摘要:

AbstractA method for solving various infinite medium and half-space multigroup transport problems with anisotropic transfer is presented. A set of eigensolutions for the homogeneous multigroup equations is obtained and is shown to have“full-range”completeness and orthogonality properties. These properties then can be used to solve for the infinite medium Green's function. Half-space problems are solved in two distinct steps. First, the emergent distribution is calculated. Then, application of the full-range completeness property gives the complete solution everywhere in the half-space. The success of this method implies that the eigensolutions also possess a“half-range”completeness property.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19512

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractBy means of approximate numerical solutions obtained from a first-order correction to the prompt-jump approximation, good agreement is found with exact numerical solutions of the kinetics equations. Accuracies of<0.1% are obtainable for iterative time steps of as much as 1 sec, provided the reactor remains below prompt-critical [i.e.,k(t)<$1]. The accuracy increases asl/β→0, i.e., as the prompt-neutron lifetime becomes smaller or as the reactor becomes“faster.”This is true for both fast- and slow-reactivity insertion rates,C. Two methods for handling rapid reactivity insertion rates are discussed. One (Method A) is more applicable forC≈1→50 $/sec, and the other (Method B, which effectively shifts the time scale) is more applicable forC≳50 $/sec. In the one delayed-neutron-group approximation, analytic results are presented for arbitrary reactivity insertion rates and comparisons are made with previous methods.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19513

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractNeutron density and importance distributions,βeff/Λand moderator temperature coefficients have been experimentally studied in connection with a central water gap of a light-water reactor having a water to UO2volume ratio of 1.5. Thermal importance functions are determined from the reactivity weighting function, while the fast importance functions are measured by a252Cf source introduction method. Values ofβeff/Λmeasured by pulsed-neutron experiments decrease from 202 sec−1in the uniform core to 185 sec−1-for the core with a water gap of 6.7 cm effective radius. It is also shown that the water gap influences the moderator temperature coefficient to a considerable extent.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19514

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractThree methods are presented for calculating the multiplication of the delayed-neutron response which occurs in far-subcritical samples of fissionable material irradiated by an external neutron source: a three-energy group analytic expression; the zero prompt-lifetime approximation in conjunction with a one-dimensional steady-state transport theory code; and a three-dimensional time-dependent Monte Carlo code. The accuracy and limitations of the calculational techniques are demonstrated by a comparison with experimental measurements.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19515

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractThe neutron transport equation is solved in plane geometry for a moderator with a periodic temperature distribution using the synthetic scattering kernel of Williams. A simple correspondence between the new model and the heavy-gas model is found for physical quantities dependent on the first two eigenvalues of the kernel. A recursion procedure for solving the energy moments of the flux is also presented. The flux is determined by a method using singular eigenfunctions. Some numerical results for the mean energy of the flux as a function of the lattice length are presented for A = 8 or for A = 10 employing the heavy-gas model. In order to consider the effect of the periodicity of the temperature distribution on the mean energy of the neutron spectrum obtained, the results are compared to the mean energy of the neutron spectrum in Kottwitz geometry. There is a considerable deviation for lattices with lengths of the order of the rethermalization length. In this respect, the lattices with lengths of the order of ten rethermalization lengths describe Kottwitz geometry fairly well.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19516

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractElectron-photon cascade calculations have been carried out for zero-width beams of 1-GeV electrons normally incident on semi-infinite slabs of water and aluminum. The energy deposited as a function of depth and radius is presented and compared with experimental measurements. The overall agreement between the calculated and experimental results is quite good and is adequate for most shielding purposes.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19517

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA method of performing probability calculations for nuclear-reactor surface temperatures has been devised. The method gives consideration to the fact that some uncertainties may vary systematically over all the reactor or over some parts of it. The method does not depend on assumption of any particular form of the probability distributions. The method was used to do an example calculation for an MTR-type test reactor with plate-type fuel elements. It was shown that the calculated probability of failure, that is, that surface temperature exceeds coolant saturation temperature, lies closer to values obtained from the Deterministic Method than to values from the Statistical Method. The calculated probability value was identified as the probability of success at the instant of reactor startup. It was observed that the probability of success for continued operation might not be the same as the value for startup. The method gives an improved representation of the probability problem for reactor surface temperatures. However, there is still much to be learned about the various important distribution functions. In the present situation of inadequate knowledge of behavior and distributions of uncertainty factors, all such probability calculations must be regarded as providing only a rough approximation to the true probability of success for a reactor.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19518

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractTwo cylindrical specimens of UO2were irradiated in the Oak Ridge Research Reactor at temperatures up to 1700°C. Both specimens were of natural enrichment uranium (0.7%235U) but one specimen was a single crystal and the other had a fine-grain microstructure. The fission-gas release from these specimens were affected by the fission density, temperature, burnup, grain growth, and the cracking of the specimens. Concentrations of fission gas produced high local stresses which contributed to the cracking of the specimens. Spherical specimens of enriched (48.7%235U), fused, polycrystalline UO2were irradiated to study the effect of burnup and high fission density. The spherical specimens began breaking at 1.9% uranium burnup and continued to break into smaller fragments as the burnup continued to 4.6% uranium burnup. The primary cause of breaking was fission-gas pressure within the spheres rather than thermal stresses. Equiaxed grain growth in UO2occurs at∼1650°C and fission gas, normally trapped in a grain boundary, can then migrate along the mobile grain boundary. The fission-gas release rate is thus greatly increased during the time of grain growth but the increase in grain size has little influence on the subsequent gas release at lower temperatures. By the defect-trap model, the effect of an increase in fission density is to create more traps within the fuel and at the same time to generate more fission gas. Thus, although the concentration of fission gas within the specimen is proportional to the fission density (at equilibrium conditions) the escape rate of the fission gas is not proportional to the concentration, unless the fission density is very low. When the fission density is very high, however, the fission tracks will intersect and the fission gas may escape as if through interconnected diffusion pipes. The fission-gas release was found to increase exponentially with fission density above 1014fissions/(cm3sec).

ISSN:0029-5639    

DOI:10.13182/NSE69-A19519

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractMolten sodium (623 to 69°K) was injected by a pneumatic, piston spray-injector into a closed reaction chamber containing dry air or dry air-nitrogen mixtures. The rate of the pressure rise resulting from the sodium-air burning reaction was measured during the spraying interval. The pressure-rise rate was a measure of the reaction rate. The spray particle size had the most pronounced effect on the reaction rate, which increased as the particle size decreased. Increasing the spray velocity resulted in a modest increase in the reaction rate. The reaction rate decreased slowly as the oxygen content of the atmosphere was lowered until, at an oxygen concentration of 4 mol%, there was no visible burning.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19520

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA mathematical model was developed to predict the burning rate and burning temperature of a single spherical sodium particle moving through air or air depleted in oxygen. The model is based on the assumption that the reaction rate is controlled by the diffusion of oxygen to a combustion zone surrounding the particle. A quasi-steady state approach and an averaging technique were used to correlate the reaction rates of individual spray particles with the theoretical burning rate of a spray and the theoretical pressure rise in an enclosing volume. The theory correctly predicted the direction and magnitude of experimentally observed variations in reaction rate with respect to oxygen content, spray velocity, and particle size. The spray particle size was found to be the most important parameter when considering the sprayed sodium-air reaction.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19521

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor