Title: CALCULATIONS OF k FOR SOME SMALL U$sup 233$-, U$sup 235$-, AND Pu$sup 239$- FUELED FAST REACTORS

The effects of uncertainties of nuclear data on the calculation of integral quantities for some fast breeder systems were evaluated. The integral quantities chosen were reactivity, initial breeding ratio, and initial internal breeding ratio. The fuels chosen were Pu/sup 239/-U/sup 238/, both as metal and oxide, and U/sup 233/-Th as oxide. The importance of propagation of errors on the uncertainty in reactivity was determined. Results indicated that because of inaccuracies in the values of nuclear parameters as known within the present state of the art'' the deviations of the calculated reactivities should be about, and possib1y larger than, 2% DELTAmore » k/k for all the medium and large systems considered. The deviation of the initial breading ratio is 3.5%, and for the initial internal breeding ratio it is about 5%. The consequent uncertainty in the calculated critical mass is of the order of 4%. (M.C.G.)« less

The near-equilibrium energy spectra of the delayed neutrons associated with fast-neutron-induced fissions of /sup 232/Th, /sup 233/U, /sup 235/U, /sup 238/U and /sup 239/Pu are reported over the energy range 30 keV to 1500 keV. The fission source spectrum approximated a prompt fission spectrum. A significant fraction of delayed neutrons were found to exist at energies below 100 keV and peaks in the spectra are in agreement with peaks reported by others. Comparisons with existing measurements show agreement at energies above 150 keV but have significant differences at energies below this value.