Neutron transport numerical simulation of different energy of neutron sources is performed in hypothetical nuclear warhead models.Three methods of actively warhead detection are analyzed and the feasibility of actively detecting warheads with three types of neutron sources is studied.With 14.1 MeV pulse neutron source,distribution of delayed neutron flow with time is studied.Results show that the warheads can be detected without exposing the sensitive information of nuclear weapons by detecting the delayed neutrons.

The nonlinear analytic nodal method require analytic solutions of the two-node problems,in which the numerical instability problem might be encountered due to the ill-conditioned algorithm for finding the particular solution of near-critical node.To address this problem,a stabilization method is developed by applying the method of variation of parameters and linear approximation to the near-critical node calculations.Numerical results demonstrate the effectiveness of the method.

The limitations of various typical flux-Limited diffusion theory and advantage of asymptotic diffusion theory with time absorption constant are analyzed and numerically compared. The conclusions are as follows. Though the flux-Limited problem in neutron diffusion theory are theoretically solved by means of derived flux-Limited diffusion equation, but it's going too far to limit flux due to the inappropriate of the assumption in deriving flux-limited diffusion equation. The asymptotic diffusion theory with time absorption constant has eliminated the above-mentioned limitation, so it is more accurate than flux-Limited diffusion theory in describing neutron transport problem.