Development of Delayed Photon Group Parameters for Estimating Delayed Photoneutron Kinetics Parameters

In a previous study, a kinetics parameter estimation method for the coupled neutron-photon point kinetics model in Monte Carlo eigenvalue calculations was suggested. Although the underlying physics, namely that delayed photoneutrons originate from delayed photons, was already incorporated in the previous formulation, the lack of parameterized delayed photon data limited its practical application. This work develops delayed photon group parameters to enable the estimation of delayed photoneutron kinetics parameters. The per-fission delayed photon emission data are generated using independent fission yields, decay data, and photon emission libraries in SCALE/ORIGEN, and verified against existing CINDER-based data reported by Sandia National Laboratories. Subsequently, 11-group delayed photon parameters are obtained by fitting both the time-dependent multiplicity rate and spectra across 48-group energy bins. The developed 11-group delayed photon parameters are applied to a CANDU-37 fuel lattice problem, showing good agreement in delayed photoneutron yield and multiplicity rate decay curves under single fission pulse and long irradiation conditions. These results validate both the developed delayed photon group parameters and the applied kinetics parameter estimation method.