Development of a chemistry system code for LBE cooled nuclear systems

SCK•CEN Mentor

Marino Alessandro, amarino@sckcen.be, +32 (0)14 33 80 11

Expert group

Conditioning and Chemistry Programme

SCK•CEN Co-mentor

Van den Eynde Gert , gvdeynde@sckcen.be , +32 (0)14 33 22 30

Introduction

The coolant chemistry control is one of the main technologies for a safe operation of lead bismuth eutectic (LBE) cooled nuclear systems, such as MYRRHA.

In particular, chemical interaction between oxygen and other dissolved impurities in LBE (e.g. impurities generated by corrosion of steels), may lead to the formation of solid oxide particles that are then transported in the primary circuit of the reactor. The continuous deposition and/or accumulation of oxide particles may cause blockages in narrow channels such as those of heat exchangers or fuel assemblies

A theoretical and experimental knowledge on the main chemical processes occurring in LBE have been acquired at SCK-CEN in the recent years, which has led to the development of thermo-chemical models encompassing many species that can occur in MYRRHA. These models, based on the Gibbs free energy formulation, enabled to evaluate the chemical equilibrium concentration of the different species.

The chemical equilibrium between the different species depends on the local temperature of the LBE and the local concentrations of the species. To assess oxide formation and transport  in more detail, LBE equilibrium chemistry should be thus coupled with the temperature and flow fields in MYRRHA with a suitable numerical tool.

CFD models of impurities mass transport in LBE have been successfully developed and applied for the detailed design of components and for steady state analysis of local phenomena [2], [3], [4]. However, due to the high computational cost of CFD methods, these tools are still not fully applied for long term transient analysis on the full reactor system, which is required for the safety analysis and licencing process of MYRRHA.

On the other hand, the development of a 1-D code able to combine thermal hydraulics and LBE chemistry is an invaluable opportunity to fill the gap between theory and application.

Objective

The goal of this thesis is to develop a 1-D thermal hydraulic code which also includes the main chemical processes occurring in LBE systems, at minimal computational cost.

Examples of in-house system codes for transport and chemical reactions of species in liquid metals (e.g. corrosion product species) are available from Russian experience [5], so a starting point exists. Similar codes have been also developed for PWR analysis [6]. In the first part of the thesis a literature review of the aforementioned codes is required in order to acquire the necessary theoretical knowledge for the appropriate mathematical formulation of the problem.

Then, the work will focus on the code development.

In a first approximation it can be assumed that the concentration of the different species will not influence the flow and temperature fields (one-way coupling approach). Hence, the flow and temperature fields (steady state conditions for normal operation or even time-dependent flow and temperature fields in case of transient studies) can be pre-calculated.  The first main objective is to provide a suitable tool for the resolution of flow and temperature fields over a computational domain. Appropriate spatial and time discretization methods should be defined at this stage.

In a second stage, species mass transport should be also included, taking into account the proper boundary conditions.

If time will allow, a latest step could involve the formulation of species relaxation to their chemical equilibrium, based on Gibbs free energy minimization.

A preliminary application and validation of the developed code could be applied to existing LBE loops such as MEXICO, where the combined effect of LBE chemistry and thermal hydraulics can be measured.

 

References

[1] A. Aerts et al., "Oxygen-iron interaction in liquid lead-bismuth eutectic alloy", Physical Chemistry Chemical Physics, a journal published by the Royal Society of Chemistry, 18 (2016) 19526-19530.

[2] A. Marino et al., "Numerical modeling of oxygen mass transfer from PbO spheres packed bed to liquid lead bismuth eutectic: A venturi-type PbO mass exchanger", Nuclear Engineering and Design, 265 (2013) 567-581.

[3] A. Marino et al., "A mass transfer correlation for packed bed of lead oxide spheres in flowing lead-bismuth eutectic", Int. Journal of Heat and Mass Transfer, 80 (2015) 737-747.

[4] A. Marino et al. “Numerical modeling of impurities mass transfer in a wire wrapped fuel assembly under flowing lead bismuth eutectic”, Journal of Nuclear Materials, 2018.

[5] E. V. Usov et al. " Modeling of oxide layer formation and corrosion products coagulation and transport in lead coolant using the OXID module of the HYDRA-IBRAE/LM code, Atomic Energy, 122 (2017).

[6] M. Benfarah, et al.  "PWR circuit contamination assessment tool. Use of OSCAR code for engineering studies at EDF," EPJ Nuclear Science and Technology, 2 (2016).

The minimum diploma level of the candidate needs to be

Academic bachelor

The candidate needs to have a background in

Informatics , Mathematics , Chemistry

Estimated duration

six months