Search

Coherent scattering is the theoretical basis of X-ray diffraction, which is widely used in the field of materials. A functional module to calculate the nondestructive testing of photon-atomic and photon-molecular coherent scattering cross sections is developed in the nuclear data processing code NECP-Atlas. The photon-atomic coherent scattering cross section is processed in NECP-Atlas with the same method as that of NJOY2016. In practice, photon interacts with materials which usually consist of numerous polyatomic molecules. Therefore, the photon-molecular coherent scattering cross sections should be calculated instead of photon-atomic coherent scattering cross sections to acquire more accurate simulated results. First, the independent atom model (IAM) was implemented to calculate the photon-molecular coherent scattering cross sections with the assumption that the atom was isolated. This approximation works well when the momentum transfer of incident photons is large. At small momentum transfer, the interference effects of various atoms cannot be ignored. Then, the molecular interference model was introduced to consider the influence on angular distribution of secondary photons due to the interference effects. The molecular interference functions of water and ethanol were simulated using molecular dynamics simulation, and then applied in the ACE library. The atomic form factors of the atoms in water and ethanol molecules were modified by the molecular interference function. To quantify the influence of molecular interference effects on angular distribution of secondary photons, an imaging system was simulated. Numerical results show that the molecular interference effects have a significantly influence on the angular distribution of photons at small momentum transfer, while at large momentum transfer, the molecular interference effects can be ignored.

The nuclear data processing code NECP-Atlas, developed at Xi’an Jiaotong University, has various functions to process the evaluated nuclear data to generate the applied nuclear data library for the nuclear reactor designs. In this paper, the photonrelated data generation capacities were developed in NECPAtlas, including the photon production cross sections and photon irradiation cross sections. In the conventional nuclear data processing code such as NJOY, only the production cross section for the prompt photon released with the neutroninduced reactions, and the photonatom reaction cross section can be produced, while the delayed photon released by the fission products is ignored regardless of its large contribution for the heating of the regions without fissionable materials such as control and reflector assemblies in fast neuron reactors. In this paper, the capacity for the generation of the production cross section for the delayed photon was developed in NECPAtlas. Besides, in the conventional nuclear data processing code, only the neutron irradiation damage cross section can be generated, while in the practical reactors, electron and positron also cause significant irradiation damage. The photonatom reactions, including Compton scattering, pair production and photoelectric effect, emit electron and positron. Therefore, the photon can also cause irradiation damage. To satisfy the demands from various application aspects, the capacity for the calculation of the photon irradiation damage cross sections was also developed in NECPAtlas. Meanwhile, the electron and positron irradiation damage cross section can also be produced, because it is the basis for the calculation of photon irradiation damage cross section. The delayed photon production cross sections were tested on the EBRⅡ fast reactor, and the results were compared with the library of the ERANOS which includes the production cross section of delayed photon. The difference of photon heating calculated based on the two libraries respectively from NECPAtlas and ERANOS is less than 0.93%, which means the correctness of the delayed photon data produced by NECPAtlas. Besides, the numerical results show that if the delayed photon is ignored, the difference of photon heating for the control assembly and reflector assembly can reach 3258% and 2041%, compared with the results of considering the delayed photon. The electron and positron displacement damage cross sections of Fe and Au calculated by NECPAtlas were verified with the results published by Oka Ridge National Laboratory, and the photon displacement cross sections calculated by NECPAtlas were verified with results reported by other researches. The numerical results show good agreement with the reference results.