Analysis of the table top experiment run#8.1 by means of a systems thermal-hydraulic code : master’s thesis

Bakhit, Afra (author), Hyvärinen, Juhani (mentor), Tiselj, Iztok (comentor), Potgieter, Marinus (comentor), Vihavainen, Juhani (comentor)

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 behavior 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 replicate the behavior of a single tube within the Primary Heat Exchanger (PHX) of the Multipurpose hYbrid Research Reactor for High-tech. Applications (MYRRHA) reactor. However, previous unqualified thermo-hydraulic models required unrealistic changes to parameters such as the thermal mass and conductivity to match the transient behavior of the experiment. 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 double-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 results show discrepancies in mass flow rate and subcooling estimates, despite Flownex alignment 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 regimes. 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.

• Language: English
• Keywords: nuclear engineering, two-phase flow, heat exchanger, MYRRHA reactor, Flownex
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FMF - Faculty of Mathematics and Physics
• Place of publishing: Lappeenranta
• Publisher: A. Bakhit
• Year: 2024
• Number of pages: 1 spletni vir (1 datoteka PDF ([100] str.))
• PID: 20.500.12556/RUL-160517
• UDC: 621.039.5
• COBISS.SI-ID: 204050947
• Publication date in RUL: 29.08.2024

Secondary language

• Language: Slovenian
• Title: Analiza »Table Top RUN#8.1« eksperimenta s sistemskim termohidravličnim programom
• Keywords: jedrska tehnika, dvofazni tok, toplotni izmenjevalnik, jedrski reaktor MYRRHA, program Flownex