Optimised Iteration in Coupled Monte Carlo – Thermal-Hydraulics Calculations

¹ Delft Nuclear Consultancy, IJsselzoom 2, 2902 LB Capelle aan den IJssel, The Netherlands
² KTH Royal Institute of Technology, Division of Nuclear Reactor Technology, AlbaNova University Center, 10691 Stockholm, Sweden

Abstract

This paper describes an optimised iteration scheme for the number of neutron histories and the relaxation factor in successive iterations of coupled Monte Carlo and thermal-hydraulic reactor calculations based on the stochastic iteration method. The scheme results in an increasing number of neutron histories for the Monte Carlo calculation in successive iteration steps and a decreasing relaxation factor for the spatial power distribution to be used as input to the thermal-hydraulics calculation. The theoretical basis is discussed in detail and practical consequences of the scheme are shown, among which a nearly linear increase per iteration of the number of cycles in the Monte Carlo calculation. The scheme is demonstrated for a full PWR type fuel assembly. Results are shown for the axial power distribution during several iteration steps. A few alternative iteration method are also tested and it is concluded that the presented iteration method is near optimal.