We analyze k-α iteration method for α eigenvalue problems, and point out that parameter in k-α iteration method affects error estimation of alpha eigenvalues, while error estimation has no relationship with the parameter. If the parameter isn't given properly, the estimated error deviates the real error estimation. Estimated error given by MCNP4C may deviates from real error estimation due to improper parameter. A parameter selecting method called average neutron fission lifetime method is proposed to make estimated error and real error estimation equal strictly in mathematics. It was tested with numerical experiments.

Flux field calculation in time-dependent problems with Monte Carlo method and associated particles transportation equation are described.The random walk principle of time station sampling(TSS) method in dynamic system is introduced.A time station importance sampling(TSIS) method is developed and applied to decrease statistical fluctuation in global flux field calculation.Alternative importance function and its unbiased weight of modification are investigated.Numerical results and analyses on methods in specific model are given.The time station importance sampling(TSIS) biased method can be used to control statistical variance of global fine mesh flux adaptively in a same level.

Some successful applications of MCNP code are introduced for the nuclear critical safety, techneque research for nuclear safeguards, and neutron slowing-down install simulation. Developments of this code for these applications are desovibed. A brief discussion is made about necessary development for future applications as well.