An iterative scheme to include turbulent diffusion in advective-dominated transport of delayed neutron precursors

TL;DR

This paper introduces an iterative method combining the Method of Characteristics with turbulent diffusion effects to accurately model delayed neutron precursors in advective-dominated flows, validated through a 2D reactor simulation.

Contribution

It develops a novel iterative scheme integrating turbulent diffusion into the MOC framework for DNP transport, enhancing modeling accuracy in turbulent reactor flows.

Findings

The method accurately predicts DNP distributions in turbulent flows.

Turbulent diffusivity significantly affects reactor reactivity.

Validation against finite volume methods confirms the approach's effectiveness.

Abstract

In this study, the Method of Characteristics (MOC) for Delayed Neutron Precursors (DNPs) is used to solve the precursors balance equation with turbulent diffusion. The diffusivity of DNPs, significantly higher than molecular diffusivity, emerges in turbulent flows from the time-averaging of the DNPs mass balance equation. To integrate this effect within the MOC framework, the advection-reaction component of the DNPs balance equation is solved using the MOC, while the diffusive source is computed from the concentration of the previous iteration. The method is validated on a 2D recirculating pipe reactor with high Reynolds number flow, comparing the MOC with diffusion to a standard finite volume (FV) discretization of the fission products balance equation. Additionally, the impact of the diffusivity term on DNP distributions and reactor reactivity is quantified as a function of the turbulent Schmidt number.