摘要:

AbstractThe heat capacity Cpof UO2was measured in a laboratory experiment where sintered 0.5-to 1-mm-diam microspheres were heated by four tetrahedrally oriented laser beams in an inert-gas-filled autoclave at pressures up to∼1000 bar. The sample, suspended by a tungsten needle, was heated to 8000 K during pulses of a few milliseconds duration. The experimental technique, the instrumentation, and the analytical method used to deduce Cpfrom the experimental pulse-heating curves are described. Between the melting point Tmand∼4000 K, the heat capacity decreases to a value close to that given by the Neumann-Kopp rule for a triatomic, harmonic lattice, i.e., 9R. Near 5000 K, however, the heat capacity again increases, and it appears to saturate at a value∼30% higher by 8000 K. The new results are compared with published Cpvalues for molten UO2(and other relevant materials) and are briefly discussed in light of the established temperature dependence of Cpat T

ISSN:0029-5639    

DOI:10.13182/NSE93-A23990

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThe calculation of the space and energy dependence of the heavy nucleus resonant absorption in a heterogeneous lattice is one of the hardest tasks in reactor physics. Because of the computer time and memory needed, it is impossible to represent finely the cross-section behavior in the resonance energy range for everyday computations. Consequently, reactor physicists use a simplified formalism, the self-shielding formalism. As no clean and detailed experimental results are available to validate the self-shielding calculations, Monte Carlo computations are used as a reference. These results, which were obtained with the TRIPOLI continuous-energy Monte Carlo code, constitute a set of numerical benchmarks that can be used to evaluate the accuracy of the techniques or formalisms that are included in any reactor physics codes. Examples of such evaluations, for the new assembly code APOLLO2 and the slowing-down code SECOL, are given for cases of238U and232Th fuel elements.

ISSN:0029-5639    

DOI:10.13182/NSE93-A23991

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThe application of the Langevin equation method to the study of fluctuations in the space- and velocity-dependent neutron density as well as in the detector outputs in nuclear reactors is presented. In this case, the Langevin equation is the stochastic linear neutron transport equation with a space- and velocity-dependent random neutron source, often referred to as the noise equivalent source (NES). The power spectral densities (PSDs) of the NESs in the transport equation, as well as in the accompanying detection rate equations, are obtained, and the cross- and auto-power spectral densities of the outputs of pairs of detectors are explicitly calculated. The transport-level expression for the R(ω) ratio measured in the252Cf source-driven noise analysis method is also derived. Finally, the implementation of the Langevin equation approach at different levels of approximation is discussed, and the stochastic one-speed transport and one-group P1equations are derived by first integrating the stochastic transport equation over speed and then eliminating the angular dependence by a spherical harmonics expansion. By taking the large transport rate limit in the P1description, the stochastic diffusion equation is obtained as well as the PSD of the NES in it. This procedure also leads directly to the stochastic Fick’s law.

ISSN:0029-5639    

DOI:10.13182/NSE93-A23992

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThe development of a parallel stochastic cellular automata model for neutron transport is presented. The model is derived from neutron physics and is implemented on a 2048 processor singleinstruction multiple-data architecture MasPar computer. Purely absorbing and purely fissioning onedimensional benchmarks are performed against analytical solutions. Favorable results from these two benchmarks motivated the performance of three other test cases. Results for a two-dimensional scattering-absorbing case and a one-dimensional time-dependent case compared fairly well qualitatively with literature results. Also, results from a one-dimensional, two-group case compared somewhat favorably, but the scheme used was deemed not efficient enough without modification.

ISSN:0029-5639    

DOI:10.13182/NSE93-A23993

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractIn pressurized water reactors, the fuel reloading problem has significant meaning in terms of both safety and economics. The local power peaking factor must be kept lower than a predetermined value during a cycle, and the effective multiplication factor must be maximized to extract the maximum energy. If these core parameters could be obtained in a very short time, the optimal fuel reloading patterns would be found more effectively and quickly. A very fast core parameter prediction system is developed using the backpropagation neural network. This system predicts the core parameters several hundred times as fast as the reference numerical code, within an error of a few percent. The effects of the variation of the training rate coefficients, the momentum, and the hidden layer units are also discussed.

ISSN:0029-5639    

DOI:10.13182/NSE93-A23994

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractRigorous tests of the Monte Carlo transport code MCNP have been performed by measuring the efficiency of a6Li-glass moderating neutron detector using Lucite as the moderator relative to the efficiency of the detector using mineral oil as the moderator, and comparing this with the MCNP predicted value. The tests were done using both252Cf fission-source neutrons and 1.2-MeV neutrons produced by a Van de Graaff accelerator.

ISSN:0029-5639    

DOI:10.13182/NSE93-A23995

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractAntiprotons are negatively charged protons that continuously slow down in matter until they are stopped and captured on the surface of a nucleus by a proton; in which case, both proton and antiproton annihilate into gammas, pions, and other short-lived particles. When an antiproton annihilates at rest on the surface of an actinide nucleus, such as uranium, many fragments and neutrons are also produced, following direct reaction, nuclear evaporation, and fission processes, along with production of high-energy gammas and pions. Collectively, these processes have been termed antiproton fission, for simplicity, because many neutrons are produced as the end result of all reactions. Recent experiments at CERN suggest that as many as 15 to 20 neutrons are emitted following antiproton annihilation on238U, that their distribution is peaked near 5 MeV in energy, and that a sizeable fraction (45 to 75%) of the annihilation energy (1.88 GeV per annihilation) is deposited locally in the23SU. A fit to the experimental neutron spectrum of Angelopoulos et al. is presented, and the systematics of transporting and annihilating antiprotons in a multigroup representation are investigated for the first time. Applications of antiproton transport and fission in small spherical assemblies are discussed and contrasted, mainly systematics of local and nonlocal antiproton annihilation, criticality, and disassembly.

ISSN:0029-5639    

DOI:10.13182/NSE93-A23996

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE93-A23997

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE93-A23998

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor