Journal of Nuclear Energy最新文献

A nonlinear analysis of xenon-temperature controlled nuclear reactor dynamics is presented. The set of equations in question belongs to a general class of rate equations with quadratic nonlinearities. Boundedness of the solutions is examined. The mean value of periodic solutions for the flux is shown to be always less than the equilibrium value. The Bogoliubov's method of averaging as extended by Case is applied to obtain approximate solutions. The mechanism of the existence of relaxation oscillations in the linear stability region is analyzed. Computer calculations are performed and found in good agreement with the approximate solutions obtained by means of the method of averaging.

Evidence from a broad range of clean, benchmark experiments has been used to assess the performance of ‘best’ available theoretical methods and differential data for predicting integral thermal reactor properties such as reactivity and reaction rate ratios. It is shown that for improving the consistency of calculated integral parameters for D₂O, H₂O and graphite moderated, uranium fuelled systems, significant modifications to certain currently used nuclear data are desirable. Along with changes in moderator scattering cross-sections, ²³⁸U resonance data and the ²³⁵U fission energy spectrum, some modification of ²³⁵U thermal data has been made which lies within the experimental uncertainties of differential measurements. The ‘new’ data options have been used in various analyses with the WIMS lattice code, and results are presented for the benchmark studies and also for some lattices with more complicated geometries. It is shown that the preferred data generally gives more consistent results for both reactivities and reaction rate ratios over a wide range of conditions, than any previously considered data combinations.

Absolute (n, γ)-cross-sections of some fission products with high yield have been measured. In addition, Fe has been studied to remove some unexplained discrepancies in earlier cross-section measurements. Both, the γ- and the neutron-detector have been calibrated absolutely, so the values derived here had not to be normalized to some other n, γ-cross-sections but rely on the 1/v-dependence of the ¹⁰B(n, α) ⁷Li- and the thermal Au-cross-section only.

The decay λ of a burst of neutrons in a plane lattice with symmetric multilayered cells is computed in a P_N multigroup theory versus the geometrical buckling k. For that purpose, the transport eigenvalue problem is transformed by Vladimirov's symmetric decomposition, and the space variable is eliminated by integration in each layer along the unit cell and by use of Bloch's theorem as boundary condition. A transmission operator for the unit cell generates a generalized eigenvalue problem defining numerically function λ(κ). Generalized Nelkin's coefficients ate computed for various water-beryllium lattices and compared to those obtained for the volume homogenized lattices.

This paper describes a series of integral pulsed neutron experiments performed in a 0·4 × 0·4 × 0·4 m³ metallic thorium assembly in such a way as to allow direct comparison of space independent reaction rates with calculated reaction rates derived from a code which uses the asymptotic reactor theory approximation to describe leakage. The technique relies on the Fourier decomposition of measured space-time dependent reaction rates and the extraction from these of the reaction rate corresponding to the fundamental three-dimensional Fourier spatial mode. The reaction rates measured were the fission rates of ³³⁵U, ²³⁹Pu and ²³⁷Np following a short ∼ 10 ns) burst of neutrons with a mean energy of ∼ 2·7 MeV.