Analysis of design basis conditions and design extension conditions is a major task in safety analysis of nuclear reactors. Loss of coolant accidents (LOCAs) are postulated initiating events which can lead to fuel pin failures, and in extreme cases to the distortion of fuel bundle geometry. This can cause change in flow field and shift in the efficiency of cooling conditions within the reactor core. In the Fuel and Reactor Materials Laboratory of ELKH Centre for Energy Research there are experiments underway in which inactive fuel pin bundles are brought to LOCA conditions and real fuel pin cladding tubes are suffering damages similar to accidental ones. Later three dimensional scanning will be applied to the distorted fuel pin bundles, which will provide with 3D numerical data on that irregular fuel geometry. This geometrical information could be used for further experimental and numerical thermal-hydraulics studies.
Particle Image Velocimetry (PIV) is a state-of-the-art non-intrusive optical flow measurement method based on the recording images of the movement of flow-following particles added to the liquid in the investigated flow domain. PIV is in use at BME Institute of Nuclear Techniques (NTI) since 2007, and has been applied for such investigations as coolant mixing in Allegro fuel bundles, heat transfer of the fuel rod of the training Reactor or thermal-hydraulics characteristics of the MSFR molten salt reactor concept core.
The data provided with PIV measurements will support the deeper understanding of flow behavior in the investigated geometries, and serves as basis for computer code validation. The verification and validation of three dimensional Computational Fluid Dynamics (CFD) codes is especially relevant. The major objective of this PhD research is to deliver new CFD-grade experimental data for distorted fuel bundle geometries and which would be applicable for the validation of CFD codes and other relevant models. Further task in the PhD research is to enhance the evaluation methods and tools used for PIV measurement data processing.
The PhD candidate would perform the following tasks:
- Study the latest findings of the international literature on Particle Image Velocimetry and its application in nuclear thermal-hydraulics, especially in investigation of reactor core thermal-hydraulics.
- Based on 3D data reproduce typical distorted fuel bundle geometries for PIV measurements.
- Design experimental models that will be used for extensive series of PIV measurements in distorted hexagonal fuel rod bundle geometries representing fuel pin bundles damaged within LOCA conditions.
- Perform measurements on the experimental model, analyze the measurement results and discuss the flow characteristics.
- Compare the PIV results with other highly sophisticated measurements like LDA (if available).
- Investigate the possibilities of two phase flow PIV measurements in the studied geometries.
- Develop more advanced evaluation methods and image processing tools to be used for PIV measurement data processing.
- Draw conclusions on the cooling conditions in fuel bundle geometries damaged in LOCA events.
- Documentation of measurement results on a level which is applicable for validation of numerical models and codes.
- Adequate knowledge of nuclear reactor thermal hydraulics and Computational Fluid Dynamics or deep knowledge in precision mechanics and optics
- Capabilities and good manual skill in design, construction and operation of experimental setups and test rigs
- Basic knowledge of measurement techniques applied in thermal-hydraulics
- Good knowledge and experience in lasers, precision mechanics and optics
- Affinity for using computational modelling tools, applying experimental methods
- Good level of English
- Diligence, precision, commitment