Uncertainty Evaluation of Effective Delayed Neutron Fraction β_<eff> of Typical Proto-type Fast Reactor

概要

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Uncertainty of effective delayed neutron fraction βeff is evaluated in terms of three quantities; uncertainties of the basic delayed neutron constants, energy dependence of delayed neutron yield νmd in the low energy side below about 50 keV and in the high energy side above about 4 MeV, and the uncertainties of the fission cross sections of fuel elements. The uncertainty of βeff due to the delayed neutron yield is expressed by a linearized formula assuming that the delayed neutron yield does not depend on the incident energy, and the energy dependence is supplemented by using the detailed energy dependence proposed by DAngelo and Filip. The third quantity, uncertainties of fission cross section, is evaluated on the basis of the generalized perturbation theory in relation to reaction rate ratios such as central spectral indexes or average reaction rate ratios. Sensitivity coefficients of the reaction rate ratios to fission cross sections are abtained by generalized perturbation code. Resultant uncertainty of βeff is 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 238U. The energy dependence of νmd systematically reduces the magnitude of βeff about 1.4 to 1.7%, depending on the model of the energy vs. νmd correlation curve.
社団法人日本原子力学会の論文
1999-01-25