摘要:

Continuous slowing-down theory is generalized so that inelastic scattering can be accurately taken into account. The basic idea underlying generalized theory is the assumption that the ratio, R(u), of the solution spectrum to a reference spectrum, g(u), varies linearly with the lethargy, u; that is, R(u) can be approximated by two terms of a Taylor series as long as g(u) is chosen reasonably. Such conventional theories as Geortzel-Greuling (GG) or Stacey’s improved-GG are included in this theory by taking g(u) as 1/∑s,i(u) or 1/∑t(u), respectively. The present theory is demonstrated to yield quite accurate results for the neutron spectra and coarse-group effective cross sections in many varieties of core and blanket compositions of fast reactors, using three alternative prescriptions for g(u).

ISSN:0029-5639    

DOI:10.13182/NSE75-A26749

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

The transport and diffusion equations are developed in toroidal geometry, with the torus exhibiting a general elliptical cross section. These equations are presented in two different coordinate systems, each of which has its own advantage. It is shown that the elliptical toroidal diffusion equation can be cast into the standard r -θcylindrical equation by appropriately redefining the interaction cross sections and external source. This suggests a“geometric transport correction”—a geometric modification to the r -θcylindrical transport equation which accounts for both the toroidal and elliptical character of the system.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26750

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

The transfer matrix method is applied to energy-dependent neutron transport problems for multiplying and nonmultiplying media in one-dimensional plane geometry. Experimental cross sections are used for total, elastic, and inelastic scattering and fission. Numerical solutions are presented for the problem of a unit point isotropic source in an infinite medium of water and for the problem of the critical235U slab with finite water reflectors. No iterations were necessary in this method. Numerical results obtained are consistent with physical considerations and compare favorably with the moments method results for the problem of the unit point isotropic source in an infinite water medium.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26751

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

A generalization is made of a previous phase-space finite element approximation of the second-order form of the one-group, two-dimensional neutron transport equation in x-y geometry. Three angular approximations are formulated and compared: continuous piecewise bilinear finite element, piecewise constant finite element, and discrete ordinate. These are incorporated into a unified formalism of discrete ordinate-like equations, enabling the spatial variables to be treated identically using piecewise linear or bilinear finite elements. The resulting equations are solved iteratively by a weighted conjugate gradient method in an improved version of the computer code FENT. Numerical and analytical comparisons of the angular approximations are made, and it is found that both piecewise bilinear and piecewise constant approximations in angle substantially mitigate ray effects. The mitigation is shown to be associated closely with transformation of the hyperbolic discrete ordinate equations to the elliptic operators of the discrete ordinatelike finite element approximations. This transformation is accompanied by the disappearance of the characteristics along the discrete lines of neutron travel, and, hence, by the appearance of physically artificial derivative terms normal to the lines of neutron streaming. These terms grow with the subdomains of the angular finite elements.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26752

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractA method of Monte Carlo fitting is described that was used at the transient reactor test facility (TREAT) to calculate the ratio of energy deposition within an experimental fuel pin in a containment loop to the energy deposition at the peak power position in the reactor. The results of the Monte Carlo fitting are compared to experiment and to results of a direct Monte Carlo calculation, with good agreement.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26753

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractMeasured integral quantities such as keff, central reaction-rate ratios, and central reactivity coefficients for 18 fast critical assemblies were calculated using the ENDF/B-IV neutron cross-section set. The correlations between calculation and experiment using Version IV were then compared to those obtained with earlier cross-section data, specifically, Versions I, II, and III of ENDF/B and the Bondarenko cross-section set. In general, ENDF/B-IV was found to do an excellent job of calculating keff. However, discrepancies between calculation and experiment did exist for both reaction-rate ratios and reactivity coefficients. Of particular interest, the fissile-fuel central-worth discrepancy for plutonium assemblies was found to be∼20%.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26754

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractIn the newer, larger pressurized-water reactor cores, the calculated power distributions are fairly sensitive to the number of neutron groups used and to the treatment of the reflector cross sections. Comparisons between transport and diffusion calculations show that the latter substantially underpredict the reflector albedos in the fast (top) group and that the power distribution is shifted toward the core center when compared to 4-group transport theory results. When the fast-neutron diffusion coefficients are altered to make the transport- and diffusion-theory albedos agree, the power distributions are also brought into agreement.An expression for the fast-neutron diffusion coefficients in reflector regions has been derived such that the diffusion calculation reproduces the albedo obtained from a transport solution. In addition, a correction factor for mesh effects applicable to coarse mesh problems is presented. The use of the formalism gives the correct albedos and improved power distributions.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26755

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractThe average neutron density and the average delayed-neutron precursor density for a neutron-multiplying system have been calculated assuming the reactivity to be a two-valued Markov process. The resulting values are shown to be stable for asymptotically long times in agreement with the conclusions of Williams.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26756

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE75-A26757

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE75-A26758

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor