Design of an experimental loop for post-LOCA heat transfer regimes in a Gas-cooled Fast Reactor

Abstract

The goal of this thesis is to design an experimental thermal-hydraulic loop capable of generating accurate, reliable data in various convection heat transfer regimes for use in the formulation of a comprehensive convection heat transfer correlation. The initial focus of the design is to ensure that the loop will be able to generate the convection flow regimes found in post Loss of Coolant Accident (LOCA) operation of a Gas-cooled Fast Reactor (GFR). As a result a scaling analysis of the proposed test facility was undertaken to demonstrate that the proposed loop would be able to operate in these aforementioned regimes. Having verified that the experimental loop could operate in the regimes of interest the next stage in the project was construction of the loop. Following construction of the loop and necessary instrumentation, an uncertainty analysis of the facility was conducted with the goal of determining the uncertainty associated with the calculation of heat transfer coefficients from the experimental data. The initial results were discouraging as the uncertainty calculated was large, ranging from -10-60%. After performing a heat transfer coefficient uncertainty analysis, we observed that the bulk of the uncertainty was clue to heat loss from the fluid to the environment.

(cont.) Therefore, guard heaters were implemented into the loop design, to match the inner surface temperature of the insulation to the wall temperature of the test section, which allows minimization of heat loss to about zero. This resulted in the considerable reduction in heat transfer coefficient uncertainty to -8-15%.