“…Besides, some methods need a vast footprint, and some are only suited for nuclear systems with regular shapes, which eliminates the MC method's advantage in free 3D modeling. The second kind is independent of space meshing, including the Wielandt's method (Yamamoto and Miyoshi, 2004;Brown, 2007;She et al, 2015;Pan et al, 2022c), the superhistory method (Brissenden and Garlick, 1986;She et al, 2015;Mickus and Dufek, 2018;Pan et al, 2022c), the neutron population growth method (Mickus and Dufek, 2018;Pan et al, 2022a), and the source extrapolation method (Pan et al, 2022b). Wielandt's method is based on the shifted inverse power method (Bronson et al, 2013).…”