Contribution to study of Dancoff effect in cylindrical systems

This paper deals with the affect od spatial interference between fuel elements and its influence on the resonance integral. General relation for correction of shielding dependent on the first collision portability was derived. Usual assumption about totally black resonance absorber was not taken into account and spatial distribution of elements was random. Shielding effect for two rods and self-shielding effect of tube was studied in detail. Analysis of standard Dancoff problem shows that the shielding correction function is dependent on all resonance parameters, temperature, size of rods and their mutual distance and properties of the moderator. Proposed method is based on the assumption of flat fluxes which enable analytical determination of first collision probability. Influence of interference scattering was taken into account afterwards and was not treated directly. System of balance equations was solved by applying IR approximation. In order to enable easier numerical calculation of shielding correction significant simplification of obtained results was done by applying P-L approximation of Bonaloumi. Obtained numerical results show good agreement with values obtained by applying Hellstrand empirical relation for resonance integral. A simple procedure is proposed for redefining some parameters and Asiu equations which enable more precise determination of transparency coefficient of tube element