Dynamic external source simulation mode

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The dynamic simulation mode allows running external source simulations in sub- and super-critical systems over extended time periods, while keeping the simulated population size within reasonable limits. The methodology is based on sequential population control, as described in a conference paper presented at M&C 2013.[1]

The mode is invoked by linking a time bin structure in the set nps card. The simulation is divided in time intervals, as defined by the bin structure. The size of the simulated population is adjusted at each bin boundary to match the starting population, and the total weight is preserved.

Example MCNP and Serpent inputs from the M&C 2013 paper are provided here. The two calculation cases are:

  1. Fast system (Pu-flattop)
  2. Thermal system (uranium solution in container)

The sub-and super-critical states presented in the paper are invoked by adjusting the reflector thickess (fast system) and surface level (thermal system). The reference MCNP calculations are run in the conventional external source simulation with time cut-off. Serpent inputs include both external source and dynamic modes.


  1. ^ Leppänen, J. "Development of a dynamic simulation mode in the Serpent 2 Monte Carlo code." In proc. M&C 2013, Sun Valley, ID, May 5-9, 2013.