Development of a module to generate delayed photon data in ACE format within nuclear data processing code NECP-Atlas

This study develops a module to generate delayed photon data in ACE format, in the nuclear data processing code NECP-Atlas. In this module, the emission of delayed photons from fission products is treated as a specific neutron-reaction, and the delayed photon production cross section and the energy distribution data are calculated with the fission yield sub-library and decay sub-library of evaluated nuclear data libraries. The accuracy of the module is verified through a one-dimensional sphere problem and a fast reactor problem. Finally, the study analyzes the influence of delayed photon on heating distributions of the lead–bismuth fast reactor SVBR and the graphite moderated molten salt reactor MSBR. The results demonstrate that the delayed photon can contribute up to 11.2% of the heating of the reflector assemblies in SVBR, and contribute approximately 24% to the heating of graphite moderator in MSBR.