Shifting study of a VHTR using reprocessed fuel with various TRISO packing fractions

A simplified VHTR (very high temperature reactor) loaded with a mixture of depleted uranium and transuranics (TRUs) fuel was analyzed changing the TRISO packing fraction (pf), i.e., the TRISO kernel radius. Five cases were simulated and evaluated during 900 days with a burnup of 92,700.0 MWD/THM without reloads. The effective multiplication factor (keff) and the fast/thermal flux ratio at zero and full power, fuel temperature coefficient (αTF), moderator temperature coefficient (αTM), and fuel composition at BOL (begin of life) and EOL (end of life) were analyzed. Overall, the results show that transuranics elements from reprocessed fuel of PWRs spiked with depleted uranium (0.2% 235U) to obtain 15% LEU-fuel (235U, 239Pu and 241Pu) can be used as fuel in VHTR. The calculations were carried out with the Winfrith Improved Multi-Group Scheme (WIMSD5) code and the ENDFB65 cross-section data (Askew et al., 1966; Leszczynski, 1990).