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Modified One-Mode Method for Fast-Reactor Diffusion Calculations

Takashi Kiguchi

Nuclear Science and Engineering

Volume 53 / Number 1 / January 1974 / Pages 112-120


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The modified one-mode method for fast-reactor neutron diffusion calculations was formulated by collapsing two- or three-energy-mode synthesis equations to an effective one-mode equation. The calculational procedure consists of solving an eigenvalue problem to determine the effective neutron multiplication factor and the first-mode expansion coefficient, and solving inhomogeneous problems to determine the higher mode expansion coefficients. Therefore, the computer running time nearly equals that of the conventional one-group eigenvalue problem. The accuracy of this method was investigated by comparing the results obtained by a modified one-mode method with reference 26-group calculations, employing a one-dimensional radial model of a commercial fast breeder reactor. The discrepancies between the modified one-mode method based on three-mode synthesis and the 26-group method are <0.1% in the effective multiplication factor, 5% in the control-rod reactivity and <2% in the power distribution. These results assure the applicability of this method to fast-reactor design studies.

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