CODES

Han Gyu Joo, Gwan Young Kim, Leonid Pogosbekyan, “Subgroup Weight Generation Based on Shielded Pin-Cell Cross Section Conservation,” Annals of Nuclear Energy, 36,859-868 (2009).

The multigroup(MG) cross section(XS) generation code EXUS was developed at SNU RPL in order to generate directly the MG XSs from the evaluated nuclear data files(ENDF). It does not require any pre-generation of cross section data. Its calculation procedure consists of five steps : 1) the Doppler broadening processing by the NJOY routines, 2) the consideration of the self-shielding effect, 3) the calculation of the fission and the scattering transfer matrices, 5) the multigroup spectrum calculation. EXUS uses the ultrafine group structure for the transport calculation to resolve the self-shielding and the resonance interference effects properly.

In the ENDF system, resonance XSs are represented in the form of the resonance parameters instead of the pointwise XSs. Therefore the reconstruction process based on the resonance parameters should be performed. The Doppler broadening effect should also be considered for a given temperature and it can be performed with the reconstruction work. It is not simple to realize the reconstruction and Doppler broadening feasibilities in EXUS and thus the NJOY routines which are widely used for the ENDF processing, was integrated in EXUS.

In order to consider the anisotropic scattering effect, high order moments of the MG scattering transfer matrix should be required. They are calculated based on high order moments of neutron spectrum. For this reason, the extended transport approximation is introduced for 0-dimensional problem. The extended transport approximation assumes that the number of neutrons scattered into an energy group g is the same as the number of neutrons scattered out from the group for n > 1.