Measured and calculated fission-product poisoning in neutron-irradiated uranium-233

Samples of $sup 233$U and of natural thorium have been irradiated in high neutron-flux facilities, in both soft and hard neutron spectra, and for both short and long exposure times. Included are exposures resulting in depletions of more than 90 percent of the $sup 233$U in the fissile material and burnups of more than 30,000 MWd/MT in the fertile material. Fission-product poison cross sections in two energy groups (thermal and epithermal) exhibit differences between measurement and calculation that are believed to be attributable to a lack of adequate information on important fission products in the literature. Experimental results for transient absorbers in irradiated $sup 233$U give at least 20,000 b for the neutron absorption resonance integral of $sup 149$Pm. This is a factor of 15 higher than that obtained by a 1/v extrapolation of the thermal cross sections. For transient $sup 135$Xe, the measured absorption is 7.5 percent higher than that calculated using ENDF/B-IV data. Information is also provided concerning such matters as fission yields and neutron absorption of neodymium isotopes, the existence of significant transient fission-product poisons other than $sup 135$Xe and $sup 149$Sm, and the shielding of $sup 233$U by $sup 232$Th. Such shielding suggests the need formore » a change in the energy dependence of the $sup 232$Th thermal-neutron cross section. (auth)« less