A Point-Kinetics Approach to Sensitivity Study of Fast Reactor Dynamic Behavior and Delayed Neutron Spectra

The method of point reactor kinetics in conjunction with the new concepts of delayed spectrum factor and beta growth factor is used to calculate the sensitivity of the dynamic behavior of a fast breeder reactor to large changes in delayed neutron energies following postulated reactivity accidents. The positive ramp rates are introduced not to simulate physical possibilities but solely to test the sensitivity to delayed neutron spectral changes under different conditions. A limited number of transient calculations are made using the point-kinetics code SENSTVTY, six precursor groups, and Doppler feedback. The calculational method and the reactor model are described. Delayed neutron requirements in reactor dynamics are discussed, and a brief review of the sensitivity studies is presented. The results of the sensitivity calculations indicate that the relative power, the peak power, and the accident energy release are sensitive to changes in β_eff resulting from uncertainty in the delayed spectral data, but the sensitivity of the relative power is much greater than the peak power and the accident energy release. The spread in the maximum reactivity reached is found to be ∼18%, and the time spread in the melting of fuel and cladding is in milliseconds.