摘要:

A variational treatment of the burnup optimization of continuous scattered refueling is presented and numerical solutions are given for a slab reactor. It is made quantitatively clear how the reactor dimension, the xenon and the Doppler feedback reactivity, the burnup dependence of fission cross section and the reflector performance affect the power distribution that maximizes the average discharge exposure. Power flattening and burnup maximization are contradictory in general, but are consistent if, and only if, the condition of the perfect reflection at the core boundary is satisfied. The optimal power distribution is peaked in the central—and depleted in the outer region; and becomes flatter as the reflector performance is increased. The maximum average burnup depends on the burnup dependence of fission cross section and the strength of the Doppler and the xenon feedback reactivity, even if the average burnup calculated by the point-reactor model is the same. The former effect on the optimal power distribution is very small but the latter effects greatly contribute to power flattening. Both effects reduce the maximum burnup and the effects of the latter two are of comparable order. As the reactor becomes smaller, the maximum burnup decreases almost linearly to the neutron leakage. Optimal refueling has an advantage of more than 10% in the average burnup over the conventional flat-refueling rate method. However the difference from the flat-burnup method is very small, considering that the optimal refueling is handicapped by its very bad power distribution.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20357

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

A low-order discrete ordinates model for the solution of a certain class of three-dimensional neutron-transport problems is described. The method can be applied to cuboidal configurations with a region structure that allows the use of constant mesh spacings in each of the three coordinate directions. The angular flux distribution in a unit mesh cell is described in terms of discrete directions connecting the midpoints of 14 neighbor cells. A three-dimensional multigroup discrete ordinates code 3DT has been written forx, y, z-geometry which allows calculation of various configurations for small critical assemblies with computing speed far surpassing Monte Carlo techniques. The computed results for individual fuel-block reactivity worths of the fast thermionic critical experiment of Gulf General Atomic are in most cases in excellent agreement with experiment.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20358

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

Size-dependent extrapolation distances for pulsed-neutron experiments in light-water, spherical, non-multiplying systems have been determined by calculating the buckling in theB-1, 30-group approximation corresponding to a given decay constant. The decay constants for spheres of various radii were taken from an earlier work which reported 30-groupSncalculations of decay constants as a function of system radius.The same 30-group,B-1 method was also used to calculate pulsed-neutron-decay constants as a function of buckling over a wide range of buckling. The static or poisoning experiment inverse-relaxation length, as a function of concentration of a one-over-vpoison, was also computed in the same approximation. The resulting data were combined and fitted to yield values of the neutron-diffusion parameters

ISSN:0029-5639    

DOI:10.13182/NSE70-A20359

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

It is suggested that fast-neutron spectra can be represented by the expressionThe parameters of this representation can be determined from experimental results, such as activation integrals, or from calculated group fluxes, by the least-squares method. A practical procedure to derive the parameters from results of multigroup calculations is given, and possible applications of smoothing the stepping spectra are discussed.The method was successfully applied to various spherical metallic critical systems. Some examples are given, and the quality of the resulting spectra is discussed.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20360

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

The problem of precise calculation of spatial distributions of capture in resonance absorbers is crucial to the design of layered shields. Errors in spatial distribution of capture occur in multigroup neutron-transport calculations because of the necessarily broad energy groups employed. The single average-capture cross section in each group results in large underestimates of the capture rates near surfaces of resonance absorbers. Consequently, the spatial-capture gamma-ray generation and escape fraction are also in error.A method is presented for computing spatial-resonance-capture rates in thick layers. It employs group-effective resonance integrals to precalculate group-effective resonance cross sections that are universal functions of distance into the absorptive layer. The method is illustrated for captures in238U for the energy region 0.5 eV to 100 keV.The method is applied to a spherical reactor-shield configuration that contains alternate layers of depleted uranium and lithium hydride. Detailed comparison is made of the results of a discrete ordinates multigroup calculation with those of the present method. The comparison shows that the difference in spatial-capture distribution of theSnbroad treatment of resonance capture causes the capture gamma-ray dose to be always underestimated. For example, the difference in spatial-capture distribution in a 7-cm slab of238U causes the leakage dose to be a factor of 2 smaller than that obtained with the present method. The apparent generality of the present method suggests that it may be applied directly to the results of layered shield calculations made bySnbroad-group methods.Application of the method to the experimental variation of epicadmium capture with depth from the surface of metallic-uranium rods up to 5 cm in diameter as measured by Hellstrand provided spatial capture rates that agreed with experiment very well.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20361

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

Calculations of the differential photon-production cross sections from proton-nucleus collisions in the energy range 15 to 150 MeV have been carried out and compared with experimental measurements on12C,16O,27Al, and56Fe. The calculations are based on the intranuclear-cascade-evaporation model of nuclear reactions and simple assumptions about the deexcitation of excited nuclei. The calculated total photon-production cross sections are within roughly a factor of two of the experimental values, but the calculated photon spectra are not in good agreement with the experimental spectra.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20362

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

The ratio of the neutron capture to fission cross section (α) has been measured for239Pu in the energy range from 100 eV to 30 keV. Neutron time-of-flight techniques were used to obtain data with an energy resolution of approximately 10% at 10 keV. The data yield an averageα= 0.80±0.05 between 0.10 and 10 keV for an energy-independent incident neutron spectrum. Also,αdata were obtained in the resolved resonance region below 100 eV.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20363

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

Total neutron cross sections of bismuth were measured with resolutions of<3 keV over the energy range 0.2 to 1.4 MeV. Differential elastic-scattering cross sections were determined at intervals<50 keV from 0.3 to 1.5 MeV with resolutions of∼20 keV. The inelastic-neutron excitation of a state at 896±1 keV was observed and the respective differential excitation cross sections determined with incident resolutions of≥12 keV. Partially resolved resonance structure was evident in all the measured values. The experimental results were assayed for possible intermediate structure and were compared with the results of optical model and statistical calculations. The model calculations were inclusive of contributions due to the fluctuation and correlation of compound-nucleus resonance widths and of the shell closure atN= 126.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20364

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

The paper introduces the application of dynamic programming algorithms to the optimal allocation of energy in large nuclear-powered complexes. The formulation and solution of the problem of optimal product mixes in both purely industrial and agro-industrial complexes is discussed. Simplified numerical examples of each case are presented to illustrate the solution method.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20365

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

Steam-water, two-phase critical flows were obtained in long pipes (L/D>40) for mass flow rates ranging from 512 to 6460 lbm/(sec ft2), exit pressures from 40 to 150 psia, and thermodynamic equilibrium qualities from 0.0019 to 0.216. A comparison of the three test sections employed indicates that previous experimental data are in error for qualities less than 0.10 due to the influence of the downstream two-dimensional expansion on wall pressure taps located near the exit plane.Although simultaneous temperature and pressure measurements were not taken, the data exhibit trends that suggest the existence of a nonequlibrium phase change. Experimentally determined exit and axial void fractions indicate (a) that the velocity ratios are considerably less than the existing analytical predictions and (b) that previously dissolved gases existing from the liquid provide a source for vapor formation under adiabatic subcooled conditions.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20366

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor