Development of condensation models for the application of steam condensation in AGR boilers

Context:
EDF Energy operates the nuclear reactors in the UK. We are also planning to build two new nuclear powers stations at Hinkley Point. The nuclear fleet Advanced Gas-cooled Reactors (AGRs) in the UK is reaching the end of its lifetime. The boilers are a critical part of the plant operation and are subject to ageing and degradation. They have been identified as a potential risk to future operation and in order to be able to anticipate problems, a better understanding of the heat and fluid flow is required.
EDF Energy has been working on the plant life time extension program for the nuclear reactors in the UK for several years. One of the various research areas is the possibility of condensation inside the boilers. The AGRs in the UK operate with CO2. If there is a possibility of steam leaking into the gas, there could be a substantial amount of water condensing in the lower part of the boilers where the tube temperatures are lower.
There are very few experimental correlations for condensation in the presence of gases that can be applied with the high pressures and temperatures of the normal reactor operating conditions and therefore a computer modelling approach could help operators gain insight into this process and help identify possible critical scenario in the operation of the boilers.
Proposed R&D:
EDF Energy R&D UK Centre works closely with EDF R&D departments in France to share expertise and apply global technology to local problems. In particular, the use of Computational Fluid Dynamics (CFD) forms part of a strategic collaboration between the two companies. EDF R&D has developed the in-house software Code_Saturne/Neptune_CFD over the past 20 years and the UK Centre participates in the development of the code and its application to problem in the British reactor fleet.
The objective of the project will be to explore different CFD methodologies and develop new models to help with understanding of the steam condensation processes.
First phase of work will focus on the review of condensation modelling capabilities of available CFD codes against the wider literature. Some modelling approaches e.g. in Code_Saturne, use a homogeneous single-phase model with the heat and mass sink terms due to condensation estimated through correlations. Two-phase flow solvers such as Neptune_CFD include condensation models whose features and capabilities will be explored.
Once the literature survey has been carried out, application of the different methodologies to test cases relevant to the AGR boilers will help identify the most suitable approach. The selected models will need to be implemented into one of the codes developed by EDF, with any improvements necessary for improving the applicability range to the reactor conditions.