Multi-group effective cross section calculation method for Fully Ceramic Micro-encapsulated fuel

Abstract

A multi-group effective cross section calculation method for Fully Ceramic Micro-encapsulated (FCM) fuels containing stochastically dispersed tri-structural isotropic (TRISO) coated fuel particles is proposed to solve the double heterogeneity (DH). In resonance-energy range, the disadvantage factors are obtained by solving a one-dimensional model containing a TRISO particle with hyperfine group method. The matrix and TRISO particles will be homogenized by correcting the hyperfine-group cross sections with disadvantage factors. Due to the large absorption cross section of heavy isotopes in thermal-energy range, the spatial self-shielding effect in the TRISO particles should also be taken account. In the thermal-energy range, the multi-group disadvantage factors are obtained by the neutron’s first-collision probabilities and penetrating probability equivalent. Based on the methods described above, the materials in the fuel rod are merged into a homogeneous material. The FCM fuel can be treated as traditional PWR lattice. In the present paper, the Dancoff correction factor of every rod is firstly obtained with neutron current method. Then a one-dimensional model for every fuel rod will be established by Dancoff factor equivalent. Finally, the hyperfine group calculation is carried out based on the one-dimensional rod model to get the effective cross sections of each fuel rod. Numerical results show that the proposed method is proved effective to treat DH for FCM fuel and capable of providing accurate effective cross sections.