Existing experimental data on the variation of reactivity with core geometry are reviewed. Four typical fast neutron systems are analyzed to predict: (l) the variation of critical mass with cylindrical core geometry (core and reflector composition are held fixed); (2) the reactivity worth of fuel at the radial core boundary as a function of cylindrical core geometry; and (3) the geometric variation of heat removal parameters; these include the ratio of: (a) Maximum power density to average power density in the core. (b) Maximum power density to average radial power density in the core. (c) Total reflector power to total …
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Existing experimental data on the variation of reactivity with core geometry are reviewed. Four typical fast neutron systems are analyzed to predict: (l) the variation of critical mass with cylindrical core geometry (core and reflector composition are held fixed); (2) the reactivity worth of fuel at the radial core boundary as a function of cylindrical core geometry; and (3) the geometric variation of heat removal parameters; these include the ratio of: (a) Maximum power density to average power density in the core. (b) Maximum power density to average radial power density in the core. (c) Total reflector power to total core power. The absolute values of all of these parameters are determined by the core and reflector compositions of the four systems. These were chosen to simulate typical constituents of interest to reactor analysis. Two systems represent a typical fast reactor and a typical fast critical experiment. The other two systems represent compositional combinations of the two basic systems. The results of the analyses show that the significant geometric varia tion is in items (2) and (3b). Itenm (1) is almost constant for small variations near the optimum geometric configuration. Outside of this range, the variation of critical mass with core geometry is pronounced. A most significant result shows that the ratio of the spherical critical mass to the minimum cylindrical critical mass (shape factor), for fixed core and reflector composition, depends primarily on core composition. The composition of the thick reflector has a lesser enffect on this ratio which was found to increase with core density. The two-dimensional calculations are interpreted and analyzed on the basis of onedimensional concepts. Reflector savings are calculatend for spherical and cyIindrical systems. The more exact reflector savings determinations are compared with more approximate calculations. It is found that the approximate determinations are qualitatively correct and show correct trends. However, the more detailed and accurate analytical techniques are required for precision comparison between critical mass and core surface area is demonstrated. It was found that, in the range of interest, the critical mass depends almost linearly upon the surface area. The same linear dependence approximates all the systems studied. (auth)
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Loewenstein, W.B. & Main, G.W.FAST REACTOR SHAPE FACTORS AND SHAPE-DEPENDENT VARIABLES,
report,
November 1, 1961;
Illinois.
(https://digital.library.unt.edu/ark:/67531/metadc1059902/:
accessed May 13, 2025),
University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu;
crediting UNT Libraries Government Documents Department.
