Capturing and utilizing the random feature in Monte Carlo fission source distributions

•Three mesh-free SW-based methods are proposed to capture the FSD random error term’s 1m feature.•A mesh-free source convergence auto-diagnosis algorithm is introduced utilizing the 1m feature.•The algorithm can automatically save 58% to 81% of the computational time to reach a converged fission source in models with a dominance ratio of around 0.99.