摘要:

AbstractAn alternate pump trip criterion is described that meets the intent of the U.S. Nuclear Regulatory Commission pump trip requirement [i.e., to minimize primary system mass loss during a small-break loss-of-coolant accident (SBLOCA)] while providing the operators with a valuable tool to differentiate between various generic types of off-nominal transient conditions (heatup, cooldown, and loss-of-coolant accident) and to determine the efficacy of the recovery from these transients. The technique also provides a reliable measure of primary system mass inventory during heatup and cooldown transients and in the early phases of an SBLOCA. This method was developed by examining pump response to a variety of transients conducted in the Loss-of-Flow Test (LOFT) Facility. To explain the data, a mathematical model was developed based on one-dimensional pump theory. The response of the LOFT pumps was extended to full-scale commercial pressurized water reactor (PWR) pump response by examining general centrifugal pump behavior and by calculating PWR response to an SBLOCA. The results of the study indicate that the PWR pump behavior can be expected to be similar to that measured in LOFT and that the pump model can be used to gain valuable information on the status of a PWR during off-nominal transient conditions.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23858

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe fission cross sections of247Cm,254Es, and250Cf are measured with the Rensselaer intense neutron spectrometer from 0.1 eV to 80 keV. The cross sections are normalized to the235U ENDF/B-V broadened cross section. Fission areas and resonance widths are determined for low-energy resonances in247Cm. The254Es and250Cf fission cross sections are the only reported measurements for these isotopes. The254Es isotope is the heaviest odd-odd isotope ever measured over this energy range. The thermal fission cross sections for247Cm,254Es, and250Cf are determined by extrapolation of the low-energy region of the cross section and are in good agreement with other reported measurements. Resonance integrals are reported for the energy range of 0.1 eV to 80 keV, and the areas for247Cm and250Cf resonances are also reported. The previously reported246Cm fission cross section was corrected for fission in247Cm.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23859

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractCumulative238U(p, f) cross sections are given for 37 nuclides in the energy region 12.5 to 17.5 MeV and for four nuclides up to 30 MeV. Also, 11 independent cross sections are reported. A theoretical model for calculating such quantities is described. The calculated cumulative cross sections are in relatively good agreement with the experimental values, except in the region of symmetric fission, where the calculated values are smaller. The measured total fission cross sections are in good agreement with previous results. From the independent cross sections, the influence of the nuclear shell Z = 50 on the charge distribution of fission fragments can be seen clearly.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23860

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractProposals are made for improving the homogeneous diffusion procedure for reactor operating and design calculations. The procedure is based on the use of homogeneous properties for the assemblies and on high-order discretization for the reactor diffusion calculations. It proposes to improve the radial leakage model incorporated in the flux calculation and to introduce a super-homogénéisation equivalence technique between the flux and cross-section edit calculations to yield homogeneous diffusion properties consistent with the control rod worth calculations.

ISSN:0029-5639    

DOI:10.13182/NSE109-360

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA seminumerical technique developed for solving the transport equation in slab geometry is adopted for a point isotropic source of gamma rays in spherical geometry. Only Compton scattering is dealt with currently. Two quantities, namely surface flux and surface source, are introduced to circumvent singularities at the origin. A collision-by-collision iterative approach is followed to solve the coupled form of integral transport equations separating the spatial and energy transmission kernels. The spatial transmission kernel for obtaining surface flux from surface source is derived. The energy angle transmission kernels are evaluated by taking recourse to Legendre polynomial expansions. The uncollided and first collision surface fluxes are obtained analytically. An appropriate functional form is chosen for the spatial interpolation of flux and source facilitating large spatial mesh widths.The computer program ASFIT-Sphere is written on the basis of these formulations. Energy flux spectra and angular distributions obtained by the current method of scattered photons 2 and 3 mean-free-paths away from a137Cs source in water are compared with the data of ANS-6 shielding benchmark experiments. Comparison with calculations by other methods is also included.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23862

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractSpectral measurements of intermediate-energy neutrons (i.e., En≤65 MeV) transmitted through iron, lead, graphite, and concrete shields are described. Concurrently, transmitted spectra of associated gamma rays are also obtained.A collimated beam of neutrons induced by 65-MeV protons in a thick copper target is utilized in the measurements. Measurements of both neutrons and gamma rays penetrating the shields are by an NE-213 scintillator.Monte Carlo calculations using the MORSE code are carried out with the DLC-87 Hilo multigroup cross sections.For neutron spectra, comparison between the measured and calculated spectra indicates that the DLC-87 data reproduce the measured data well for the graphite and the concrete shields but give only slightly higher values at energies of 15 to 30 MeV for the iron shield and overpredict the lead-transmitted spectra.Tests on the cross sections reveal that the underestimation of the total iron cross section by the DLC-87 in the 15- to 25-MeV energy range is the reason for the overestimation of the iron transmitted spectra. Neglecting the elastic scattering in evaluating the lead data is the reason for the large overestimation of the lead transmitted spectra.Gamma-ray spectra obtained behind the graphite and concrete shields are well explained by the transmission of source gamma rays from the copper target through the shields. However, the intensity of the measured photons behind iron and lead shields is much larger than that of transmitted source photons. The discrepancies are not explained by including neutron-induced gamma rays for neutrons from thermal energy up to 15 MeV. The gamma-ray production cross-section data may be required for neutrons>15 MeV to explain the remaining large discrepancies.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23863

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractCalculational studies are conducted of neutron and gamma-ray transport in the beam tubes of a proposed high-flux reactor for the Advanced Neutron Source. To avoid excessively long computing times, the calculations were carried out by coupling two, two-dimensional discrete ordinates calculations. The calculational methodology used is briefly described.Calculated results are presented of the thermal neutron, nonthermal neutron, and gamma-ray fluxes in a radial and a tangential beam tube. Both scalar and angular fluxes in and at the exit of the beam tubes are given. When compared with the radial beam tube, the tangential beam tube shows a lower flux of high-energy neutrons and a much lower flux of gamma rays. The spectral characteristics of the particle fluxes at the exits of the beam tubes are similar to those at the entrances.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23864

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA previously reported analytical model describing gas motion in nuclear-reactor-pumped lasers is extended to incorporate spatially nonuniform initial gas density fields. This model is solved analytically, and the solution is used to study the damping of density perturbations in the gas induced by fission-fragment heating. An approximate scaling relation is found that describes the reduction in the root-mean-square density perturbation in terms of the heating-induced pressure rise normalized by the initial pressure. This damping process is shown to be relatively independent of the spatial frequency of the initial density perturbation field.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23865

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe concept of microfission, whereby a small target of fissile material is burned under compression, was introduced nearly 20 years ago; the size of the target is limited by the magnitude of the compression and by the initial number of fissions that start the chain reaction. A burst of antiprotons at maximum compression can allow target size to be significantly reduced. Antiprotons were previously shown to be a strong source of neutrons and pions; under conditions of high density, they enable a significant reduction in burn time and, hence, target size. Possible applications are discussed, including space propulsion and intense neutron and X-ray sources.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23866

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractSome approximate estimators for obtaining the fluence at a point in Monte Carlo neutron transport calculations are presented and compared with the commonly used next event estimator. These estimators do not require direct evaluation of the scattering probability using Legendre expansions of the differential angular cross sections. The estimators are particularly useful for Monte Carlo programs that sample scattering directions in the center-of-mass coordinate system.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23867

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor