摘要:

AbstractAn approximate form of the transport equation is used to investigate stationary and time-dependent neutron slowing down and propagation in the field of gravity. The approximation is based on the expansion of theδfunction of the transfer function in a power series of a small parameter s, the ratio of the neutron to atom masses.It is shown that the s and s2approximations in the stationary neutron slowing down problems are connected with Wigner and Grueling-Goertzel approximations. A simple formula is given for time-dependent neutron slowing down.The influence of the field of gravity on the operation of a reactor and on the propagation of ultra cold neutrons is studied in the point-energy approximation. Also investigated is the neutron space-energy distribution in the field of gravity.

ISSN:0029-5639    

DOI:10.13182/NSE80-A21302

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractEnergy spectra of delayed neutrons from the precursors93,94,95Rb and143Cs have been measured by use of an on-line mass spectrometer and a3He neutron spectrometer. Details of the experimental techniques, data analysis, and error estimates are given. A comparison of delayed-neutron spectra for87Br,93,94,95Rb, and143Cs measured by three different laboratories is presented. Peak structures are reproduced by all laboratories, but the relative intensities below 200 keV vary according to different measurement or data analysis techniques.

ISSN:0029-5639    

DOI:10.13182/NSE80-A21303

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractDifferential cross sections for neutron-induced gamma-ray production from sodium have been measured for incident-neutron energies between 0.2 and 20.0 MeV. Gamma rays with energies 0.35≤Eγ≤10.6 MeV were detected with a sodium iodide spectrometer at 125 deg. The data presented are the double-differential cross section, d2σ/dΩdE, for coarse intervals in incident-neutron energy. The measured results are compared with existing data, with calculations based on multistep Hauser-Feshbach theory, and with a benchmark gamma-ray production measurement performed at the Oak Ridge Tower Shielding Facility (TSF). Average agreement between our measured results and model calculations is within 15%. The cross sections measured at the TSF are typically 30% larger than our results, except for gamma-ray energies between 1.1 and 1.5 MeV where the TSF benchmark predicts a yield 20 times greater than we observe. Results of the present measurement have been incorporated for the gamma-ray production in the Evaluated Nuclear Data File.

ISSN:0029-5639    

DOI:10.13182/NSE80-A21304

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractThe importance of gamma-ray reactions [(γ,f), (γ,γ′), and (γ,n)] that can interfere with the detection of certain threshold neutron reactions [(n,f), (n,n′), and (n,2n)] used in reactor pressure vessel dosimetry was studied via a combined experimental and calculational program. First, an experiment-design calculation of such photocontamination was carried out in a pool-type reactor, indicating∼0.1% photointerference at the reactor surface and∼10 000% at 1-m penetration of water (∼1% neutron attenuation/mm). Next, a complete set of threshold activation foils was irradiated fore and aft of a“photofraction gauge,”a tungsten disk that attenuated the important 5- to 10-MeV gamma rays by a factor of∼30 and the>0.5-MeV neutrons by a factor of∼3. The photofraction gauge was calibrated for photofraction fγ, by comparing the large fore to aft activation ratios [R(F/A)] for photocontamination foils with R(F/A)≃3 for noncontamination foils [such as58Ni(n,p) and27Al(n,α)]. The values of fγwere calculated and were found to agree reasonably well with those measured, except that the calculated values were a bit too high. The one-dimensional calculation needs to be replaced with an accurate three-dimensional calculation with measured power distribution before accurate (γ,f) and (γ,γ′) cross-section adjustments can be made for the activation foils and/or the gamma-ray production cross sections (from n,γreactions near the reactor) properly modified.Some one-dimensional cylindrical calculations for pressurized and boiling water reactors are presented that predict up to 55% photocontamination at the pressure vessel wall when determined by the232Th(n,f) reaction.

ISSN:0029-5639    

DOI:10.13182/NSE80-A21305

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractThe behavior of contained aerosols following a hypothetical accident of a liquid-metal fast breeder reactor is analyzed. The effects of turbulent coagulation, thermophoretic deposition, and reduced agglomerate density are included in the analysis. The method of moments is utilized as a solution procedure and is discussed in some detail. Calculated results are compared with previous laboratory measurements. The predictions of the suspended aerosol concentration are found to be somewhat conservative but in general agreement with experimental results.

ISSN:0029-5639    

DOI:10.13182/NSE80-A21306

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractIn the anisotropic source flux iteration technique for solving the radiation transport problems for evaluating the flux integral, the source within the mesh was approximated to a linear form using the nodal source values. It is shown in this Note that at the start of each iteration, in addition to the nodal sources, the source integral over the mesh is also available. Using the source integral as an additional parameter, several linear approximations and a quadratic approximation for the source distribution within the mesh are possible. This Note discusses the relative merits of the various approximations. A comparative analysis of these approximations with the different difference schemes currently in use is also given. Among the linear schemes, the ones retaining the source integral and the gradient or source integral and the terminal nodal source provide very good accuracy. It is also shown that the quadratic scheme retaining both the nodal sources and the source integral provide far more accurate results without significant increase in computer time or memory.

ISSN:0029-5639    

DOI:10.13182/NSE80-A21307

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractThe neutron slowing down process is frequently studied by means of a pulsed-electron beam from a Linac impinging on a heavy metal target. The resulting pulses of photoneutrons are thermalized and the differential spectrum is measuredviathe time-of-flight method. If the thermalizing medium contains deuterium or beryllium, a secondary distributed photoneutron source is produced by the gamma-ray flash from the Linac. The magnitude of this secondary source in D2O was measured by foil activation and it was shown that the effect of the secondary source can be accurately evaluated.

ISSN:0029-5639    

DOI:10.13182/NSE80-A21308

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractStatic calculations using the computer code LEOPARD have been used to investigate the effect of fuel rod motion on neutron-density noise during core burnup of a pressurized water reactor (PWR). These calculations show a variation with burnup in agreement with the experiment and give approximate quantitative agreement with the experiment for the root-mean-square value of the noise for reasonable assumed values of fuel rod motion. It is suggested, therefore, that fuel rod motion is a likely source of neutron-density noise in a PWR.

ISSN:0029-5639    

DOI:10.13182/NSE80-A21309

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractReliable and safe operation of a nuclear power plant or any other complex network of flow-connected subunits requires prompt detection and location of failed subunits. An algorithm is described, which performs (in many cases) unambiguous automatic location of single or multiple failures. Types of failures that cannot be located unambiguously are characterized. The algorithm can be applied to networks with a serial array of subunits, with converging or branching nodes or with feedback. An optimal structure of the algorithm is identified that allows the maximal failure locating capability with a minimum of logical or arithmetical manipulation. This is important especially for application to large systems. The dynamic behavior of the algorithm is examined for a simple system.

ISSN:0029-5639    

DOI:10.13182/NSE80-A21310

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE80-A21311

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor