Abstract
Accurate modeling of thermal-hydraulic behavior is crucial during the design phase and for safety studies of nuclear reactor components. Precise models help avoid the need for overly conservative design margins, thereby reducing costs. Additionally, accurate transient behav-ior models are vital for understanding potential phenomena during non-design conditions. The Table Top facility at SCK CEN serves as a vital experimental platform, aiming to rep-licate the behavior of a single tube within the Primary Heat Exchanger (PHX) of the Multi-purpose hYbrid Research Reactor for High-tech. Applications (MYRRHA) reactor. How-ever, previous unqualified thermo-hydraulic models required unrealistic changes to param-eters such as the thermal mass and conductivity to match the transient behavior of the exper-iment.
This thesis investigates the thermal-hydraulic behavior of the Table Top facility using a 1D CFD model done in the software Flownex Simulation, which employs a Homogeneous Equation Model (HEM). Operating as a 2.5 kW water/steam open loop, the facility plays a crucial role in experimental validation, specifically assessing the thermal resistance of a dou-ble-walled bayonet tube under externally heated conditions. The primary objective of the thesis is to develop an improved model, evaluate its performance against experimental
measurements from the RUN#8.1 campaign and compare it to the previous unqualified model, with a focus on two-phase flow heat transfer and pressure drop.
To achieve this, the study implements a qualified TH system code nodalization approach and verifies its accuracy and reliability through transient and steady-state analyses. The re-sults show discrepancies in mass flow rate and subcooling estimates, despite Flownex align-ment with experimental pressure data. The model tends to overestimate mass flow rates and underestimate subcooling, highlighting limitations in the modeling approach. Attempts are made to match the pressure drop by adjustments to PHX components, which affect pressure buildup dynamics and thereby influence eventual mass flow rates and two-phase flow re-gimes. The latter thereby affects the heat transfer and degree of subcooling. These findings emphasize the ongoing need for refinement, model qualification, and validation to enhance nuclear reactor simulation accuracy.
This thesis investigates the thermal-hydraulic behavior of the Table Top facility using a 1D CFD model done in the software Flownex Simulation, which employs a Homogeneous Equation Model (HEM). Operating as a 2.5 kW water/steam open loop, the facility plays a crucial role in experimental validation, specifically assessing the thermal resistance of a dou-ble-walled bayonet tube under externally heated conditions. The primary objective of the thesis is to develop an improved model, evaluate its performance against experimental
measurements from the RUN#8.1 campaign and compare it to the previous unqualified model, with a focus on two-phase flow heat transfer and pressure drop.
To achieve this, the study implements a qualified TH system code nodalization approach and verifies its accuracy and reliability through transient and steady-state analyses. The re-sults show discrepancies in mass flow rate and subcooling estimates, despite Flownex align-ment with experimental pressure data. The model tends to overestimate mass flow rates and underestimate subcooling, highlighting limitations in the modeling approach. Attempts are made to match the pressure drop by adjustments to PHX components, which affect pressure buildup dynamics and thereby influence eventual mass flow rates and two-phase flow re-gimes. The latter thereby affects the heat transfer and degree of subcooling. These findings emphasize the ongoing need for refinement, model qualification, and validation to enhance nuclear reactor simulation accuracy.
| Original language | English |
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| Qualification | Master of Science |
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| Date of Award | 29 Aug 2024 |
| State | Published - 29 Aug 2024 |