Experimental study on the measurement of effective themal conductivity for VHTR fuel block geometry

Abstract

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.

Effective thermal conductivity models which can be used to analyze the heat transfer phenomena of a prismatic fuel block were evaluated by the experiments. In the accident condition of VHTR when forced convection is lost, the heat flows in radial direction through the hexagonal fuel blocks that contain the large number of coolant holes and fuel compacts. Due to the complex geometry of fuel block and radiation heat transfer, the detail computation of heat transfer on the fuel block needs excessive computation resources. Therefore, the detail computation isn't appropriate for the lumped parameter code and a system code such as GAMMA+ adopts effective thermal conductivity model. Despite the complexity in heat transfer modes, the accurate analysis on the heat transfer in fuel block is necessary since it is directly relevant to the integrity of nuclear fuel embedded in fuel block. To satisfy the accurate analysis of complex heat transfer modes with limited computing sources, the credible effective thermal conductivity (ETC) models in which the effects of all of heat transfer modes are lumped is necessary. In this study, various ETC models were evaluated with the experiment result. Experiments for measuring the ETC values of the VHTR fuel block geometry were conducted with IG-11 graphite block. And four probable models compared to the experiment result showed good agreement with them, and thus they could be a candidate ETC model for VHTR fuel block.