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 vd is one of the principal sources of uncertainty in predicting the fission reactor reactivity scale βeff. The current uncertainties in the dependence of vd on incident neutron energy is investigated for significance in the evaluation of βeff. 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 vd, and these would result in variations of up to ∼2% in the value of βeff for a typical liquid-metal fast breeder reactor.