Neutron-Spectra Calculations for Radiation-Damage Studies

Fast-neutron spectra have been computed using three different codes: GNU-II, HFN, GEHAPO-S-X. Significant differences in spectra are seen as one uses codes with varying degrees of refinement. GE-HAPO-S-X was chosen for calculating cross section values and testing damage models because of its greater accuracy and wider applicability. The calculations illustrate spectral differences existing at different points in a reactor lattice. The spectra are used to compute relative activation for such fast-neutron flux monitor materials as Ni⁵⁸, Fe⁵⁴, Am²⁴³ and to calculate gross vacancy production using widely varying damage models. From the results it is concluded that calculation of spectra in irradiation facilities is necessary for the proper reduction of monitor activities to neutron exposures and for correlation of observed radiation effects in materials irradiated in dissimilar facilities.