmuir‐hinshelwood catalyst deactivation

AbstractA method is proposed for solving the problem of temperature optimal control in tubular fixed‐bed reactors with reaction systems described by Langmuir‐Hinshelwood‐Hougen‐Watson kinetic equations. The optimization problem is formulated by N state differential equations corresponding to the N differential fixed‐bed reactors in which the integral reactor is divided. It is solved using the control vector parameterization computational technique. The proposed method when applied to a simple reaction system reported previously in the literature gives analogous results, and thus validates the theory. This theory is applied to the dehydrogenation of benzyl alcohol to benzaldehyde. An analysis of optimality problem shows a strong influence of the temperature dependence of the ratio of reaction rate to deactivation reaction rate on the optimal policy.

Comparison of cell models for analysis of heterogeneous fast critical assembly.

We have investigated cell calculation models to be used in the analysis of neutronic characteristics of a heterogeneous fast critical assembly. As cell models we have considered a single drawer model with a critical buckling, a single drawer model with group dependent bucklings and a multidrawer model which consists of some fuel and blanket drawers. We have compared the cell averaged cross sections obtained from these cell models with the results of a reference transport calculation and estimated the effects of the cell models on k eff, reaction rate ratios, reaction rate distributions and sodium void worths in the heterogeneous fast critical assembly ZPPR-13A. The multidrawer model and the single drawer model with group dependent buckling give reasonable cell averaged cross sections and have large effects on k eff and 238U fission rate distribution.

Reactivity and Reaction Rate Ratio Changes with Moderator Voidage in a Light Water High Converter Reactor Lattice

Integral reaction rate ratios and other k∞-related parameters have been measured in the first three cores of the experimental program on light water high converter reactor (LWHCR) test lattices in the PROTEUS reactor. The reference tight-pitch lattice consisted of two rod types, with an average fissile-plutonium enrichment of 6% and a fuel/moderator ratio of 2.0. The moderators were H2O, Dowtherm (simulating an H2O voidage of 42.5%), and air (100% void). Comparisons of the measured parameters have been made with calculational results based mainly on the use of two separate codes and their associated data libraries, namely, WIMS-D and EPRI-CPM.A reconstruction of individual components of the k∞ void coefficient has been carried out on the basis of the measured changes with voidage of the various reaction rate ratios, as well as of k∞ itself. The subsequent more detailed comparisons between experiment and calculation should provide a useful basis for resolving the conflicting calculational results that have been reported in the past for the void coefficient characteristics of LWHCRs.

Kinetic Study of Proton Tunneling in the Reaction between 2,4,6-Trinitrotoluene and 1,8-Diazabicyclo[5.4.0]undec-7-ene in Benzonitrile

Abstract The proton tunneling has been examined for the reaction between 2,4,6-trinitrotoluene and 1,8-diazabicyclo[5.4.0]undec-7-ene in benzonitrile in view of the solvent effect on the rate ratio kH⁄kD as well as on the various activation parameters. The reaction rate ratio kH⁄kD diminishes from 18.3 at 15 °C to 14.5 at 35 °C. The difference in the activation energies EaD–EaH is 8.8 kJ mol−1 and the ratio of Arrhenius preexponential factors is 2.5. All these values are greater than the semiclassical limits of the primary kinetic isotope effects. According to Bell’s equation the remarkable isotope effect is due to considerable contribution from tunneling in benzonitrile. The present results, being compared with those in other aprotic solvents, are discussed in relation with the effects of solvent polarity, specific acid–solvent interaction, and geometrical bulkiness in the vicinity of the reaction site.