Effective resonance levels

Abstract

A method based on the use of effective resonance integrals or group cross sections with resonance self-shielding factors has come into extensive use in calculations of resonance absorption in homogeneous systems. An attempt is made to extend the subgroup treatment, which was initially formulated for the region of forbidden resonances, to the allowed region as applicable to heterogeneous media. A method based on the model of equidistant levels with identical parameters has been developed for the region of the forbidden resonances. Two models are presented; one is based on the theory of intermediate resonances with a temperature dependence. Both models are suitable for describing resonance absorption in both homogeneous and heterogeneous media. Test calculations were made for eight uranium-water cells which demonstrated that by using effective resonance levels for U 238 one can attain the accuracy that is at present attainable in calculations according to the parameters of levels and determined by the error of measurement of the parameters and the error of integrated experiments. The method considered can find application in calculations of resonance absorption in the cells of a reactor according to programs oriented for the use of universal constants, which the parameters are.