Development of the capability for multi-group shielding library generation in the nuclear data processing code NECP-Atlas

The capability to generate multi-group shielding library is developed in the nuclear data processing code NECP-Atlas. To make the code suitable for the applications in different types of reactors, several improvements are made in the code, such as the resonance self-shielding method and energy-group structure optimization. The hyperfine group method is applied to perform resonance self-shielding calculations for different configurations. The energy-group structure optimization method is developed based on the contributon theory to enhance the calculation accuracy of the thermal neutron flux and photon flux. The accuracy of the newly developed capability is verified with the reference results calculated using BUGLE-B7 libraries. Two libraries with optimized neutron energy-group structures of 47 groups and 60 groups are obtained based on the contributon theory. Numerical results show that the thermal neutron flux and photon flux calculated based on the two libraries are greatly improved.