OPTIMISATION OF MONTE CARLO BURNUP SIMULATIONS

Jan Dufek,Ignas Mickus

doi:10.1051/epjconf/202124704016

Abstract

We show here that computing efficiency of Monte Carlo burnup simulations depends on chosen values of certain free parameters, such as the length of the time steps and the number of neutron histories simulated at each Monte Carlo criticality run. The efficiency can thus be improved by optimising these parameters. We have set up a simple numerical model that made it possible for us to test a large number of combinations of the free parameters, and suggest a way to optimise their selection.

Highlights

It has become a common practice for users of Monte Carlo burnup codes to use relatively large time steps of several weeks or months because this helps to reduce the number of executions of the Monte Carlo criticality and depletion solvers
Test results suggest that efficiency of Monte Carlo burnup simulations may be maximised when the fraction of the cost of all depletion calculations in the overall cost of the whole Monte Carlo burnup simulation, x, is inside a certain interval that we approximately evaluated to be (0.2, 0.8)
We wish to note that the numerical model used in this study was rather very simple, and the range of optimal values of x may be somewhat different in real Monte Carlo burnup simulations

Summary

INTRODUCTION

It has become a common practice for users of Monte Carlo burnup codes to use relatively large time steps of several weeks or months because this helps to reduce the number of executions of the Monte Carlo criticality and depletion solvers. The choice of the length of the time step represents an optimisation problem We study this problem here and suggest a way to optimise the user-defined free parameters. A user choice of the number of neutron histories simulated at each Monte Carlo criticality calculation is, related to the optimisation of the length of the time steps when the total computing cost of the whole Monte Carlo burnup simulation is assumed to be given. Reducing the number of neutrons per criticality run makes it possible to increase the number of time steps In such a case, neutron flux will be computed with larger random (statistical) error; the random error will not propagate as much into the fuel depletion thanks to the short time steps.

NUMERICAL MODEL

NUMERICAL TESTS

DISCUSSION AND CONCLUSIONS