Time step length versus efficiency of Monte Carlo burnup calculations

• Time step length largely affects efficiency of MC burnup calculations.
• Efficiency of MC burnup calculations improves with decreasing time step length.
• Results were obtained from SIE-based Monte Carlo burnup calculations.

We demonstrate that efficiency of Monte Carlo burnup calculations can be largely affected by the selected time step length. This study employs the stochastic implicit Euler based coupling scheme for Monte Carlo burnup calculations that performs a number of inner iteration steps within each time step. In a series of calculations, we vary the time step length and the number of inner iteration steps; the results suggest that Monte Carlo burnup calculations get more efficient as the time step length is reduced. More time steps must be simulated as they get shorter; however, this is more than compensated by the decrease in computing cost per time step needed for achieving a certain accuracy.