Journal of Nuclear Energy最新文献

An integral transport theory method is described for calculating the flux distribution in an infinite, rectangular lattice, assuming mono-energetic neutrons and isotropic scattering. Important features of the method are: the rectangular cell boundary is treated exactly and the contribution of the surrounding cells to the reference cell is included explicitly.

The method is implemented in a computer program, CELTIC, and a description is given of the numerical techniques used by the program to solve the singular integral equation. The convergence and accuracy of CELTIC is assessed by a comparison with exact analytic results which are obtainable for the spatially constant cross section case.

Fluxes and disadvantage factors for the well-known Thie lattices are computed by CELTIC and compared with the results obtained by previous workers who used various transport techniques most of which rely on the cylindricalized cell approximation. The increase in accuracy resulting from the use of ‘White’ boundary conditions rather than the reflecting boundary condition in the cylindricalized cell is demonstrated.

The variation of the disadvantage factor, ξ, as a function of the cell volume/fuel volume ratio is studied as the cell width decreases until the fuel region becomes the inscribed circle, for the case that the neutron cross sections remain unchanged. A minimum in the ξ curve is found, which confirms the result obtained in a previous paper which, however, assumed spatially constant neutron cross sections in the square cell.

The amplitudes and phases of neutron waves have been measured in a BeO assembly in the frequency range 515·7 Hz to 1719 Hz. The results confirm earlier measurements that below ∼520 Hz the neutron wave has the properties of a discrete mode of propagation. At frequencies ≧720 Hz the attenuation α(z) and phase shift parameters ξ(z) change with distance from the source, the change being more marked the higher the frequency.

The observed spatial variations of α(z) and ζ(z) do not agree with present theoretical predictions. Interference effects predicted by theory have not been observed.

A study of the diffusion length of neutrons in an infinite lattice of alternate slabs of two different materials in the direction parallel to the slabs has been carried out on the basis of integral transport theory. In the one-velocity approximation we obtain, numerically, curves for aluminium water lattices from which one can observe the possibility of the existence or non-existence of a discrete decay constant ν for a given configuration.

In the energy dependent case, two of the configurations studied by Palmedo and Conant have been chosen, and it has been shown that neither of them possesses a discrete decay constant, which is consistent with their experimental findings. The asymptotic spectra in the aluminium and water regions for certain configurations have also been discussed. Calculations are also made for the lead-water systems studied experimentally by Mukhin et al. and satisfactory agreement obtained.

Angular differential number and energy albedo were measured at a scattering angle of 60° for narrow beam of ¹³⁷Cs gamma rays normally incident on finite thickness scattering media of various atomic numbers. Measurements were made using a collimated 3 cm³ Ge(Li) detector with suitable electronics and a 400 channel pulse-height analyzer. The calculation of the energy spectrum of the scattered photons was carried out by using a response matrix with 51 energy intervals over the range 0·04−0·3 MeV.

The analysis developed in an earlier paper is applied to a small highly enriched homogeneous fast reactor to evaluate the critical mass of ²³⁵U. Numerical results indicate that the energy-dependent buckling analysis gives superior results to the conventional constant-buckling approach, particularly for the fundamental mode approximation. For the fast system investigated the best choices of constant buckling are obtained by selecting from those energy regions with atypically low leakage and high reactivity importance.

Elastic neutron scattering cross sections of ²³⁹Pu are measured at ⪅50 keV intervals from 0·3−1·5 MeV with incident neutron resolutions of ≈20 keV. Total neutron cross sections are measured from 0·65 to 1·5 MeV at intervals of ⪅5 keV and with resolutions of ≈2·5 keV. The experimental results are compared with the predictions of optical- and statistical-models, with other measured values and with representative evaluated data.