Annals of Nuclear Science and Engineering最新文献

In the present paper characteristics of fast reactors with simultaneous using of uranium-235 and plutonium in the core are considered. Joint using of uranium and plutonium fuels in a reactor is shown to result in a considerable effect both in flattening of the heat-generation field and in its stabilization. As a result a considerable increase of the power density removed in combination from uranium and plutonium is achieved.

Transfer function measurements were conducted in the RA-2 zero power reactor assembly using the cross-correlation technique of noise analysis. Perturbations found in the experimental curves did not allow an accurate evaluation of the prompt-neutron decay constant, α_c. The source of these perturbations was found to arise from mechanical vibrations transmitted to the control rods. Dynamically stimulated oscillations induced in both a control rod and small piece of cadmium were analyzed. Their behaviour as compared with results from a reactor model developed from both analog and digital computations; a strong distortion in the power spectral density was found for the control rod oscillation. Reactor responses to sinusoidal reactivities of various amplitudes (0·05–3·00 dollars) and frequencies (0·01–100 Hz) were computed. The inverse problem, i.e., predicting reactor input from a given output, was also studied. Both calculated and measured power spectral densities are shown.

One- and two-dimensional diffusion equations in slab geometry are solved by a method of Fourier expansion. In this method, at first, equations for the fluxes on the boundaries and their normal derivatives are derived. Applying boundary conditions, these equations are solved and all boundary values are determined. Then using these boundary values, the Fourier coefficients of the flux in the region are calculated. Different from the eigenfunction expansion method, the function series used for the expansion is independent of the boundary conditions. Therefore multi-regional problems are also solved by this method. The results of the numerical calculations are given and compared with the results by the usual finite difference method.

The problem of minimal time control of xenon spatial oscillations in nuclear power reactors is investigated and the effect of constraints on the control variable (rod position), spatial offset magnitude and rate of change, which is closely related to the rate of change of the local power density, is studied. The concept of spatial offset phase plane is extended to include direct reference to the measured spatial offset. The optimal constrained and unconstrained trajectories and switching curves are analyzed in the phase plane. Work done on the Carnegie-Mellon University digital reactor simulator confirmed the success of the derived theoretical results. Operational strategies that embody both the strength of the theory and the simplicity needed for practical application are recommended.

The heat rejection of power plants to the environment can be reduced by using a binary (bottoming) power cycle which receives its energy input from the primary cycle cooler. High temperature gas cooled reactors with helium turbines are particularly favourable for binary cycle application due to their relatively high heat rejection temperatures and wide temperature range. The feasibility of such cycles was investigated for several working fluids. Their thermodynamic characteristics and estimated efficiency were compared. The results indicate that overall plant efficiencies of 49 per cent are attainable with hydrocarbons and 47 per cent with fluorocarbons (Freons) as working media. The incremental specific costs of the binary system would be substantially less than the cost of current nuclear plants.

The lattice model concept of stochastic gamma ray transport is used to calculate the radial distributions of reflected and transmitted gamma rays on the faces of slabs of different thicknesses from a point collimated incident source. The radial distribution of scattered, reflected and transmitted spectra is calculated and the effect of incident angle, slab thickness, and annihilation radiation on iron and aluminum is investigated. Each collision in the medium is considered to be either a Compton scattering, a photoelectric absorption, or a pair production. To reduce variance; the absorption, point of first collision, and reflection and transmission after each collision are calculated analytically. These calculations are very easily done by associating a weight factor with the gamma rays at each lattice point. When pair production occurs, the history of one photon is followed with the statistical weight doubled. Using the model, a computer code is developed which is called PUGRT1 (Pahlavi University Gamma Ray Transport 1). The results of this code are found to be in good agreement with other calculations and experimental results on iron and aluminum.

The “weighted” phonon frequency spectra developed for U and O in UO₂ by Thorson and Jarvis (1969) are used to deduce the effective temperatures for these two nuclides, and some comments are made on the effect of crystalline binding in UO₂ on the temperature broadening of resonances in uranium.