The Effective Beta Sensitivity to the Incident Neutron Energy Dependence of the Absolute Delayed Neutron Yields

The uncertainty of the ²³⁵U, ²³⁹Pu, and ²³⁸U absolute delayed neutron yields v_d is one of the principal sources of uncertainty in predicting the fission reactor reactivity scale β_eff. The current uncertainties in the dependence of v_d on incident neutron energy is investigated for significance in the evaluation of β_eff. The uncertainty effects on the GODIVA, JEZEBEL, Zero Power Reactor, SNEAK, and Masurca benchmark facility calculations are analyzed using ENDF/B and JEF basic data. Different assumptions about the energy dependence result in variations of up to 5% in the reactor spectrum averaged values of v_d, and these would result in variations of up to ∼2% in the value of β_eff for a typical liquid-metal fast breeder reactor.