Uncertainty evaluation of effective delayed neutron fraction beta(eff) of typical proto-type fast reactor

Uncertainty of effective delayed neutron fraction beta(eff) is evaluated in terms of three quantities; uncertainties of the basic delayed neutron cons tants: energy dependence of delayed neutron yield nu(d)(m) in the lon energ y side below about 50 keV and in the high energy side above about 4 MeV; an d the uncertainties of the fission cross sections of fuel elements. The unc ertainty of beta(eff) due to the delayed neutron yield is expressed by a li nearized formula assuming that the delayed neutron yield does not depend on the incident energy, and the energy dependence is supplemented by using th e detailed energy dependence proposed by D'Angelo and Filip. The third quan tity, uncertainties of fission cross section, is evaluated on the basis of the generalized perturbation theory in relation to reaction rate ratios suc h as central spectral indexes or average reaction rate ratios. Sensitivity coefficients of the reaction rate ratios to fission cross sections are obta ined by generalized perturbation code. Resultant uncertainty of beta(eff) i s about 4 to 5%, in which primary factor is the delayed neutron yield, and the secondary one is the fission cross section uncertainty: especially for U-238. The energy dependence of nu(d)(m) systematically reduces the magnitu de of beta(eff) about; 1.4 to 1.7%, depending on the model dependence of vs . nu(d)(m) correlation curve.