Angle Spectral Calculation of Surface Flux by Functional Expansion Tally in Monte Carlo Simulation

The traditional Monte Carlo simulations use tally bin to calculate angle spectral of surface flux. The tally bins must be sufficiently small to obtain detail shape of angle spectral, but the small bins result in large statistical errors. The function expansion tally (FET) is a method that uses a Monte Carlo simulation to estimate expansion coefficients of the tally distribution with respect to a set of orthogonal basis functions. In this paper, the FET method was used to calculate angle spectral of surface flux. This method can construct functional estimates of angle spectral.