Some Monte Carlo Techniques for the Calculation of Doppler Coefficients

A Monte Carlo method for the analysis of the Doppler effect has been developed which employs special perturbation techniques to compute effects due to changes in both the temperature and the diameter of fuel rods. These techniques facilitate the application of Monte Carlo to this type of problem and make possible the elimination of approximations inherent in earlier analytic and numerical methods. Numerical results obtained by this method are in good agreement with previously reported measurements on ZPR-III. The method has been applied to the study of the effect of fuel diameter on the Doppler coefficient in a typical fast reactor. Reducing the fuel diameter in a sodium-cooled uranium-carbide reactor from 0.30 to 0.15 cm was found to increase the Doppler coefficient 13%.